1

Review of Literature on Effects of Slurry Use on Crop production

FINAL REPORT

Submitted by: Jit B. Gurung, Ph.D. Freelance Consultant

Post Box #2314, Kathmandu, Nepal Telephone: 00977-1-520597 Fax/Tel.: 00977-1-535963

To:

The Biogas Support Program Post Box 1966 Kathmandu, Nepal

June 1997

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TABLE OF CONTENTS

Page Table of contents I-IV Abbreviations V Preface VI Summary, conclusions and recommendations Vll-X Chapter 1: Objectives, rationales and methodology 1 -4

1.1. Introduction 1 1.2. Rationales of the study I -3 1.3. Objectives 3

1.3.1. Overall objective 3 1.3.2. Specific objectives 3

1.4. Scope 3 1.5. Methodology 3

1.5.1. Interview 3 1.5.2. Literature search 3-4

Chapter 2: Nutrient constitution of bioslurry 5-18

2.1. Organic matter and plant nutrients 5 2.2. Nutrient supply 5-6 2.3. Improvements in the soil chemical,

physical, and biological properties 6 2.4. The nitrogen cycle vis-a-vis organic

matter 6 2.5. Nutrient composition of biogas

slurry in different forms 7-8 2.5.1. Overview of past research in

anaerobic digestion 7 2.5.2. Early research on the nutrient

value of slurry 7-8 2.5.3. Contemporary research on

nutrient value of slurry 8-1 5 2.5.4. Nitrification studies and the issues of

nitrogen conservation in digested slurry 15-17 2.5.5. Other nutrients 17 2.5.6. Bioslurry and the physical, biological

qualities of soil 18 Chapter 3: Effects of biogas slurry on crop production 19-51

3.1. Background to the study of manurial value of biogas slurry 19

3.2. Contemporary research 19-51 3.2.1. Slurry research in Nepal 21 -24 3.2.2. Slurry research in other countries 24-43

3.2.2.1. Slurry utilization in seed treatment insect/pest control and foliar dressing 44-51

Chapter 4: Sanitation and public health aspects of slurry utilization in crop production 52-67

4.1. Preliminaries 52 4.2. Excreta born organisms and diseases 52-54 4.3. Research in pathogen/parasite elimination

and survivability 54-65 4.4. Sanitary regulation 65 4.5. Biogas slurry utilization and health and sanitary

improvements 65

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4.6. Biogas slurry utilization and health and sanitation in Nepal 66-67

Chapter 5: Slurry treatment 68-77 5.1. Biodigested fresh liquid slurry 68 5.2. Treatment of slurry 69-76

5.2.1. Liquid biogas slurry storage 69 • Application of liquid slurry 69-70

5.2.2. Dehydration 70 5.2.3. Filtration 70-71 5.3.2. Centrifugation 71 5.2.2. Composting of biogas slurry 72-76

5.2.5.1. Composting methods 72-76 5.2.5.1. a. Open window method 73-76 5.2.5.2. b. General composting 74 5.2.5.3. c. Pit composting 74-76

5.2.5.2. Pathogen/parasite reduction by composting 76-77 Bibliography 78-87 General references 88-93 Prologue 94-95 List of tables: Table 1 : Effects of slurry on agricultural production 2 Table 2 : Advantage of slurry over dung 2 Table 3 : Total solid content (dry matter) of fermentation materials commonly found in rural areas (approximation) 9 Table 4 : Carbon: nitrogen ratio of feedstock commonly adopted (approximation 9 Table 5 : NPK values of fresh cow dung slurry 10 Table 6 : Composition of spent slurry from nightsoil biogas plant 10 Table 7 : NPK content of sun -dried bioslurry 10 Table 8 NPK content of bioslurry and FYM 10 Table 9 : Quality and composition of human faeces and urine 11 Table 10 : Characteristics of nightsoil 11 Table 11 : Manurial value of slurry and other characteristics of human excreta fed to biogas digesters 11 Table 12 : Average composition of nightsoil and urine 11 Table 13 : Composition of spent slurry from nightsoil biogas plant 12 Table 14 : Effect of digester manure on physical and chemical properties of Soil 12 Table 15 : Comparison of loss of nitrogen between digester manure and farmyard manure 12 Table 16 : Approximate range of nutrient contents of digester manure 12 Table 1 7 : Average constitution of fresh dung, dung slurry, digested slurry 12 Table 18a : Constitutions of different forms of organic manure 13 Table 18b : Average constitutions of fresh chicken dropping, and fresh cattle buffalo, and pig dung from samples collected from different parts of Nepal 14 Table 18c : Average constitutions of fresh slurry from biogas plants with and without toilet attachment 14 Table 18d: Nitrification of digested slurry 15 Table 19a: Nitrification of digested slurry 15 Table 19b: Mean yield/pot of grain, straw of wheat and marua (Eleusine coracona) and Total Dry Matter of sannhemp 20 Table 20 : Plot fertilizer experiment, Maya Farms, Philippines 20

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Table 21 : Mean yield of rice (grain) and berseem (dry fodder) 21 Table 22 : Effect of biogas slurry (dry and fresh on wheat yield) 21 Table 23 : Comparison of the effects of biogas slurry and other manures on wheat yield 22 Table 24 : Effects of biogas slurry on paddy, tomato, cauliflower, French bean, wheat, and maize 22 Table 25 : Effect of biogas slurry on wheat yield under irrigated and rainfed conditions 23 Table 26 : Effect of azotobactor inoculation of biogas slurry and other compost manures on wheat yield (kg/ha) 23-24 Table 27 : Comparison of the effect of effluent and FYM on the yield of rice, maize, wheat, and cotton 25 Table 28 : Comparative yields of cucumber for varying quantities of effluent vis-a- vis chemical fertilizer 25 Table 29 : Comparative effects of different doses of slurry and slurry-chemical fertilizer combinations on tomato production 25 Table 30 : Effect of biogas slurry with and without mineral fertilizer on mungbean yield 26 Table 31 : Effect of biogas slurry with and without mineral fertilizer on sunflower yield 26 Table 32 : Average yield of vegetables with mineral fertilizer and effluent application 27 Table 33 : Changes in soil NPK levels after slurry application 27 Table 34 : Effects of various fertilizer combinations on the yields of cabbage, mustard, and potato 28 Table 35 : Effect of slurry on the yield of different crops in India (Khariff, 1988) 28 Table 36 : Effect of biogas slurry on crop yield in the Indian States (Rabi, 1988-89) 29 Table 37 : Effect of different types of manures and fertillisers on the growth of tomatoes 29 Table 38 : Effect of different types of manures and fertillisers on growth of chillies 30 Table 39 : Summary of results of slurry demonstrations conducted by concerned state departments/agencies in India (1984-85 to 1990-91) 30-31 Table 40 : Summary of results of demonstrations on the effect of biogas slurry on crop production (GSFC, India, 1989-90) 31 Table 41 : Summary of the evaluation of manurial value of biodigested slurry

for various cereals and other crops in different agro-climatic zones in India 32-33

Table 42 : Effect of biogas slurry on rice grain and straw yield in South India 34 Table 43 : Effect of biogas slurry in crop yield in China 35 Table 44 : Comparative effects of digester effluent and open air pool manure on crop yield 36 Table 45 : Effect of digester sludge on crop yield in China 36 Table 46 : Effect of digester effluent + (NH4)HCO3 on the yield of rice and maize in China 36 Table 47 : Details of the study pertaining to comparative

effect of different fertilizers on pea, okra, soybean, and maize in Himalchal Pradesh, India 37

Table 48 : Effect of biogas slurry on pod/cob size, plant height and yield of pea, okra, soybean and maize 38 Table 49 : Comparative effects of chemical fertilizer and biogas slurry + chemical fertilizer on various crops,

North Karnataka. India 39

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Table 50 : Direct and residual effect of bio-digested slurry on rice and blackgram 40 Table 51 : Effect of plain and enriched slurry on rice-blackgram cropping system 40 Table 52 : Effect of biogas slurry and chemical fertilizer on different vegetable crops 41 Table 53 : Effect of biogas manure on crop yield in Egypt 43 Table 54 : Yield of string bean treated with different organic manures and chemical fertilizers 43 Table 55 : Effect of seed coating biogas slurry on rice yield 45 Table 56 : Seed coating In sorghum Tamil Nadu, India 45 Table 57 : Efficiency comparison of seed coating with digester slurry and fresh water (rice) 46 Table 58 : Comparison of results of different seed soaking methods (wheat) 47 Table 59 : Excreta-borne organisms and diseases 53 Table 60 : Percent reduction of helminth ova in laboratory night soil digester 55 Table 61a : Survival time of pathogens In some excreta disposal system 56-57 Table 62b : Temperature, residence time and die-off rate of parasites and pathogens 57 Table 62 : Comparison of pathogen survival in unheated digestion and composting 57-58 Table 63 : Organisms isolated from farm manures and non-digested nightsoil 58-59 Table 64 : Settling time of some of the common pathogenic ova 62 Table 65 : Survival periods of schistosome ova 62 Table 66 : Fatality rates of hookworm ova 63 Table 67 : Fatality rates of ascaris ova (summer and autumn 63 Table 68 : Pathogen survivability under different temperatures 68 Table 69 : Relation between feedstock concentration and the survival time of schistosome ova 64 Table 70 : Comparison of FYM and biogas slurry pit composting 74 Table 71 : Constraints faced by farmers in slurry compost making 75 Table 72 : Quality of compost against FYM 75 Table 73 : Farmers, perceptions on the quality of slurry compost 75 Table 74 : General composition of slurry compost based on cattle dung based slurry 76 Table 75 : Effect of biogas phospo-humate on major crops 76 Table 76 : Pathogen elimination and survivability in unheated anaerobic digestion and composting 77

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Abbreviations

APROSC Agricultural Projects Services Centre APRBRTC Asian-Pacific Regional Biogas Research-Training Center, Chendu, China AFPRO Action for Food Production ATC Agricultural Technology Center AAU Assam Agricultural University BSP Biogas Support Programme CIE Central Institute of Agricultural Engineering (India) C:N Carbon Nitrogen Ratio C:P Carbon Phosphorous Ratio CMS Consolidated Management Services CD Critical Difference DevPart Development Partners-Nepal (P) Ltd. DOST Department of Science and Technology (India) ENFO Environmental Sanitation Information Center (Bangkok, Thailand) FYM Farmyard Manure FORRAD Foundation for Rural Recovery and Development g Gram GSFCI Gujrat State Fertilizer Co-operative (India) GGC Gobar Gas Company HRT Hydraulic Retention Time HPAU Himalchal Pradesh Agricultural University (India) ha Hectare ICIMOD International Center for Integrated Mountain Development IARI Indian Agricultural Research Institute IFFCO India Farmers' Fertilizer Co-operative Irs Indian Rupees kg Kilogram LARC Lumle Agricultural Research Center Ib Pound MGT Mean Germination Time MRL Mean Root Length MSL Mean Shoot Length MNES Ministry of Non-Conventional Energy Sources (India) NPK Nitrogen, Phosphorous, Potassium NARC National Agricultural Research Centre O.M. Organic Matter PARC Pakhribas Agricultural Center PAU Punjab Agricultural University (India) RAJAU Rajasthan Agricultural University (India) SEP Slurry Extension Programme SNV Netherlands Development Organization SSP Single Superphosphate SDS Sun-dried slurry TERI Tata Energy Research Institute (New Delhi, India} TS Total Solids TNAU Tamil Nadu Agricultural University (India) t Ton UAS University of Agricultural Sciences (Karnataka, India) W/W Weight by Weight WECS Water and Energy Commission Secretariat

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PREFACE

This study is a review of literature pertaining to the use of slurry, a by-product {some prefer to call it 'primary product' in view of its perceived importance as a high value fertilizer) of biogas plant, in crop production. Virtually no research work is currently under way on this important aspect of biogas technology in Nepal. Few preliminary works were initiated during the late 1970s after the incorporation of biogas promotion programme in the Agriculture Year (1974-75). However these works stopped abruptly after few trials in Khumaltar. After a two decade long hiatus, the interest on the issue has been aroused once again by SNV Nepal's Biogas Support Programme. It was understood right in the beginning of this study that materials on this aspect are scanty in Nepal. Nonetheless, some efforts were made to search materials in the major institutions and documentation/information centres both in Kathmandu and in other areas of Nepal. No substantive review materials were available. Since India is an important 'biogas country', and since both the biophysical and socio-cultural environments, at least at the macro level, are similar to that of Nepal, a trip to Delhi was planned and it was fruitful from the point of view of the task at hand.

While in Delhi Dr. K.N Khandelwal, adviser to the Ministry of Non-Conventional Energy Sources and head of its Rural Energy division, gave me important advises about where to visit and whom to contact in Delhi; Mr Anil Dhussa of the same ministry also extended his cooperation. The discussion with Mr. ]. B. Singh of FORRAD (Foundation for Rural Recovery and Development) was very useful. Together these individuals can be considered as the doyens of Indian slurry research activities. I am grateful to them all. The people at the Tata Energy Research Institute library were very cooperative. 1 must thank them for this and their excellent library. Special appreciation is also extended to Mr. Balbir Singh of the TERI library for responding to my queries and for being ready to help me whenever I needed him during my work in that library. The cooperation extended by all other individuals in Delhi is also gratefully acknowledged.

In Nepal, the guidance provided by Mr. Wim J. van Nes, Programme Manager of the SNV/ Biogas Support Programme is gratefully acknowledged. The materials provided by him were immensely important for understanding the state of biogas technology in Nepal. Mr. Bhimsen Gurung, the Slurry Extension Specialist with the BSP, was always at hand to share whatever relevant material he could garner during the course of his work. I must thank him for that.

In addition the cooperation extended by the following individuals is acknowledged:

Mrs. Renu Sherpa, BSP, ]hamsikhel, Lalitpur Mr. L.K. Amatya, Lumle Agricultural Research Centre, Kaski, Pokhara. Mr. K.B. Kadayat, Lumle Agricultural Research Center Mr. Ananta Ghimire, Pakhribas Agricultural Research Center, Dhankuta. Mr. Gam Bahadur Gurung, Pakhribas Agricultural Research Center, Dhankuta. Mr. D.P Sherchan, Pakhribas Agricultural Research Center Mr. Dawa Sherpa, PARC Documentation Center. Ms. Indira Shrestha, PARC Documentation Center Mr. Khadka Jung Gurung, Consultant

Jit B. Gurung, Ph. D. May, 1997

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SUMMARY, CONCLUSIONS AND RECOMMENDATIONS

Summary & Conclusions

1. A review of the brief history of anaerobic digestion showed that the energy part (methane generation) received more attention since the early decades of this century when research into biodigestion had gradually begun to take shape. Fertilizer aspect received occasional attention a couple of decades latter. Emphasis on the. energy aspect still dominates in many parts of the world today (with the notable exception of China). However, the environmentalism of the more recent years have somehow turned to be conducive for the appreciation of slurry manure as well as biogas technology as a whole.

2. This review was centred mainly on the effects of bioslurry utilization in crop production. Major research works, specially those carried out in India and Nepal, on the effects of different forms of slurry on crop yields were reviewed. Brief attentions to the works carried out in the area of nutrient research (especially, nitrogen), the health and sanitation aspects of bioslurry utilization in agriculture and slurry were also given.

3. There seems to have built a general consensus on the ability of biogas slurry to improve the physical and biological quality of soil besides providing both macro and micro-nutrients to crops. These improvements in physical and biological qualities include: improvement in soil structure, improvement in water holding capacity, cation exchange capacity, lesser soil erosion and provision of nutrients to soil micro-flora including nitrogen fixing and phosphorous solublizing organisms. In addition bioslurry is free of weed seeds. Anaerobic digestion kills more seeds than any manure processing system (It is not the methane that kilts the seeds; it just inhibits germination. Most importantly, it is the free ammonia that kills the seeds). On the other hand, FYM, if left to itself, (open pool manure) looses nutrients, most importantly, nitrogen, and thus possess relatively lower manurial value than biogas slurry. Fresh dung also contains viable weed seeds that compete with the crops and requires farmers to put extra labours for weeding. From the points of view of nutrient recycling, sustained agricultural production, and forest and environmental preservation, the use of forest wood, agricultural and animal wastes as fuel (which constituted 72%, 16% and 9% of the total energy consumption of Nepal in 1992/93), is not a desirable practice. Biogas technology provides alternatives to both fuel and fertilizer.

4. The review reveals that analysing the composition, and thus determining manurial values, of fresh slurry, sun dried slurry, and slurry compost is an exceedingly complicated endeavor, effected, as it is, by numerous varieties of circumstances ranging from sampling procedures to animal species to feedstocks fed both to the animals and biogas plants. The literature reveals an almost idiosyncratic constitutions of these different forms of biogas slurry. Furthermore, research reports often do not clearly elaborate the research protocols and procedures about how different figures are arrived at. Because of these, a comprehensive picture of the composition of different forms of biogas slurry is lacking. Even with these limitations, following extension educational messages could be give to the farmers:

• Storage, handling, treatment and application procedures are very important for nutrient conservation and increased crop yield. In no way manures in all these forms should be recklessly exposed to the vagaries of nature.

• Biogas digester does not ' use up' plant nutrients • As there may not be congruence between the time of availability of fresh slurry and the time

of field application, liquid slurry should be properly stored or composted. If liquid application is not practical, composting is the best alternative. Here comes the importance of having 2-3 compost pits near the biogas plant.

• No form of biogas slurry can be profitably left spread on the field. Fields should be ploughed immediately, or if the manure is used as top-dresser, should be covered by soil immediately, Nutrients.

• Biogas plants with toilet attachments can significantly improve health and sanitation of community

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and community members. • Use of fuel-wood, agricultural and animal wastes for fuel will gradually deplete soil nutrients and

thus contributing to the emergence of unsustainable agricultural systems. Although FYM can be directly returned to the soil or composted to complete the nutrient cycle, its utilization in biogas generation has two pronged advantages i.e. energy and better manure (if handled and treated properly).

In addition, the review reveals a number of findings on the comparative effects of slurry and other organic manures and chemical fertilizers on yields of a number of crops. These may be of potential benefits to farmers if they are suitably translated to the local situations.

5. Some of the major findings1 pertaining to the comparative effects of slurry and other organic manures and chemical fertilizers on crop yield are summarized below for their potential use by Slurry Extension Officers. However these findings are presented to serve 'sensitizing' purposes only, for both the manurial value of slurry and their potential applications for different crops are dictated by numerous factors including animal and biogas plant feed stocks, treatment and handling procedures, agro-climates and geophysical environments.

Effects on crop yields • A combination of biogas slurry @ 12.5 t/ha and 100% NPK had pronounced effect on rice

yield.

• Seed coating with a combination of digested slurry at 50% (W/W) of seed + inorganic nutrient at 2% + biofertilizer at 2% enhanced growth and yield attributes of rice.

• Application of biogas slurry @ 10 t/ha to the first rice crop favourably influenced the following blackgram crop. Slurry increased rhizobium nodules and increased the blackgram yield by around

78%.

• Gypsum enriched slurry when applied in combination with 75% recommended NPK gave maximum grain yield in rice-blackgram cropping system. Estimations showed that 25 kg N/ha was saved.

• Biogas slurry applications on wheat, sunflower, sunflower, hybrid cotton, and groundnut gave an average yield increase of 24% over the control.

• Application of biogas slurry @ of 10 t/ha in potato, tomato, brinjal, groundnut, jowar, maize, and okra gave better yields than FYM. (Reports, however, are usually not clear about the physical form of the slurry used)

• Seed coating with 50% (W/W of seed), organic nutrient at 2% and biofertilizer at 2% also increased the growth and yield of soybean, blackgram, greengram, and jowar.

• Yield increases due to bioslurry application, have also reported for many other crops including peas, mustard, watermelon, cabbage, banana, chillies, bajra, turmeric, sugarcane, deccan hemp, mulberry, tobacco, castor, and onion.

• A combination of liquid biogas slurry and chemical fertilizer enhanced carbon nitrogen transformation with substantive effect on crop yield. The yields in many instances are reported to be higher than that given by the combination of ordinary FYM and chemical fertilizer. In China although the average yield increment reported is not as high as in India (somewhere around 10 to 18 percent), experiments in bioslurry-chemical fertilizer utilization showed yield increment by as

1 It should, however, be considered that these results are based predominantly on slurry research done in India and slurries used were mostly derived from cattle and buffaloes. Some of the findings on slurries derived from human excreta are given in the main text.

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high as. 37.8% in maize as compared to 16.8% and 9.4% respectively for effluent and chemical fertilizer alone. A comparatively lower, nonetheless increased yield, has also been recorded for rice with such combinations.

• Vegetable crops produced with bioslurry have better quality as compared to those produced with chemical fertilizer. Studies have not pinpointed the differences between bioslurry and FYM in this regard.

6. Nitrification research carried out so far indicate that properly handled bioslurry as a manure is superior to ordinary farmyard manure. Mineralization rate of nitrogen is higher in biogas slurry than in ordinary, undigested manure, which alone provides a sound empirical basis for slurry extension programmes. This is the majority view and is technically right However, dissenting views begin to arrive in the picture (elaborated in detail in the main text) when discussion of the preservation of nutrients from the digester to the field takes place. This quote from Van Brakel is pertinent here: 'During the early 1950s, when interest in anaerobic digestion in Germany was greatest, it was argued that the loss of cellulose and nitrogen during conventional manure processing was about equal to the amount of these chemicals sold in Germany in 1950. With nitrogen losses during conventional manure processing of 18% or higher, anaerobic processing of manure would seem very attractive, because in principle, nitrogen losses during this process can be zero. Moreover, it may be expected that manure processed anaerobically contains a large amount of nitrogen that is readily assimilated by plants. Various laboratory experiments support the contention that these advantages hold. However, there is a difference between what is possible in principle and how things turn out in practice' (Van Brakel, 1980:104). Thus, the way slurry is handled after it comes out of the digester for Van Brakel, is a matter of utmost importance. His conclusion is that superior manurial value of slurry cannot be taken for granted just because it is anaerobically digested; attention must be given to nutrient conservation from the moment it comes out of the digester to the moment it is applied in the field. However critics of slurry promotion like Van Brakel and Tam et al.(1983) are pessimistic about preventing nitrogen fosses from the small scale operations in rural areas and see no advantages in slurry promotion. This is exactly where the role of education, in the form of slurry extension, is important, for slurry extension agents can closely work with the farmers to jointly identify the major causes of nutrient losses and advise and facilitate the mitigation of these causes.

7. In the field condition, the effects of fresh slurry (cattle and buffalo) vis-a-vis- sun-dried slurry, was at times, ambiguous. Toxicity, mainly due to hydrogen sulphide and excess ammonia accumulation, is often presumed to be the reasons in many cases.

8. Significant number pathogens/parasitic species are eliminated by the anaerobic digestion process. However, both temperature and HRT is an unsettled issue among the researches. It has been accepted by all the researchers that the level of temperature is the determinant of not only the elimination rate of pathogens, it is also an important determinant of which group of methanogenic bacteria will function in the digester. Reports from various experiments have shown that pathogens are killed faster and the slurry well digested in the thermophilic range of temperature(48-60°C). But the production of this range1 of temperature requires external source of energy. Mesophilic methanogenic bacterial digestion (3OJ4O°C) is considered ideal for household biogas plants, but again maintenance of a common temperature range is important--a temperature fluctuation by a mere 2-3° C affects the methane forming bacteria. The idea of fixing appropriate temperature for the elimination of different parasites and parasitic ova has not reached consensus in the literature. The design aspect also enters into the debates and controversies. Nonetheless, it is accepted that the remaining number of pathogens and parasites/parasitic ova can be substantially reduced if bioslurry is used for composting.

9. On the whole, fresh slurry is better in terms of manurial value than ordinary farmyard manure, ordinary compost and other forms of slurry (sun-dried, slurry compost). Field results are however highly dictated by soil, moisture conditions, slurry storage modes, and application procedures. Nutrient conservation during liquid storage, composting and drying is very important to utilize the true potential of fresh slurry. Transportation of liquid slurry, however, is a major constraint in the South Asian context.

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10. Slurry derived from human excreta is far more superior in terms of manurial value, but wide scale

adoption of this technology has not taken place in Nepal and India. In comparison, China is doing far better in this aspect. Sociocultural traditions rather than scientific facts seemed to be dominant in this aspect. Slurry utilization in agriculture affected public health and sanitation in very positive and substantive ways { the case of China). Some indications of these are also available from India and Nepal. Utilization of human waste in biogas generation can be expected to significantly improve health, and sanitation in the rural areas of Nepal. In India, it has been reported that 80% of the human' diseases are due to the inability to manage human and animal waste properly. The annual loss in medical expenses and lost labour is estimated be around IRs 4.5 billion. The Nepali situation cannot differ much as far as pathogen contamination through unmanaged human and animal waste is concerned.

11. Slurry research in Nepal has ceased to exist since the late seventies. Information on slurry utilization suitable to Nepal's agro-ecology and climate is conspicuously lacking. Many research reports reviewed were uninterpretable. This indicates the relatively lower level of scientific sophistication and statistical rigorousness in slurry utilization research.

12. Finally, it seems that contemporary engagement with biogas technology with its two-pronged benefits- fuel and fertilizer-- is a reflection of the emerging concepts of sustainable development, ecology and environment. The ideas of ecological agriculture as reflected in the concepts of organic farming, natural farming, permaculture, and sustainable agriculture can be considerably enhanced with the adoption of biogas technology.

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Recommendations

1. Available literature indicates that chemical fertilizers suppress soil microbial activities while biogas slurry provides them energy. While it is difficult to find reports saying FYM be a suppressor of soil microbial activity (organic manures as a whole is generally considered more soil microbe friendly than chemical fertilizers), comparative studies of soil microbe friendliness of slurry and FYM is lacking. Such a study will benefit the Slurry Extension Program in devising its extension messages.

2. Studies have generally revealed that fresh slurry, properly stored slurry and composted slurry when combined with chemical fertilizer generally gives better crop yields than FYM + chemical fertilizer. Fresh slurry or properly stored slurry alone has also given better yields than FYM alone. If complete substitution of chemical fertilizer is not possible at high chemical fertilizer input areas at this stage, use of bio-slurry, at least in combination with chemical fertilizers, should be encouraged. In the mean time, as a comprehensive, comparative picture of composition of different forms of slurry and FYM is still lacking in the varied situations of Nepal, samples of these organic manures should be analysed to get the same and to backstop the Slurry Extension Programme with dependable technical information.

3. No ready extension messages are available regarding the relative appropriateness of organic materials for slurry composting. Scattered information on the composition of organic materials that are available in and around farms in Nepal should be collected and reviewed for their potential inclusion in slurry extension messages. Those plants and organic materials, the composition of which is not available in the literature, should be analysed.

4. Biogas slurry utilization should be seen (because it is so) as an integrative mechanism between energy, environment and agriculture. Even a partial substitution of chemical fertilizer (in the high chemical fertilizer input areas) by bioslurry will improve soil health, reduce pest infestation, and increase crop yield. In addition, the quality of some of the vegetables will be substantially better. These recommendations are made on the basis of studies done abroad with the assumption that at least no harm will be caused to the farmers due to the lack of data from Nepal

5. Experimental results vary substantially from place to place (soil, climate, form of bioslurry, feedstock fed to the plants, crop species and varieties, irrigation etc.) thus trials and demonstrations should be location specific.

6. Research in slurry utilization seems to have taken two modes. One mode is in line with the present thinking with the Farmer Participatory Action Research (Gurung, 1997) which is based on a epistemological premise that is different from the conventional, centralized institution based positivistic and empiricist orientation that demand high level of statistical regour. Proponents of the latter tend to believe that research should be for research's sake (excessive zeal for sophisticated designs). On the other hand, the proponents of the former mode believe that such a practice of science has lesser potential to help the farmers (Singh, 1977, personal communication). The proponents of what might be called the scientistic mode question the scientific validity of the conclusions reached by the former mode. Extreme position from either side is not going to be helpful. A middle of the road approach i.e. Farmer participation with due regards for validity, is a desirable strategy for slurry research programme in Nepal.

7. Research on slurry utilisation is usually a lesser priority area in many countries with Biogas Programmes. European and North American Commercial and chemical farming naturally put lesser degree of emphasis on slurry utilisation for crop production. During the mid-Eighties Demuynck (1984:147) reported that only Denmark, Switzerland and Germany among the European countries were studying the fertiliser value of digested slurry, in Nepal, institutional responsibility is not entrusted to any existing research facilities. The works initiated during the late seventies stopped abruptly. Current thinking on sustainable development in general, and sustainable agriculture in particular demands substantive and aggressive steps towards ecological agriculture. Research should take up from the currently existing knowledge to a systematic, farmer-based participatory

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slurry utilisation action research, taking into consideration agro-ecological and climatic specificities of Nepal.

8. Even the country's premier agricultural research institutions tike Pakhribas and Lumle have not yet done any work on slurry utilisation. Given their competence and facilities (the lab in Pakribas for example) they could be fruitfully integrated into the slurry participatory action research agenda.

9. Pathogens/parasitic ova survivability in digested slurry derived from human excreta is one issue, socio- cultural traditions inhibiting the productive utilization of this resource is an altogether different issue (China and India can be compared here). Research and extension efforts can be judged successful if some of the cultural constraints (taboos) associated with human faeces are effectively deconstructed and the nutrient rich product of the human biological system attained prestige as an important resource in the resource poor agricultural countries like Nepal.

10. Anaerobic digestion can significantly reduce pathogens and parasitic ova both in animal dung and human excreta; composting of slurry can kill the remaining pathogens/parasitic ova in the slurry. Anaerobic digestion can play an important role in the improvement of sanitation and public health. Vigorous educational campaigns are important here, and Slurry Extension Programme can play an important role in this.

11. The Slurry Extension Programme of the Biogas Support Programme intends to investigate into the possible involvement of the Department of Agriculture in slurry extension. This is an important idea the materialization of which should be pursued as soon as possible because this department has the most comprehensive country-wide extension network among the government agencies. The extension activities of the Department of Livestock Development and Animal Health could also be fruitfully coordinated with the Slurry Extension Programme. Such a mechanism would facilitate the use of existing livestock and agricultural commodity groups (farmers' groups) for dissemination of messages pertaining to slurry management and utilization in agriculture.

12. Nepal still has to initiate research activities in slurry utilization in agriculture. Nepal needs a series of participatory trials on the effects of slurry application on crop yields in its various agro-ecological and climatic zones. In the context of the BSP, it may carry out these activities in collaboration with competent individuals from non-governmental organizations, or alternatively, the Slurry Extension Programme of the BSP could train the SEOs for simple participatory trials and demonstrations. Such participatory trials, in the long, will be able to generate sufficient data to be incorporated in the slurry extension work. The current forms (Awareness Creation, Baseline Information, Farmers Visit, Result Evaluation,) used by BSP's SEP will mostly catch perceptions, opinions, and practices (as recalled) ; and over the years, the information captured by these forms will definitely provide important images of different aspects of slurry utilization. The information generated by farmer participatory trials and the information captured by the forms currently used by the SEP, when synthesized, can be expected to greatly enhance the SEP.

1

CHAPTER 1

OBJECTIVES, RATIONALES AND METHODOLOGY

1.1. Introduction

In Nepal, the traditional sources of energy include fuel-wood, agricultural residues and animal wastes. It has been estimated that these sources of energy met 91 percent of Nepal's total energy consumption for the year 1993 (WECS, 1994). Fuel wood accounted for around 68 % of the total energy consumption; the rest, around one fourth of the total consumption, was supplied by agricultural and animal wastes. In the situation of the dwindling forest area, which cannot meet the fuel-wood demand, and in the situation of the limited affordability of other sources of energy, felling of more trees arid burning of agricultural and animal wastes become the immediate ways to solve energy problems. The consequences for the environment and soil nutrient cycling is obvious. It has now been generally accepted that in many parts of the country, the fertility of soil is declining due to continuous cultivation without replenishing soil nutrient removal by crops with quality fertilizers in required quantity. Nepal does not produce chemical fertilizers and most farmers cannot afford to buy the imported fertilizer. Even for those who can afford to buy fertilizer, the undependability of availability has usually been a problem. Under these circumstances, putting emphasis on locally available low cost organic manure becomes an important option. In this context, the accelerated pace of biogas adoption in Nepal in the past few years offers possibilities for both fuel and locally produced organic fertilizer. In addition to energy generation, other major aspects of bio-gas technology is the bi-product known as bioslurry. Ideally, the efficient use of bioslurry as fertilizer should be an important dimension of the diffusion and adoption of this technology. With increasing number of bio-gas plants, slurry utilization for raising agricultural production and productivity has also begun to be a concern, since not using or misusing bioslurry is to deprive the organically poor soil from this potentially fertility enhancing resource. In addition, replacement of fuels from agricultural wastes, animal wastes and wood by fuel from biogas plants helps protect forests and supply soils with nutrients.

1.2. Rationales of the study

Many consider digested biogas slurry as important as biogas itself, it contains important plant nutrients and its use is consistent with the ideas inherent in sustainable agriculture and sustainable development, the ideas to which contemporary development thinkers and practitioners are putting much emphasis. Both the energy and the fertilizer provided by biogas plants form integral parts of an ecological cycle, and ecology is what sustainable development is importantly concerned with.

Nepal imports more than Rs 250 million of chemical fertilizer every year. It has been estimated that proper use of slurry produced by the potential number of biogas plants would save 54 percent in the purchase of N, 85 percent in P2O5 and a whopping 1,761 percent in K2O from the projected demand of these nutrients for the year 1996/97 (CMS, 1996:4-3). Despite the usual scientific claims that anaerobically digested slurry enhances soil fertility, and despite the estimations of potential replacements of mineral fertilizer, there does not exist too much reliable information on the influence of slurry on crop production.

A survey on GGC bio-gas plants (1990-91) (Gajurel et al., 1994:11-12) reported that 34 percent of the users were ambivalent about the 'fertilising value' of the bioslurry. East Consult (1994:22) in one of its studies reported that 52% of the respondents felt that "crop yields may decrease as all the nutrients in the dung were burnt off"; only 15 percent of the survey respondents felt that crop yield increased after the use of bioslurry. Another study conducted by Castro et al. (1994:21-22) reported that farmers in

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general insisted that the increase in crop yields because of the use of slurry has not been proved'. The farmers also reportedly felt that fertility effects of the slurry would not last as long as that of the raw dung. Another bio-gas survey for the year 1994-95 (East Consult, 1996 :24) reported that only 20 percent of bio-gas users among its respondents were using bioslurry. The shorter time periods between the construction of biogas plants and the conduction of some of these surveys should, however, be noted. DevPart (1996:36) reported that 93 percent of its respondents were reportedly using biogas slurry. Also DevPart's inquiry into the effects of slurry in agricultural production among biogas users (ibid.) reported that 19% of the user respondents experienced some increase in agricultural production. Some respondents (24%) even reportedly witnessed a decrease in production after the use of bioslurry. The replacement of inorganic fertilizer among these respondents was also reportedly not very encouraging as only 21% reported that they have lowered the quantity of inorganic fertilizer use after they stated using bioslurry. Table 1. below presents responses on the effect of bioslurry on agricultural production among respondents with and without toilet connection and among those without toilets.

Table 1: Perceptions on effects of slurry on agricultural production Effect Toilet not connected Toilet connected Toilet not

constructed * Row total

Increased significantly 1 5 1 7

Increased somewhat 7 8 4 19 Remained same 8 9 2 19 Decreased 8 12 4 24 Cannot say 11 18 2 31 Column total 35 52 13 100 Source: DevPart- Nepal, 1996:36 * Biogas adopters who do not have toilets

DevPart (ibid.) also made an attempt to assess the users' perception on the effectiveness of slurry over the farm-yard manure. Table 2 below presents data on such perceptions among respondents with and without toilet connection and among those respondents who did not have toilets constructed

Table 2: Advantage of slurry over dung General perception Toilet not

connected Toilet connected Toilet not

constructed* Row total

Better than dun? 1 I 14 4 29 Same as dung 6 10 3 19 Less fertile than dung 16 21 4 41 Cannot say 2 7 2 II Column total 35 52 13 100 Source: DevPart- Nepal, 1996: 36 * Biogas plant adopters who do not have toilets

Table 2 above shows that 41 % of the respondents think that bioslurry is less fertile than dung. In comparison only 29% thinks that bioslurry is better than dung.

The DevPart study also reports that the general perception of the biogas adopters is not effected by the toilet connection. In addition DevPart (1996:36) reports: 'In absence of reliable data on the actual increase or decrease in agricultural production because of the installation of biogas plants', it is difficult to quantify the benefits in monetary form. There is no reason to believe that production has increased significantly because of the installation of biogas plants. The major reason for this could be improper handling of the slurry and the lack of composting practice'. Furthermore, a big majority of the user respondents (86%) also reported that the quantity of

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available manure decreased significantly, affecting manure-supply on the fields.(ibid.). These reports indicate that bio-gas adopters in Nepal have neglected the proper use of bioslurry as fertiliser. Thus it seems that in the past little ' attention has been focused by the promoters as well as extension workers to promote scientific data in this subject' (CMS, 1996:4-5).

The rationales of this study are thus dear. There is a need to look into research works pertaining to the manurial values of digested slurry and their subsequent effects on crop production. This is important for biogas extension programmes because bio-gas owners ' seem to be misled about its effect on agricultural productivity' (Adhikary, 1996: 15). The SNV Biogas Support Programme (BSP), a premier biogas promotion programme in Nepal, recognizes this aspect of biogas promotion, in fact ' to increase agricultural production by promoting an optimal utilization of digested dung as organic fertilizer' (Cited in Britt, 1994:6) is one of the long term objectives of the BSP. After a review of studies conducted for the BSP Britt (ibid) has identified the following specific research areas to determine: 1) whether slurry is indeed a potent fertilizer; 2) how slurry can be used given the predominant mixed farming systems in the Terai and Middle Hills of Nepal; 3} different ways of composting to ease transport to fields; and, 4) the most efficient and economical use of the slurry as a fertilizer. Research on the use of composted slurry has also been incorporated in the proposal for BSP Phase III (SNV, 1996:38).

1.3. Objectives

1.3.1. Overall Objective

To review currently existing literature on the effect of digested slurry on crop production with a view to prepare a comprehensive volume for use by slurry extension workers and biogas policy makers.

1.3.2. Specific Objectives

• To review literature pertaining to the effect of different forms (fresh, sun dried, composted) of anaerobically digested slurry on crop production.

• To review heath and sanitation aspects of bioslurry utilization in crop production. • To review literature on slurry treatment for use in crop production.

4. Scope

This review was confined to the effects of digested slurry on crop production in the existing agroeco logical conditions and the prevailing socio-cultural milieus in Nepal and adjacent areas with similar agroeco logical and socio-cultural environments. It did not deal with its effects on livestock production, fisheries, poultry production, and piggery.

5. Methodology 5.2.1. Interviews Persons involved in slurry extension and research in Nepal and India were interviewed. 5.2.2. Literature search Literature search was done by visiting following institutions: • APPROSC library • Department of Agriculture library

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• Division of Soil Science and Agricultural Chemistry, NARC, Khumaltar • Department of Livestock Development

Library of the National Agriculture Research Council • Library of the Institute of Agriculture and Animal Sciences, Rampur • Lumle Agricultural Research Center and its library • Pakhribas Agricultural Research Centre land its library • BSP • ICIMOD library and documentation center • Library of Tata Energy Research Institute, New Delhi

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CHAPTER 2

NUTRIENT CONSTITUTION OF BIOSLURRY

2.1. Organic matter and plant nutrients

As the present context is the availability of plant nutrients from organic sources it is useful to briefly discuss about the organic matter and how plants derive nutrients from it.

Though it is present in small quantities, organic matter has a major influence on the physical and chemical properties of soils. As it breaks down, it releases nutrients in a form which can be taken up by plants and crops. Organic matter also helps bind soil particles together, and improves its waterholding capacity. And more importantly, it is responsible for the physical and ecological stability of the soil.

When plant materials or animal manure is added to the soil, it does not stay in its original form for long. It is immediately attacked by a host of different soil organisms and undergoes a complex series of biochemical steps leading ultimately to its complete breakdown. The bulk of the material undergoes an oxidation or burning' process in which the carbon and hydrogen which make up about half of the dry weight of organic matter combine with oxygen to produce carbon dioxide and water. Energy is released in the process, and this is what is used by bacteria and other soil microorganisms for their survival and growth.

As the basic structure of the plant material is broken down (the breakdown may start from a series of intermediary steps like the digestive system of living creatures and anaerobic fermentation process or it may start from the soil itself if these materials are returned to the soil as such), nutrients such as nitrogen, phosphorous, potash, sulphur, etc., are released from their original organic form. Part of these may become soluble, and therefore be immediately available to growing plants. Most are, however, taken up by microorganisms and stored in their tissues as they grow and multiply. These are only released when original plant matter has been used up and the organisms themselves start to die off and decompose. A variety of complex organic products accumulate in the soil as the process of decomposition continues. These include lignins and other materials that are resistant to decomposition as well as polymers derived from microbial products. This more or less stable fraction is called humus. It is usually dark in colour and persists in soil for many years, degrading very slowly but being replenished each year by the new additions of organic materials.

The breakdown of organic matter depends on a variety of soil and site conditions. Nutrient and pH status, moisture content and temperature, and the availability of oxygen for soil microorganisms affect the rate of breakdown of organic materials.

2.2. Nutrient supply

In traditional agricultural systems where very little or no chemical fertilisers are applied, breakdown of organic materials supplies the dominant portion of nitrogen and sulphur needed by plants and as much as half of the phosphorous (Bernard, 1985). Organic matter considerably enhances, the cation exchange capacity of the soil - that is, its ability to bind positively charged ions such as magnesium, calcium, potassium and ammonium. Without this binding effect, these nutrients would be rapidly leached away when it rained. Cation exchange ability of the organic matter is particularly important in acid soils, and those with low clay content since such soils have low binding ability. Organic matter also forms complexes with micro nutrients such as iron, manganese, boron and copper and through binding prevent them from being lost through leaching. Phosphorous availability is increased with the presence of organic matter. This occurs when organic matter forms complexes

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with amorphous ion in the soil thus preventing them from binding and immobilizing phosphate ions. The pH range of the soil is an important condition for many chemical reactions and microbial activities in soil. Organic matter helps buffer the soil pH by keeping it towards the neutral range. This increases the availability of phosphorous, molybdate, borate, and a number of other nutrients.

2.3. Improvement in soil chemical, physical and biological properties

Organic matter helps to bind soil particles together into aggregates. This improves the physical properties of the solid making it easier for roots to penetrate. Tillage becomes easier and soil becomes well-drained. The binding effect also reduces wind and water erosion. With organic matter, the water retention capacity of soil is also considerably increased.

2.4. The nitrogen cycle vis-a-vis organic matter

This brief description of the organic matter was provided to put the discussion and review on nitrogen into proper perspective, because organic matter in soil is the reservoir of nitrogen, and nitrogen is the most important of the nutrients that affect crop yields. Other nutrients like phosphorous and potash are also important when growth rates are fast, but even for this the presence of nitrogen is required. Micro nutrients have their own roles but are required in smaller amounts.

The following review will focus on nitrogen. General constitution of phosphorous and potash wiil also be reviewed in fresh wet, sun dried slurries and slurry composts in the latter part of the chapter.

Nitrogen exists in two main forms in the soil. The major portion of it, usually more than 90%, is present in an organic form, immobilized in the amines and other complex molecules that make up soil organic matter. This ' organic nitrogen pool' represents a substantial store of nitrogen. It is unavailable to plants, but is protected from being leached away when it rains. Only a small fraction of the total soil nitrogen exists in soluble forms that can be used by plants, either as nitrate or ammonium ions. Thus rather than the total nitrogen content of any organic matter, the proportion of these ions determine crop growth.

The processes through which nitrogen is gained or lost in the soil forms a cycle known as the nitrogen cycle7 ( Fig 1). Organic matter break-down constitutes one of the key pathways in this cycle. As the organic matter decomposes in the soil a portion of nitrogen in the organic pool is released into solution (mineralisation).

It has been estimated that 2.3% of the total organic nitrogen pool is mineralised each year (Brady 1974, cited in Barnard et al., 1985). The soil also receives small amounts of nitrogen from rain and dust. Other important sources include the biological nitrogen fixation and, of course, nitrogen fertilisers. Nitrogen losses from soil occurs through uptake by crops, leaching and soil erosion. A certain amount is also lost in a gaseous form, either due to the action of ' denitrifying bacteria' which converts nitrates to nitrous oxide and nitrogen, or through the volatilization of free ammonia. The former is of relatively minor significance; the latter is only important in dry, alkaline soils which have been treated with large amounts of urea or ammonia fertiliser (Barnard et al., 1985).

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Figure 1. Nitrogen Cycle In Farm Land

Source: Adapted from Gunnerson and Stuckey, 1986, reproduced in GATE, 1993:

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2.5. Nutrient composition of biogas slurry in different forms

2.5.1. Overview of past research on anaerobic digestion

The production of combustible gas ('Marsh-gas' or * Will-o' the Wisp') from decaying organic wastes in marshes and swamps has been known for a long time (Acharya, 1961:2). Laurie (1941) reported that as early as 1778 Volta knew that the gas contained methane. Poppof in 1875, produced hydrogen and methane from a mixture of river silt (mud) and materials containing cellulose (APRBRTC, 1983:1). Martin-Leake and Howard (1952) reported that Louis Pasteur in 1884 presented a paper (by Gayan) on the production of methane from yard manure. Also early in 1866, Bechamp, a student of Pasteur, was among the first to show definitely that the formation of methane was a process of biology (APRBRTC, 1983:1) According to Waksman (1932), Omeliansky in 1902 pointed out that cellulstic material like filter paper if inoculated with horse-dung or river mud, along with mineral salt solutions and kept under anaerobic conditions, evolution of gas took place. This gas mainly contained methane and hydrogen. Thysen and Bunker (1927) reported that Omeliansky also isolated two different types of bacteria: Bacterium methanigenes which produced methane and Bacterium fossicularum which produced hydrogen. In fact he was the first to isolate methanobacteria (not a pure strain though) in 1916 (APRBTC, 1983:1). In the beginning of the Twentieth Century, the method of anaerobic fermentation or "digestion" was successfully applied by sewage chemists (Acharya, 1961:2). In 1936, using chemically synthesized media to culture, Barker obtained a kind of microorganism capable of producing alcohol, butanol, and propanol through fermentation (APRBTC, 1983:1). A considerable amount of research work was carried out by sewage chemists on different aspects of the digestion process and sludge digestion plants were installed at Birmingham, Baltimore, Mogden and Bombay; the gas produced was used for operating machinery and for lighting purposes (Haseltine, 1933 quoted by Acharya, 1961:2) and even for operating lorries and tractors (ibid.)- However as Acharya (1952) reported, the application of the method to the materials, other than sewage sludge, did not receive required attention. Such an attention for him was important since huge quantity of farm waste could be utilized for gas production. In this context the studies of Foroler and Joshi (1923) (anaerobic fermentation of newspaper, filter-paper, banana peels, etc.); Keefer et al. (1934) Fair (1934) (anaerobic digestion of garbage), Nelson et at. (1939 ; 1940; 1942); (digestion of chopped corn stalks, chopped seed-flax, artichoke, etc.), and Desai (1945) (cattle dung and vegetable litter), are important. The works of Duceliar and Isman (1949), Duceliar (1950), Isman (1950) (all on farm wastes), among many others, were important since combustible gas was successfully produced in all those experiments. The works of Desai (1945; 1964), Patel (1951) and Acharya (1953, 1958) are important ones in the Indian context as long as gas production and plant design efforts are concerned.

From this background it is clear that the emphases up to 1950, were clearly on energy (gas). Manurial aspects were generally not taken up as a matter of research. In fact during the course of review it was revealed that the engineering and micro biological aspects of gas production remain a dominant preoccupation to the 1990s.

2.5.2. Early research on manurial value of slurry

By the 1950s many researchers had already reported that manure production by anaerobic digestion was more efficient in nitrogen conservation than aerobic methods (Acharya, 1961:8). Desai and Biswas (1945, cited by Acharya, 1961: 8) obtained manure containing 1.7 percent nitrogen in the dry matter and the manure showed better effect on crops than from yard manure. According to an account furnished by Rosenberg (1952a, cited by Acharya, 1961:4) an experiment was carried out by H. Hisserich in Germany and to discuss it a special conference was held at Ludwigsburg in 1947. As a result of the deliberations in the conference, a large-sized mechanized biological gas plant was set-up at Allerhorp in the Luneberg Health area. The experiment with anaerobicaiiy digested manure showed that it gave higher yields than ordinary farm yard manure. This led Martin-Leake

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and Howard (1952a, quoted in Acharya, 1961:4) to remark: "The Luneberg Health is notoriously one of the most hopeless agricultural tracts in Europe. It is claimed that after four or five years' application of the Allerhorp residual tank manure, the sugar-beet crop compared favourably with what could be grown on the best soils in Germany." The Allerhorp experiments also found that the manure was specially valuable oh light soil like that at Luneberg Health (Germany) and produced good effect on crops like potatoes, vegetables and tomatoes. In order to obtain good quality manure without loss of nitrogen, along with good gas production, the experimenters recommended digestion to an extent of 30 percent of the organic matter or 22.5 percent of the dry matter (Rosenberg, 1952 cited in Acharya, 1961:8).

The earlier days of attributing fertilizing value to biogas slurry (and up to some extend today) was largely based on laboratory studies and isolated observations of crop performance rather than serious research into the nutrient composition of bioslurry in different forms and the subsequent effects on crop performance.

2.5.3. Contemporary research on nutrient constitution of biogas slurry

It is obvious that biogas generation is technically feasible through the anaerobic digestion of a variety of organic materials. In India, China and Nepal, however, animal and human faecal matter are the dominant inputs for the production of biogas. During the anaerobic fermentation process about 25 to 30 percent of the organic matter from the faecal matter is converted into biogas while the rest becomes available as a residual manure (Chawla, 1986) which is generally considered to the rich in major plant nutrients (NPK) as well as in micro nutrients such as zinc, iron, manganese and copper, which are generally in short supply in many soils (Tripathi, 1993:10).

Nitrogen as a fertilizer is consumed in the largest quantity. Therefore its provision through organic sources, residues, chemical fertilizer, is of enormous importance to agriculture. Because of this, its presence both in the animal waste and the digested slurry and the examination of literature on whether loss of nitrogen occurs during the process of anaerobic digestion for obtaining combustible gas is of direct relevance to the study. In India (Acharya 1961:1 5) has reported that during the process of anaerobic fermentation of bullock dung, about 1 5 percent of the total nitrogen contained in the dung converted into the ammoniacal form and that almost the whole of the ammonia formed remained in solution in the digested slurry. Acharya (1961:17-18) has also reported the results of another set of experiment that measured the formation of ammonia during anaerobic digestion of bullock dung. The experiment showed that digested dung slurry contained 12 to 18 percent of its total nitrogen in ammoniacal form. The pH measurement carried out on the digested slurry showed values ranging from 8.0 to 8.4.

Acharya (1961:17) also reported that on drying the digested cow dung slurry, around 96 percent of the dissolved ammonia escaped into the air. In order to explain this loss a measurement of pH before and after the fermentation was made and was found to be 7.2 and 8.3 respectively. The increased alkalinity was presumed to be due to the accumulation of ammonia in the slurry after digestion. Due to the alkaline pH, almost the whole of the ammonia present was lost by volatilisation during the evaporation and drying of the digested slurry* (Acharya, 1961:17; Chawla, 1984:109). The dried residue contained only 1.78 percent of nitrogen. If there was no loss of ammoniacal nitrogen, the total nitrogen would have come to around 2.16 percent of the dry matter.

In another experiment Acharya (1961:17) again found that during the sun drying operation, the manure lost nitrogen roughly equivalent to the whole of free ammonia present. Analysts of the residue left after sun drying showed only very small recoveries of ammonia.

The nutrient constitution of biogas slurry vary from site to site. And the factors affecting this constitution range from the type of fodder being eaten by the livestock to the type of organic biomass fed to the digester. Table 3 and 4 present examples of variations in the constitution of

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various materials used in the digestion.

Table 3: Total solid content (dry matter) of fermentation materials commonly used in rural areas (approximation)

Materials Dry matter content (%) Water content (%) Dry rice straw 83 17 Dry wheat straw 82 18 Maize stem 80 20 Green grass 24 76 Human excrement 20 80 Pig dung 18 82 Cow Dung 17 83 Human urine 0.4 99.6 Pig urine 0.4 99.6 Cow urine 0.6 99.4

Source: APRBRTC, 1983:46

Table 4: Carbon: nitrogen ratio of feedstock commonly adopted (approximation]

Feedstock Carbon content of feedstock by weight (%)

Nitrogen content of feedstock by weight (%)

Carbon: Nitrogen ratio (%)

Dry wheat straw 46 0.53 87:1 Dry rice straw 42 0.61 67:1 Corn stalk 40 0.75 53:1 Dead leaves 41 1.00 41:1 Soybean stalk 41 1.30 32:! Grass 14 0.54 27:1 Peanut Stalk and leaves 11 0.59 19:1 Fresh sheep dung 16 0.55 29:1 Fresh cow dung 7.3 0.29 25:1 Fresh horse dung 10 0.42 24:1 Fresh pig dung 7.8 0.60 13:1 Fresh human dung 2.5 0.85 2.9:1

Source: APRBRTC, 1983:45

Reports on nutrients are often vague due to the fact that researchers often do not bother to mention the sources, methods and modes of analysis. It is thus usual not find whether a particular nutrient data were generated on volume/volume or weight/weight or dry/dry basis. Table 5 to 1 7 below present a glimpse of the nutrient composition of different forms of organic manure as reported by different authors. Different authors report different data based on their circumstances. The data presented below are not exhaustive and are meant to provide a " feel' of the situation.

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Table 5 : NPK values of fresh cow dung slurry

N% P2O5% K2O% Author 1.00-1.80

(1-4) 0.8-1.2

(2) 0.8-1.00 (0.9) Gupta, 1991

1.5-2.0 (1.75)

1.0 1.0 Tripathi, 1993

1.30 0.82 1.07 Gupta, 1991 1.25-1.30

(1.28) Chowla, 1986

1.51 Naear. 1975 in Kuppuswamy, 1993 1.8-1.9 (1.85)

Acharya, 1961

1.4-1.8 (1.6)

1.1-2.0 (1.55)

0.8-1.2 (D

Gitanjali et al. in Gupta 1991

1.30-2.50 (1.9)

0.90-1.90(1. Myles et al., 1993

1.4-1.8 (1.6)

1.0-2.0 (1.5)

0.8-1.2 (t.0)

DOST, Govt of India, 1981

1.5-2.0 (1.75)

1.0 1.0 Khandelwal et al., 1986

0.5-1.0 (0.75)

0.5-0.8 0.65 0.6-1.5 (!.05) Demont et al, 1990

Figures in parenthesis indicate average

Table 6 : Composition of spent slurry from nightsoil biogas plants

N% P% K% Author 3.25 1.00 0.83 Kaulet-al;, 1986

3.0-5.0 (4.0)

2.5-4.4 (3.45)

0.7-1.9 (1-3)

Khandewai, 1986

Figures in parenthesis indicate average

Table 7: NPK content of sun -dried bioslurry

N% p% K% Author 1.60 1.40 1.20 Gitanjali et. al. in

0.5-1.0 (0.75)

0.5-0.8 (0.65)

0.6-1.5 (1.05)

Demont et al. 1991

1.00 0.23 0.84 Gupta, 1991

Figures in parenthesis indicate average

Table 8: NPK content of bioslurry and FYM

N% P% K% Author Composted bioslurry 0.5-1.0

(0.75) 0.5-0.8 (0.65)

0.6-1.5 (1.05)

Demont et al., 1991

FYM 0.6 0.25 0.55 Gupta, 1991

Figures in parenthesis indicate average

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Table 9 Quality and composition of human faeces and urine*

Approximate quantity Faeces Urine Water content in the nightsoil per 135-270 gram 1.0-1.3 litre capita Dry wt, per capita 35-70 gram 50-70 gram Approximate Composition (Dry Basis) Moisture, % 66-80 93-96 Solids 20-34 4-7 Composition of Solids • organic matter, % 88-97 65-85 • Nitrogen (N), % 5-7 15-19 • Potassium (K), % 0.83-2.1 2.6-3.6 • Carbon, % 40-55 11-17 • Calcium (Ca), % 2.9-3.6 3.3-4.4 • C/N ratio 5-!0 0.6-1.1

Source: Satyanarayana et. al., 1986:11 * Phosphorous Is conspicuously absent in the. report

Table 10: Characteristics of nightsoil

Parameters (Dry basis} Average Values PH 5.2-5.6 Moisture % 86.7 Total Solids, % 13.3 Volatile Solids, % 11.6 • Total Nitrogen (N) % 4.0 • Total Phosphorus (P), % 1.53 • Potassium (K), % 1.08

Source: Sacyanar3yana et. al., 1986:11

Table 11: Manurial value of slurry and other characteristics of human excreta fed to biogas digesters.

Parameters Value Gas production capacity/day 0.025 m3 Methane, % 60-65 Carbon-di-oxide, % 30-35 Hydrogen Sulphide, % 0.05-0.10 Fuel Value, K cal/ m3 5600-6500 Quantity of sludge produced 0.71 Litres wet/capita per day with 5% total solids Manurial value of sludge • Nitrogen, % • Phosphorous, % • Potassium, %

3.25 1.00 0.83

Source: Satyanarayana et. al., 1986:17

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Table 12: Average composition of nightsoil and urine

Item Faeces Urine Moisture (%) 70-85 93-96 Organic matter (% dry wt.) 88-87 65-85 Nitrogen (%) 5-7 15-19 P,O, {%) 3-5.4 2.5-5 K7O {%) 1-2.5 3-4.5 CaO (%) 4.5 4.5-6

Source: Gaur et at., 1986:106

Table 13: Composition of spent slurry from nightsoil biogas plant

Item Percent on dry weigh basis Nitrogen 3.0-5.0 P2O5 2.5-4.4 K2O 0.7-1.9

Source: Gaur, et at, 1986:107

Table 14: Effect of digester manure on physical and chemical properties of Soil

Location Treatment pH Organic Total Total Available Volume Porosity matter nitrogen (P2O5) (P2O5) WL gm/c3 (%) (%) (%) (%) ppm Chyu- 1. Check 6.85 1.040 0.064 0.096 13.2 1.44 45.66 county (2 2. Digester years) Sludge 6.80 1.210 0.068 0.110 14.4 1.41 46.59 3. Increase 0.1 7% 0.004% 0.014% 1.2 -0.03 0.93% Dayi- 1. Check 8.30 1.035 0.071 0.109 16.3 1.27 52.59 County 2. Digester (1 y«r) Sludge 8.35 1.286 0.101 0.1 10 0.04 1.16 57.35 3. Increase 0.25% 0.03% 0.001% 4.1* -0.11 4.76%

Source: APRBRTC, 1983:160 * the increased ppm should have been -16.24 which means that the available P2O5 was reduced with the application of digester sludge in this location. The report is however a preliminary one.

Table 1 5: Comparison of loss of nitrogen between digester manure and farmyard manure

Treatment Total Nitrogen Ammoniacal Nitrogen Jin % Jin % Before treatment 0.950 !00 0.168 100 Digester manure 0.940 98.9 0.438 260.7* Open air pool manure 0.646 68.0 0.138 82.1 Compost 0.572 60.2 0.0301 17.9

Source: APRBRTC, 1983:1 55 i jin= 1/2 kg * Ammoniacal nitrogen increased to 260.7% from 100% in the manure before digester treatment (an increase by more than 1.6 times)

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Table 16: Approximate range of nutrient contents of digester manure

Digester Organic matter (%)

Humic acid (%} Total nitrogen (%}

Total Phosphorus (P2O5) (%)

Total potassium(K2O) (%)

Effluent ----- ----- 0.03-0.08 0.02-0.06 0.5-0.10 Sludge* 30-50 10-20 0.8 -1.5 0.4 -0.6 0.6-1.2

Source: APRBRTC, 1983:155. 'Settled, more solid portion of the slurry Table 17: Average constitution of fresh dung, dung slurry, digested slurry

Table 17: Average constitution of fresh dung, dung slurry, digested slurry*

Fresh dung Dung mixed with water Slurry g/kg % wet

base % dry base

g/2kg % wet base

%dry base

g/2kg % wet base

% dry base

Water 800 80 ---- 1800 90 - 1820 93 Dry matter 200 20 100 200 10 100 140 7 100 Organic 150 15 75 150 7.5 75 90 4.5 64 Inorganic 50 5 25 50 2.5 25 , 50 2.5 Z6 Total Nitrogen 5 .5 2.50 5 .25 2.5 5 .25 3.60 Mineral 1 .10 .50 1 .05 .50 2 .10 1.40 Organic 4 .40 2 4 .20 2 3 .15 2.2 Phosphorus 2.50 .25 1.25 2.50 .13 .25 2.5 .13 1.80 Potassium 5 .50 2.50 5 .25 2.50 5 .25 3.60 Total 1000 100 - 2000 100 - I960 100 -

Source: Van Nes, undated: 4 * Based on calculations

Broad conclusions can be drawn from these tables. Theoretically sun-dried slurry should provide a lower percentage of nitrogen as around 90% of the ammoniacal form of nitrogen is generally accepted to be volatilised during the sun drying process. But as the tables show the data provided from the different sources are not that much consistent. However more of the reports show higher available N content in fresh bioslurry than in sun-dried slurry. Also nutrient content is reportedly higher in the sludge (settled, more solid portion of the slurry) than in the liquid effluent {supernatant, liquid portion of the slurry which collects at the surface). Bioslurry derived from human excreta contains the higher proportion of nitrogen than any form of organic manure reported in these tables. Composted bioslurry is found to contain higher proportions of NPK than FYM Similarly digested slurry also contains higher amount of mineral nitrogen than fresh dung and dung mixed with water. It is also evident that both fresh cow dung and non-digested dung slurry contain higher proportion of organic nitrogen than digested slurry indicating the conversion of organic nitrogen to more available forms during the process of anaerobic fermentation. No differences are evident in the proportion of potassium and phosphorous contents in these three forms of organic fertilizers.

Similarly there are also many reports indicating the superior manurial value of composted slurry over ordinary composts (Demont et al., 1991 inter alia).

A recent report (ATC,1997) on the constitutions of slurry compost, fresh and sun- dried slurry and fresh cow dung by a laboratory in Nepal furnishes the following data:

15

Table 18.a. : Average constitutions of different forms of organic manures from samples collected from different parts of Nepal

Particulars PH Moisture (%)

Total Nitrogen

(%)

Organic Matter

(%)

C:N Phosphorous P2OS %

Potassium K20 %

Remarks

Compost 7.8 2 65.02 1.31 3.75

25.07 71.70

11 11

1.18 3.37

0.88 2.52

Wet basis Dry basis

Sun-dried slurry

7.4 4 40.66 1.73 2.92

24.53 41.46

8 8

0.69 1.17

0.68 1.15

Wet basis Dry basis

Fresh dung 8.1 1 81.25 0.30 1.60

15.47 82.46

30 30

0.78 4.16

0.42 2.24

Wet basis Dry basis

Fresh slurry 7.1 6 93.07 0.06 0.87

4.55 65.66

44 44

0.04 0.58

0.06 0.87

Wet basis Dry basis

Source: ATC, 1997 In brief, following points can be noted in terms of manurial values of these forms of manures as reported in this analysis.

As against the theoretical premise and data from India, estimated NPK values of fresh slurry reported are too low. Also as against so many of the published data, the higher NPK values in sun-dried slurry is difficult to explain. The nitrogen content of sun-dried slurry even exceeds that of the bioslurry compost.

The NPK values of bioslurry compost is excessively high as compared to published data and exceeds those values reported for the fresh slurry in exceptional ways. Higher NPK values of bioslurry compost vis-a-vis ordinary compost or even sun-dried slurry can be explained but the reported values exceed the NPK values of fresh slurry. The data indicate the sun-dried slurry is superior in terms of nitrogen to all the three categories of manure (bioslurry compost, fresh dung and fresh slurry) on wet basis. On dry basis slurry compost is shown to be superior to other forms in terms of nitrogen content. On both dry and wet bases, fresh slurry is shown to fall at the bottom in terms of nitrogen content. This is not only in the case of nitrogen, fresh slurry is also shown to contain the lowest amount of both phosphorous and potassium among these four types of organic manures. These reports cannot be explained on the basis of what has been generally said about the fresh biogas slurry in biogas literature. Perhaps the sampling techniques themselves have to do something with these results. The measurement difficulties in the determination of manurial values of different organic manures have been discussed elsewhere in this review.

ATC (1997) has also reported the results of analysis of samples of chicken dropping, cattle, buffalo and pig dungs collected from various parts of Nepal. Table 18b presents data from this analysis.

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Table 18.b. : Average constitutions of fresh chicken dropping and fresh cattle, buffalo, and pig dung from samples collected from different parts of Nepal

Particulars PH Moisture (%)

Total Nitrogen

(%)

Organic Matter

(%)

C:N Phosphorous P2OS %

Potassium K20 %

Remarks

Cattle and Buffalo

8.11 81.50 0.26 1.41

14.88 80.50

33 33

0.77 4.17

0.39 2.11

Wet basis Dry basis

Chicken 7.35 42.60 2.05 3.57

43.34 75.41

12 12

1.07 1.86

1.0 1.74

Wet basis Dry basis

Pig 7.3 60.15 0.59 1.48

15.64 39.26

15 15

0.89 2.23

I.I 1 2.79

Wet basis Dry basis

Source: ATC, 1997

Table 18b above shows that, as usual, chicken dropping contains the highest amount of total nitrogen. This has shown to be so on both wet and dry bases. Chicken dropping is followed by pig dung in terms of the amount of total nitrogen content. However, on dry basis, both pig and cattie + buffalo dungs showed higher amount of phosphorous and potassium content.

ATC (1997) also analysed fresh slurry samples from biogas plants with and without toilet attachment. Table 18c below presents comparative data on these two types of fresh slurry. Table 18.c. : Average constitutions of fresh slurry from biogas plants with and without

toilet attachment Particulars PH Moisture

(%) Total

Nitrogen (%)

Organic Matter

(%)

C:N Phosphorous P2OS %

Potassium K20 %

Remarks

Without toilet attachment

7.1 2

93.83 0.054 0.875

4.54 73.59

48 48

0.040 0.648

0.066 1.070

Wet basis Dry basis

With toilet attachment

7.2 0

92.32 0.065 0.864

4.555 59.306

40 40

0.039 0.508

0.064 0.833

Wet basis Dry basis

Source: ATC, 1997

In terms of NPK values, no pronounced differences between fresh slurries from biogas plants with or without toilet attachment are observable. This may due to the relatively lower amount of human excreta (as compared to cattle and buffalo dung) fed to the biomass plants.

2.5.4. Nitrification studies and the issues of nitrogen conservation in digested slurry

Table 18d: Nitrification of digested slurry Manure treatment NO] found after

3 months (mg.) Mean value (mg.)

Excess over soil only (mg)

Percentage of added manure N Nitrified

Soil only (duplicate)

6.90 7.50

7.20 -

Soil plus digested slurry (duplicate)

11.25 12.00

11.63 4.43 7.38

Soil plus farm yard manure (duplicate)

10.20 9.90

10.05 2.85 4.75

Soil plus ammonium (duplicate)

21.00 19.50

20.25 13.05 87.00

Source: Acharya: 1961:29

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Acharya's nitrification studies showed that digested slurry was somewhat superior to farm yard manure in regard to its nitrifiability in the soil, a reconfirmation of the conclusion of an earlier (Desai et al. 1945) study of nitrification.

Nitrification studies with similar results is also reported by Chawla (1984) after a couple of decades later.

Table 19.a. : Nitrification of digested slurry

Treatment mg NC3 per 100 g Soil Percent of manure N nitrified Soil 5.3 ... Soil + Wet Slurry 11.7 21.3 Soil + Dry Slurry 10.9 18.6 Soil + Compost 10.2 16.3

Source: Chawla, 1984:110

Table 19 shows that fresh digested slurry nitrified to the extent of 21.3 percent compared to 16.3 percent mineralisation of compost nitrogen. Sun dried slurry nitrified to the extent of 18.6 percent. This has to be so due to the loss of ammoniacal nitrogen. This finding along with Acharya (1961) and Desai et al. (1945) shows the advantage of anaerobically digested slurry and thus provide a sound basis for slurry extension educational programs.

On the whole, these sets of experiments suggest that the process of anaerobic digestion possesses a double advantage, i.e., the process, in addition to providing a good quality manure also supplies a large volume of combustible gas. (Anaerobic fermentation in the biogas digester does not result in any absolute increase in the nitrogen content of the slurry; the relative increase is noticed due to the loss of 25 to 30 percent of the loss of organic matter of the dung during biogas generation (Kate, 1991:9; Gupta, 1991:22). It has been reported that in India the total nitrogen content of the dung rarely exceeds 1 percent due to poor quality of the animal diet, and hence, the nitrogen content usually falls in the range of 1.25 to 1.30 percent. Others have reported slightly different ranges( e.g., Gupta , 1991:18, 1 to 1.8 percent; Maskey 1978:1, 1.6 to 2 percent etc.) These and similar other experiments and arguments compel to believe that anaerobic digestion in general does not reduce the amount of nitrogen.)

Acharya also reported a somewhat contradictory results from experiments conducted in large size plants (1961:35-51). Crop experiments on wheat, sannhemp and marua ( Eleusine coracana) showed that the digested slurry in wet condition did not produce good manurial effect as after sun-drying. The laboratory results discussed above had shown that the digested slurry in wet condition contained about 16 percent of its nitrogen in the form of readily available ammonia whereas the dried slurry contained very little of ammonia and was lower In total nitrogen. It has been suggested that the poorer effect shown by the wet slurry on all the crops examined may be due to some harmful factors to plant growth, possibly H2S or other products of anaerobic digestion, present in the fresh slurry, which are removed in the operation of sun-drying of manure (Acharya, 1961:51). A situation in which wheat yield decreased due to the application of fresh biogas slurry Is also reported from researches in Nepal (Maskey, 1978:3). For reasons unknown, the result has not been properly verified. Sathianathan (1975 quoted by Maskey, 1978:3) has suggested that the high ammonia content of fresh digested slurry could force large dose of N2 in plant and create excessive toxic compounds. For this reason, it has been recommended to use slurry after a few weeks of collection from the digester or compost it by mixing with other substances. The presence in fresh slurry, of toxic compounds like H2S is also mentioned by Balmor et al. (1982:220). But they dismiss it as a serious problem in Nepal because the cattle and buffalo dungs is the common feed for biogas plants

18

and treatment of slurry in such cases should not be a serious concern. Even if nitrogen fixing bacteria have been detected in some systems (El-Haiwagi, 1980), the air-tight, anaerobic environment precludes the possibilities of nitrogen fixation; however nitrogen is increased in the relative sense due to the decomposition of organic matter and formation of gases and not due to formation of "new nitrogen" (Gupta, 1991:22). An increase of total nitrogen is inconceivable since there is not known process on nitrogen fixation' inside the digester (Tarn, et al. 1983:12).

Tarn et al. (1983) and Chawla (1984) are concerned about the 'inflated and exaggerated' reports of increase in nitrogen content in the residual slurry. Tarn et al. also cites lanotti (1979), Institute of Soil and Fertilizer of Sichuan China (1979) and Li (1982) in gathering the challenging evidence against the importance of biogas slurry as fertilizer. Tarn (1983:12) citing these authors states that the "nitrogen level does reduce during anaerobic digestion, and the degree of reduction ranges from 3 to 10 percent". However, no effort is made anywhere in his lengthy report to explain how this amount of nitrogen is lost during anaerobic digestion. Tarn also argues that the evaluation of digester slurry by measuring its nutrient composition immediately after it comes out of the digester is not appropriate since storage time, transport distance and application method etc. have direct effect on a benefit assessment of slurry as fertilizer. Vogtmann et al. (1978) has reported that nitrogen loss of anaerobically digested manure that is ploughed four days after application varied from 15 to 19 percent depending on the climatic condition. This loss can be expected to be higher in the tropics.

Van Brakel (1980) is ambivalent, and at times openly critical, about the logic behind the promotion of bioslurry as a superior manure. He raises some serious questions about the way the manurial value of organic manures, in general, are assessed. According to him the assessment of the quality of fertilizers from organic sources is a difficult task involving the following factors:

• the form in which the manure is available ( liquid content, size of solid particles)

• the way it is distributed in the soil

• the C:N ratio, the C:P ratio, the relative proportion of these two ratios , and the presence of minerals

• the properties of the organic material in the manure, particularly the disposition to mineralize and the amount and type of humic components

• the rain that falls after the manure application

• the temperature and the humidity after manure distribution in the soil which strongly affect microbral activity in the soil (Van Brakel, 1980:103).

Van Brakel argues that even if these factors are supposedly kept under some sort of control, it is virtually impossible to compare different ways of manure processing particularly when processing times of the systems to be compared are different. Because of the variations in the properties of excreta of animals, the manure should be obtained from the same animals at the same time. If the processing time is different, argues Van Brakel, it is impossible to take due account of the factors mentioned above. Together with the statistical fluctuations that are said to be inherent in these kinds of measurements, concludes Van Brakel, " only very large and long research projects may lead to any reliable conclusions for the ' average' situation (p. 103).

He raises a similar problem with the determination and interpretation of the C:N ratio, which is commonly used as a general characteristic of the quality of organic manure, and suggests that even if there is some ground for using this parameter, one needs to be cautious in its application: "other things being equal, the C/N ratio may well have a different physiological effect depending on the way the carbon and the nitrogen are bound. In general it will be positive if the nitrogen is easily accessible (that is to say, that mineralization proceeds quickly. However if the manure contains large

19

quantity of easily decomposable carbon compounds, this may stimulate microbial activity in the soil so much (in particular if it is warm an humid) that no nitrogen is left for the plants, unless the C/N ratio is too low" (ibid). In addition it makes quite a difference at what stage of the manure processing cycle the C/N ratio is determined.

These arguments are directly relevant for those who are involved in assessing the constitution of biogas slurry. In addition to the methodological problem in assessing the manurial values of organic manures, Van Brake!, in line with (Tarn, 1983), is not optimistic about the outcomes of slurry promotion and extension. He believes that "manure processed anaerobically contains a larger amount of nitrogen that is readily assimilated by plants" but the handling of slurry after it comes out of the plant is a major problem in nutrient conservation, and concludes that "for small scale application of anaerobic digestion { in rural areas where the digester should be cheap and simple to operate) there are few possibilities of preventing nitrogen losses, and the alleged better preservation of nitrogen cannot be advanced as an advantage of the anaerobic way of processing manure" (p. 105).

On the whole, these reviews reveal that there is relative increase of nitrogen during the anaerobic digestion. Evidence of nitrogen losses during anaerobic digestion as claimed by some is difficult to find in the literature. Indeed it seems that substantial nitrogen losses occur from the moment slurry is taken out from the digester to the moment it is worked in the soil.

2.5.5. Other nutrients

Up to this stage the review has been mainly centred around nitrogen due to reasons explained elsewhere. However slurry also provides available phosphorous and potassium and micronutrients that are important but are required in smaller amounts. No detailed reviews are necessary on these topics.

2.5.6. Bioslurry and the physical and biological qualities of soil

In addition to nutrient supply, bioslurry and its different forms improve the physical and biological quality of soil. Bioslurry, in its different forms, is relatively free from foul smell, weed-seed and phytopathogenic organisms (Tripathi, 1993). It also improve soil porosity and water holding capacity (moisture retention capacity {Tripathi, 1993; Santosh et al., 1993, APRBRTC, 1983)). Slurry has bulk and fibre to hold soil manure (Arnott, 1982:56). This is what may be called the anti-erosion quality of humus. In addition numerous researchers have reported that soil microbiai activities increase remarkably after bioslurry utilisation. Slurry provides energy to soil microflora including the N fixing and P solublizing organisms (Lakshmanan, 1993:3). Bioslurry is also reported to be free from weed seeds. More weed seeds are killed during digestion than during any other manure processing system( Van Brake), 1980:106) .

Scheffer et al. have reported that 20-30 days is enough to destroy the viability of all weed seeds. It is suggested that the free ammonia that is formed during anaerobic digestion poisons the seeds because methane does not kill the seeds but inhibits their germination. Even if some of the weed seeds remain viable after anaerobic digestion subsequent composting of biogas slurry (specially at thermophilic temperature range) will destroy the viability of these remaining seeds (Price, undated: 137). Weeding is generally an expensive operation in many parts of Nepal where fresh cattle dungs are used. The weed elimination part can be seen as an important labour reducing aspect of bioslurry (even more so if bioslurry is composted) in crop production, although no systematic studies were encountered about this aspect during the review.

Chapter 3 deals with the effects of different forms of bioslurry on crop production.

20

CHAPTER 3

EFFECTS OF BIOSLURRY ON CROP PRODUCTION

3.1. Background to the study of manurial value of bioslurry

A review of works in biogas technology by van Brakel (sub-titled "a critical review of the pre-1970 literature7) published in 1980, stated that "not much work has been carried out on the quality of the solid output of an anaerobic digester in terms of fertiliser value" (van Brakel, 1980:101). This remains largely true even for today if countries like China and India are excluded from the statement. Even in India, the emphasis traditionally has largely been on energy aspects of biogas technology (Singh, 1997, personal communication) as evidenced by the important involvement of the Ministry of Non-Conventional Energy Sources (MNES) in biogas technology development and promotion. Nonetheless, Indian Agricultural Research Institute (IARI), India's premier research institution of that kind has given "occasional attention" to the fertiliser value of cow dung, comparing anaerobic digestion with other types of manure processing (Van Brakel, 1980:101). In fact, IARI is one of the four institutions worldwide cited by Van Brakel in his review of pre-1970 literature on biogas technology, to have "carried out work on a significant scale concerning this important aspect of the evaluation of anaerobic digestion for agricultural waste processing {Van Brakel,, 1980:101) - the others being studies in. the University of Gottingen and Braunschweing- Volkenrode and in countries like Poland and the then USSR. In IARI anaerobic digestion was compared with other types of manure processing. IARI reported that biproducts of anaerobic digestion had narrower ON ratio (25) 3& compared to cow dung from farm yard manure (38) and the former gave better crop yield than the latter. Nonetheless, Van Brakel notes that no general conclusions were reached.

At the university of Gottingen, research was carried out (during the period 1950-55) on various aspects of the outputs of the Atlerhop design when applied to the field. Nitrogen losses and balance of other elements, during anaerobic digestion of manures and various vegetative wastes, were studied. In addition, extent of weed and pathogen destruction during digestion were also studied. Even if the Allerhop process and the manure out of it was positively assessed by many (better availability of nitrogen by plane and relatively narrower C:N ratio than those reported for IARI studies), the results did not seem to warrant any other conclusions than the output of the Allerhop design is comparable to the out come of any other good manure processing system: (van Brakel, 1980:101).

At Branschweig - Votkenrode various designs of anaerobic digesters were studied for their efficiency in presenting nitrogen losses. Field experiments were conducted to determine the quality of the manure.

In Poland field experiments with anaerobically digested manure were carried out but "no definite superiorities of the manure after methane fermentation over ordinary farm manure could be established" (cited by van Brakel, 1980:101).

in the then USSR, the nitrogen assimilation of fermented sawdust was studied and the yield of oats and sweet lupine was reported to have been increased.

3.2. Contemporary research

Although Acharya's (1961) report was examined in the preceding chapter, it is pertinent here to once again discuss the report, especially the experiment on the effect of effect of biogas slurry and FYM on crop production. The premise for doing so is that since "farmyard manure is generally prepared by aerobic fermentation, whereas manure in the fuel gas plant by anaerobic digestion; and the quality of the two products may vary" (Acharya, 1961:50). In a pot experiment, the two manures were

21

applied at the rate of 100 Ib. nitrogen per acre, four weeks before sowing. For comparison, ammonium sulphate was also taken as one of the treatments. The dosage of ammonium sulphate was maintained at 25 Ib. per acre [following Russell, 1950, cited by Acharya, (1961:50) according to whom the availability of nitrogen in bulky manures is considered to be about 25 percent of that in ammonium sulphate. It was an experiment with five replications. Table 19 below presents data from this experiment.

Table 19b: Mean yield/pot of grain, straw of wheat and marua (Eleusine coracona) and Total Dry Matter of sannhemp.

Treatment Wheat Marua Sannhemp

Grain Straw Grain Straw Total Dry MatterNo Manure 8.84 13.46 10.1 31.4 93.4 Digested Slurry in wet condition 10.32 15.26 12.0 33.8 106.8 Digested Slurry in dry condition 11.31 17.39 13.6 36.8 117.2 Farm yard manure 10.02 16.28 12.4 31.6 104.4 Ammonium sulphate 13.70 19.55 15.4 41.2 121.2

Source: Acharya, 1961:51

As was discussed in the preceding chapter, despite the finding that wet slurry which is reported to contain around 16 percent of the nitrogen in the form of readily available ammonia (the dry slurry, on the other hand, contain very little ammonia and lower total nitrogen), and despite the usual claim chat "Maximum benefit is obtained when slurry is used in liquid form as it comes out of plant (Khandeiwal, et al. 1986), the poor effect shown by wet slurry (the phenomenon will also appear in experiments to be reviewed latter), despite the presumed working of toxic materials like hydrogen sulphide and others, is an interesting and relevant area of systematic investigation.

Maramba (1978:155) reports the result of an experiment in the Philippines in which the feedstock incorporated with high percentages of wheat pollard which contained higher phosphorous than either nitrogen or potassium. As Table 20 below shows, the treatment with 388 ml of effluent/1 sq. m of plot showed higher grain yield/plot than either the control or other treatments.

Table 20: Plot fertilizer experiment Maya Farms, Philippines

Treatment Mean Grain Yield/Plot (Grains) Control 479.20 5714ml of Effluent 507.00 388 ml of Effluent 556.17 Ammonium Sulphate + Disodium Phosphate + Potassium Sulphate 542.72 (8 gm- 8 gm - 3 gm)

Source: Maramba, 1978:155

The above table shows that higher dose of effluent here is not superior as compared to the lower dose as long as grain yield is concerned. Studies have shown that (Arnott, 1982; Sathianathan, 20

1978,.etc.) uncontrolled supply of nutrients, especially nitrogen may, depress crop yields. When biogas sludge runs directly into rice fields there is a large increase in the growth of blue green algae. These algae absorb nitrogen from the air, which is good for the crop. But if excessive supply of

22

sludge is not stopped halfway through the growth cycle of the rice, flower initiation is stopped. The rice plants continue to grow, but the rice grains do not develop (Arnott, 1982:62; DOST, 1981:47) reporting on the works done in the Indian Agriculture Research Institute (IARI) states that if slurry is not dried, there is very little loss of nitrogen. There is also no loss of phosphorous, potassium and other micronutrients. Mineralisation of organic nitrogen in liquid slurry is also reported to be superior to that in sun-dried slurry and farmyard manure. (This is in line with the earlier studies of Deshai and Biswas, 1945 and that of Acharya, 1961). The relatively lower nitrogen mineralisation in sun dried slurry is attributed to poor dispersion of colloidal material resulting to increased resistance to subsequent microbial decomposition Table 21 below presents data from the pot experiment conducted at the IARI.

Table 21: Mean yield of rice (grain) and berseem (dry fodder)

Treatment Average of first three years (yield: g/pot}

Average of next two years ( yield: g/pot)

Rice Berseem Rice Berseem

Wet Slurry Dried Slurry Farmyard Manure

20.4 24.4 21.9

18.4 23.1 22.8

11.8 12.9 11.7

14.4 15.0 14.2

Source : DOST, Govt. of India, 198 1:4

Again as in Acharya (196 I), Maskey (1978), wet slurry shows poor performance as compared to dried slurry despite the evidence that mineralisation of organic nitrogen in liquid slurry is superior to that in sun dried slurry and also that most of the nitrogen in ammoniacal form is lost when fresh slurry is sun dried.

3.2.1. Research in slurry utilization in crop production in Nepal

In Nepal, the first biogas plant was introduced by Father Saubolle, S.]. of St. Xavier's School as early as 1955, serious thoughts were given only after the newly set up Energy Research and Development Forum of Tribhuvan University recommended that biogas be considered as alternative energy resource for Nepal (Fulford, 1985: 1.5-1.6). This resulted in the inclusion of biogas programme in the Agriculture Year of 1975/76. Study of effect of slurry on crop production was initiated at the Division of Soil Science and Agricultural Chemistry in Khumaltar, and by 1978 a couple of preliminary reports came out {Maskey, 1978; Bhattarai et al., 1978). The experiments were conducted in wheat and it was indicated that fresh effluents caused toxic effects on wheat crop (Fulford, 1978:19 and personal communication with concerned researchers). Maskey (1978) conducted a simple experiment to see the effect of dry and fresh biogas slurry on wheat yield furnishes the following data:

Table 22: Effect of biogas slurry (dry and fresh on wheat yield)

Treatments Grain yield in kg/ha. Increment over (Average of 3 Years) control kg/ha., I. Control 1288 — 2. Biogas Slurry (Dry) 1450 162 3. Biogas Slurry (Wet) 1842 554 4. 50% dry Slurry +

50% Chemical fertilizer 2706 1418 5. 75% dry Slurry +

25% Chemical Fertilizer 1744 456

6. Chemical Fertilizer 3503 2215

Source: Maskey, 1978:2

23

The table shows that biogas slurry was not superior in terms of its manurial value as compared to either different combination of dry slurry and chemical fertilizer or chemical fertilizer alone. Dry slurry showed the lowest increment in wheat yield, probably indicating the loss of nutrient during the drying operation.

Maskey (1978) also reports the result of another experiment where the effect of biogas slurry on wheat yield was compared with the effect of other locally available manures.

Table 23: Comparison of the effects of biogas slurry*and other manures on wheat yield.

Treatments N% P2O s% K2O% Grain yield kg/ha Increment (Average of 3 yrs) {kz/M Control - - - 1550 Biogas Slurry 1.49 2.94 2.38 1783 233 Compost .93 .75 .50 2015 265 Poultry Manure 2.6 1.26 1.66 3782 2232 Fertilizer - - - 3301 1851

Source: Maskey 1978:2 * Although it is not explicitly mentioned in the report, implicitly, it seems to be fresh slurry

The table shows that the biogas slurry was not able to achieve higher incremental wheat yield as compared to compost and poultry manure. Poultry manure, in fact gave the highest incremental yield (even higher than that of chemical fertilizer). The researcher comments: "From these simple field trials our observations do not confirm with the results other scientists found in other parts of the world. There may be several factors which were not looked upon in detail during these trials.... "(Maskey, 1978: 2). Although this particular experiment did not furnish information on the form of slurry used, the possible toxic effect of biogas slurry, presumably in its fresh liquid from, is noted (Maskey, 1978:3), though the claim of toxicity is not verified by further research in Nepal. As mentioned elsewhere, even if toxicity of fresh dung biogas slurry has been noted by a number of authors abroad, Bulmer et at. (1985) note that this should not be a matter of concern in Nepal.

Besides wheat, the effects of biogas slurry (it used to be called "gobargas" slurry due to "gobar" or dung being a predominant feedstock for biogas plants) on the yields of a number of crops were studied (Maskey, 1978:3). The table below summaries the incremental yields of these crops.

Table 24: Effects of biogas slurry on paddy, tomato, cauliflower, French bean, wheat, and maize

Yield t/ha Crops Without slurry With slurry

Increment

Paddy Tomato Cauliflower French Bean Wheat Maize

2.7 15.0 4.6 0.3 1.2 1.7

3.0 17.8 5.6 1.0 1.8 2.7

0.3 2.8 1.0 0.7 0.6 1.0

Source: Maskey {1978:3)

It can be noted that all crops gave higher yield with biogas slurry. Again the report did not mention the form of digested (fresh liquid slurry, wet slurry, dried slurry, residual sludge) of slurry and the type of feedstock fed to the biogas plant. In addition, the report is silent about the mode of experiment. If as in Tarn's argument (1983) "without slurry7' was meant to be without any kind of manure, then one is not sure whether or not such increment could also be achieved by other manures. In this sense, the experiment is meaningless.

24

In another experiment, Bhattarai (1978) reports that biogas slurry when "applied directly" "depressed" wheat yield in Bhairahawa Agriculture Station, while such a "depressing effect" was not observed in Khumaltar. She noted that the effluent probably was not fully decomposed. In order to look into these matters, an experiment was designed for irrigated and rainfed condition incorporating 5 treatments (control, wet slurry, dry slurry, 50% dry slurry + 50% chemical fertilizer and chemical fertilizer (usual dose). The crop was wheat (RR 21). The data are presented below:

Table 25: Effect of biogas slurry on wheat yield under irrigated and rainfed conditions

Treatment Irrigated (yield:kg/ha) Rainfed (yield:kg/ha) 1. Control 1450 1450 2. Dry Slurry 1750 1600 3. Wet Slurry 1560 1750 4. 50% Chem. Fertilizer

+ 50% Dry Slurry 3800 2750 5. Chemical Fertilizer

(Usual Dose) 5700 4200 Source: Bhattarai (1978:2)

Earlier it was reported that wet biogas slurry had higher manurial value than that of dry slurry as long as wheat crop was concerned (Maskey, 1978). But the manurial value of slurry was reported to be lower than that of compost. The data on the above table show that dry slurry gave better wheat yield than wet slurry under irrigated condition. Under rainfed condition, wet slurry gave higher yield than dry slurry. It is probably due to the fact that wet slurry also provides moisture which is an important factor in rainfed condition. As usual, the chemical fertilizer and the combination of chemical fertilizer and dry slurry gave far more higher yields than slurry in wet and dry forms.

Again, the incorporation of compost, as one of the treatments in the experimental design, could have provided a realistic picture, as the purpose generally was not to compare yield with chemical fertilizer but with other sources of organic manure.

Bhattarai and Maskey (1988) also reports the result of research on the effect of azotobactor inoculation in the different sources of organic manure including biogas slurry on the grain yield of wheat at Khumaltar Agronomy Farm.

Table 26: Effect of azotobactor inoculation of biogas slurry and other compost manures on

wheat yield Treatment N-P-K

(kg/ha) Year Grain yield of Wheat

(kg/ha) Increment

(kg/ha) Percentage increment

With Aiotobact

or

Without Azotobactor

Control

-40-30

1976 1977 1978 Mean

2325 1550 930

1603.33

2569 1162 930

1553

54.00

3.771

Biogas Slurry

100-40-30

1976 1977 1978 Mean

2650 2400 1300

2116.66

2850 1700 1080

1876.66

240.00

12.788

25

Poultry Manure

100-40-30

1976 1977 1978 Mean

3175 2112 1600

2295.66

2350 1537 1450

1779.00

516.66

29.042

Compost 1976 3300 3025 100-40-30 1977 5065 5117 1978 3980 3730 Mean 4098.30 3957.33 141.00 3.563 Fertilizer 1976 ------ 2625 100-40-30 1977 ------ 4287 1978 ------ 2930 ------ ------ Mean ------ 3280.66

Source: Bhactarai and Maskey (1988:81-85)

Azotobactor inoculation in biogas during with 100-40-30 chemical fertilizer gave a mean wheat grain yield of 2116.66 kg/ha. This is lower than that given by poultry manure and far lower than that given by compost both with azotobactor inoculation with the same amount of chemical fertilizer.

These few researches on the manurial value of biogas slurry in Nepal provide a confusing array of signals on the superiority and inferiority of biogas slurry over other organic manures. The superiority of compost demonstrated so far goes against the argument that nutrient, especially nitrogen, preservation is better in anaerobic digestion and that aerobic composting is inferior in this kind of nutrient preservation. A number of points should be noted in this context. These researches were not well designed. Different forms of slurry have different levels of nutrient contents. In most cases, the experiments did not even mention the form of slurry used. In addition, the time span between the removal of slurry from the digester and its ultimate use in the experiment is not mentioned in all of these experiments. Nutrient loss can occur in this time span. Furthermore, the method of application is important. For example, if slurry is left in the field exposed for a long time without ploughing or without covering by soil, significant amount of nitrogen is lost. The storage practice is similarly important. An exposed slurry pit is obviously not desirable from the point of view of nutrient conservation. "Stilt worse, comparing the yields oV wops appftfcd *«Wh dlgestM %ffVa%Tii *Mfah tVitat crops non. rettfctag vttf form ctf fanflhgr fc practically meaningless" (Tarn, 1983:13). Research into the effect of biogas slurry on crop production has a long way to go. The research works initiated in Nepal in the mid-seventies failed to get momentum; and after few insignificant reports, research activities in this area ceased to exist within a couple of years.

3.2.2. Research in slurry utilization in other countries

In Poland, Kuszelewski et al. compared anaerobic and aerobic manure processing and found that, beyond any doubt, anaerobic digestion reduced nitrogen loss, and nitrogen was more easily assimilated. However in both pot and field experiments no difference in yield was found (cited in Van Brakel, 1980:105). Van Brake! reports that the farmers' reports maintained in, Italy, France, and a number of tropical countries are favourable with respect to the manurial qualities of anaerobic sludge. However he suggests that % there may be some bias in these reports7 (ibid). His critical perusal of the yield reports compels him to say: " .. it is doubtful whether any significant differences in crop yield between various manure processing methods have been established' (ibid). He opines that "as far as there are any differences, one may expect that they are different for different boundary conditions and different crops, because of the interrelated influence of the presence of nitrogen, phosphorous, and other elements, coming out differently for different crops" and cites the reports of Sen et al. in which yield reportedly improved in pea but not in rice. "This may be explained with reference to the amount of available phosphorus in the soil and the extent to which nitrification will occur in the soil" (p.106).

Cott (1984) reports that mushrooms, cucumbers, tomatoes, when grown in the digester solid, did not provide good growth medium the first year, but the following year, yields were surprisingly high.

26

Cott noted that this could substantially reduce investment in anaerobic digestion by shortening pay-back time. This could also reduce fertiliser costs and costs involved in post-anaerobic treatment of slurry in addition to neutralizing costs for peat.

Although earliest documented attempts to develop biogas technology in India can be traced back to the early 20th century (1900-1920) (Moulik, 1990:11), concerns with slurry utilization for crop production is a relatively recent development. Large scale slurry study programmes began only after the 1980s. Dhussa (1985:25-29) compiled the results of some of the experiments, conducted up to the mid-eighties, on the effects of biogas plant effluent on the yield of rice, wheat, maize, cotton, cucumber, tomato, mungbean, and sunflower.

Table 27: Comparison of the effect of effluent and FYM on the yield of rice, maize, wheat, and cotton

Yields: kg/ha Incremental yield Crop Digester Effl t

FYM Kg % Rice 634.4 597.5 38.9 6.5 Maize 555.9 510.4 45.5 8.9 Wheat 450.0 390.5 59.5 15.2 Cotton 154.5 133.5 21.5 15.7

Source: Idnani et al., 1974, cited in Dhussa, 1986:1 1 4

The effluent application gave higher yields in all the crops under consideration. The difference between biogas effluent and FYM was manifested in a comparatively more pronounced way in the case of wheat and cotton yield.

Table 28: Comparative yields of cucumber for varying quantities of effluent vis-a- vis chemical fertilizer

Treatment Average yield/pot (kg) Control A (No manure or fertilizer) 3.70 Control B (Recommended quantity of fertilizer) 6.78 Slurry @ 5t/ha 3.20 Slurry @ 1 Ot/ha 4.57 Slurry @l5t/ha 7.36 Slurry @20t/ha 6.20

Source: Clarita et al., 1982, cited in Dhussa, 1986:1 14

The cable shows that biogas slurry applied at the rate of 15 t/ha gave the highest grain yield, higher even than the recommended dose of chemical fertilizer.

Table 29: Comparative effects of different doses of slurry and slurry-chemical fertilizer combinations on tomato production

Treatment Yield: t/ha % Increase over C t lControl 26.12 -

Fertilizer @ 90-120-60 kg/ha NPK 61.02 133.61 Slurry @ 5 t/ha 34.34 31.47 Slurry @ 10 t/ha 37.69 44.29 Slurry @ 1 5 t/ha 40.53 55.17 Slurry @ 20 t/ha 42.74 63.63 Slurry @ 5 t/ha + NPK @ 45-60-30 kg/ha 47.33 81.20 Slurry @ 10 t/ha + NPK @ 45-60-30 kg/ha 47.53 81.97 Slurry @ 15 t/ha +NPK @ 45-60-30 kg/ha 49.12 88.06 Slurry @ 20 t/ha + NPK @ 45-60-30 k?/ha 54.56 108.88

Source: Clarita et al., 1982, cited in Dhussa, 1986:1 14

27

Half dose of fertilizer with 15 and 20 t/ha gave relatively higher yields, but then, these yields were out-performed by the treatment with full dose of chemical fertilizer.

Table 30: Effect of biogas slurry with and without mineral fertilizer on mungbean yield

Treatment Computed Yield % Increase over (kg/ha) Control Control 764.77 - NPK @ 30-60-0 kg/ha 921.50 22.25 Slurry @ 5 t/ha 756.75 0.25 Slurry @ 10 t/ha 780.38 3.38 Slurry @ 1 5 t/ha 774.38 2.60 Slurry @ 20 t/ha 875.25 15.95 Slurry @ 5 t/ha + NP @ 15-30 kg/ha 796.12 5.46 Slurry @ 10 t/ha + NP @ 15-30 kg/ha 820.50 8.70 Slurry @ 15 t/ha + NP @ 1 5-30 kg/ha 821.25 8.80 Slurry @ 20 t/ha + NP @ 15-30 kg/ha 869.25 15.14

Source: Clarita et al., 1982, cited in Dhussa, 1986:1 15

The above table presents data on yields of mungbean obtained from various levels of effluent alone and with half the recommended quantity of NPK. The comparison of these yields with that obtained from the application of full dose of NPK shows that the effect of low level of effluent application is insignificant. The treatment with 20 t/ha of effluent with or without NPK has given the same yield . "It may be concluded that the leguminous crops don't respond well to the application of manures" (Dhussa, 1985:26). However, as wifl be seen in other experiments, leguminous crops like peas also did well with bioslurry.

Table 31: Effect of biogas slurry with and without mineral fertilizer on sunflower yield

Treatment Computed yield: kg/ha % Increase over control

Control 1773.33 - N @ 120 kg/ha 3233.33 82.33 Slurry @ 5 t/ha 2426.67 36.84 Slurry @ 10 t/ha 2206.67 25.00 Slurry @ 1 5 t/ha 2573.33 45.11 Slurry @ 5 t/ha + N@ 60 kg/ha 2706.67 52.63 Slurry @ 10 t/ha +N @ 60 kg/ha 2226.57 25.55 Slurry @ 1 5 t/ha + N @ 60 kg/ha 2646.67 49.24

Source: Adapted from Clarita et al., 1982, cited in Dhussa, 1986:115

In sunflower, the use of biogas slurry alone in various doses and the combination of the same doses with N @ 60kg/ha gave lower yields than the treatment with N @ 120 kg/ha. However, even the lowest dose of (5 t/ha) gave yield that is 36.84% higher than the control. If the potential of biogas slurry as organic manure is noted at this point (Dhussa,!985:26), it should also be noted that farmers would probably put other organic manures in their sunflower field. In that case, it is illogical to attribute superiority in the absence of comparison with other organic sources.

Tentscher (1986) reports the result of one of the studies in slurry utilization in crop production in Thailand in which digested pig manure was compared with chemical fertiliser for the yield performance of vegetable, maize, mungbean and morning glory. The diluted pig manure contained about 0.4%

28

and 0.04% total nitrogen. Effluent was applied as top dressing throughout the growth. The amount of nitrogen supplied through the effluent was 50%, 100%, and 200% of nitrogen in chemical fertiliser. Chemical fertiliser was applied at the rate of 124-52-124 kg/ha for vegetable corn, mungbeans, and morning glory respectively. The treatment supplying 100% N in effluent gave significantly better performance and was at par with chemical fertiliser. For mungbeans, increasing application did not increase the yield significantly--a finding which was also reported by Dhussa (1985) in India {reviewed earlier), though experimental design and treatments varied in these two studies. The yield performance of the treatment with 50% N was as good as chemical fertilizer. In the case of morning glory, plant height increased significantly with the treatment involving the supply of 100% and 200% N, but it was significantly more so at 200% N ( at par with chemical fertiliser).

Koglevi (1987) reports on an agronomical field trial at the Centre National Agro-pedologie in the west African nation of Benin. The purpose of the trial was to study the influence of bio digester effluent on tomato, capsicum, lettuce and cauliflower. Table 30 below presents data from this trial.

Table 32: Average yield (t/ha) of vegetables with mineral fertilizer and effluent application

Treatments Tomato Capsicum Lettuce Cauliflower Control 2 4 26 23 Mineral Fertilizer 13 6 56 36 Effluent @5 t/ha of 22 12 130 48

Source: Kogtevi, 1987:1 The table above shows the superior manurial value of bio digester effluent over control as well as the treatment involving chemical fertiliser.

In an experiment carried out in Peru (Vargas, 1986) during 1983-85 with biol (liquid portion of biogas slurry) and biosol (solid sludge) on alfalfa and maize, it was found that biol as well as increased yield in these crops by more than 25%.

Studies conducted by Sukhadia University of Udaipur, India (1986 Annual Report, Cited by Gupta, 1991:24) reported the following changes in N.P.K levels in soil after slurry application.

Table 33: Changes In soil NPK levels after slurry application NPK at various depths (%) N P K Before Slurry Application After Slurry Application

0.I32-0.I38 0.156-0.236

0.145-0.166 0.145-0.190

0.870-0.885 0.870-0.880

Source, Gupta, 1991: 25

Both N and P content of the soil increased after slurry application. The same university also compared the effect of various fertilisers on the yield of cabbage, mustard and potato.

29

Table 34: Effects of various fertiliser combinations on the yields of cabbage, mustard, and potato

Percentage increase Treatment Cabbage Mustard Potato 1. Control 2. Farmyard Manure 3. Slurry 4. Slurry + Single Super phosphate 5. Slurry + Rock Phosphate 6. Slurry + Potash 7. FYM + Phosphate

----- 18.67 20.63 20.70 15.9 24.9 -----

----- 25.80 45.75 49.75 35.25 ----- 33.98

----- 25.33 34.75 ----- ----- ----- -----

Source: Gupta, 1991:25

Gupta (1991:25-26) also reports the results of 15 demonstrations launched during the Khariff, 1988 under the National Project on Biogas Demonstration through Foundation for Rural Recovery and Development. Table 35 below presents data from these demonstrations.

Table 35: Effect of slurry on the yield of different crops in India (Khariff, 1988)

Crop No. of demonstration % increase in yield over control plot Rice 8 28.87 (Average) Tomato 2 70.5 (Average) Chillies 1 0 Brinjal 1 74.00 Bajr3 1 33.00 Maize 2 56.75 (Average) Cabbage 1 20.00 Potato 1 34.74 Urad I 67.00 Groundnut 1 25.00

Source: Adapted from Gupta, 1991:26 40.98

Overall percentage increase in yield from crops treated with biogas slurry came around 40%. The application of biogas slurry manure gave best results in vegetable crops such as tomato and brinjal followed by crops like maize and urad. Percentage increases in crops like bajra, rice, groundnuts were modest. In case of chillies, there was no increase at all.

According to Singh (1990: 125), the increase in yields was considered substantial for, practically, there was no extra cost for the fertilizer material used. Among the eight Indian states in which these l demonstrations' were conducted, the response was better in dry areas with low soil fertility levels and in which doses of inorganic fertilizer used were low. These states included Andhra Pradesh, Madhya Pradesh, Orissa, and South Bihar.

The responses were moderate in irrigated wet areas with higher doses of fertilizer application such as in the Punjab, Madhya Pradesh, Haryana and North Bihar. Singh (1990:125) and Gupta (1991:26) note that those conclusions are based on scanty data and should not be considered as conclusive. The inferences to be drawn are not to be considered as conclusive but as indicative of an hypothesis for detailed experimentation and further scrutiny by the scientific community (Singh, 1990 :125).

On the other hand Singh (1991:1-2 and personal communication) also notes that biogas slurry manure demonstration cannot be a very scientific agronomic experiment; these are, and ought to be, simple on- farm farmer participatory trials in which farmers can see for themselves an assess the performance in yields.

30

During the Rabi season of 1988-89, one hundred slurry demonstrations were conducted in ten Indian states, namely, Andhra Pradesh, Bihar, Haryana, Kerala, Madhya Pradesh, Maharastra, Orissa, Punjab, Tamil Nadu , and Uttar Pradesh (Singh, 1990: 125). Of these the results of 82 demonstration are presented in the following table (the results of the remaining eighteen demonstrations were either not received or discarded for various reasons).

Table 36: Effect of biogas slurry on crop yield in the Indian States (Rabi, 1988-89) Crop T.N., A.P.,

Kerala Orissa M.P MR Bihar Punj &

Haryana U.P Total

CN (2)22% -- -- -- -- -- -- (2)22%Maize -- -- -- -- (1)16% - - (1)16%Millets (1)100% {1 )42% (1)14% -- -- ~ (1)6.5 {4)40%

POL -- (2)19% -- -- -- -- - (2) 19%PUL (4)11% ~ (1 )20% -- -- -- -- (5)15%Rice (6)43% -- -- -- -- -- - (6)43%VEC (2)30% -- -- -- -- -- -- (2)30%WHT — — (6)20% -- {19)21% (10)21% {25)22% (60)21%

(15) (3) (S) -- (20) (10) (26) (82) GN-Groundnut; PUL -- Pulses; V EG -- Vegetable; WHT -- Wheat; TN -- Tamif Nadu; Pot.-- Potato A.P. -- Andhra Pradesh; M.-- Madhya Pradesh; U.P.--Uttar Pradesh; Punj.-- Punfab Figures in parentheses indicate the number of demonstrations. % indicate the percent yield increase in demonstration plot over control plot. Millet includes jawar, ragi, and oats. Pulses include blackgram and green gram Source: Singh (1990:126)

The average works out to be 23.6% (the table is not clear about how this figure can be arrived at, because a simple averaging gives a couple of percentage points above this figure). Nonetheless, it can be seen that the average incremental yield in Rabi crops is modest as compared to the earlier report of Kharif crops (40%). Singh argues that since Rabi crops in most places are cultivated in irrigated and relatively more fertile lands, the response is less impressive compared to Kharif crops. It is still a substantive increment (Singh, 1990:127)

Biogas slurry also substantially invigorates plant growth in terms of root and shoot growth and the general bulkiness of its vegetative parts. Gupta (1991:24) provides the following comparative data on the effect of different types of manures and fertiliziers on growth of manures and fertilisers on growth of tomatoes and chillies.

Table 37: Effect of different types of manures and fertilisers on the growth of tomatoes Age of

plants (days) Root length Shoot length (cm.) Dry plants wt. (mg.) control SDS FYM CF control SDS FYM CF control SDS FYM CF 10 2.8 5.8 4.5 3.9 7.4 11.2 9.8 8.2 29 183 48 36 20 3.2 6.2 5.5 10.3 8.6 13.4 12.2 10.3 42 262 107 48 30 4.1 7.8 7.2 11.2 9.3 16.2 14.2 i.2 50 506 195 105 40 4.8 9.2 8.6 12.5 10.2 17.8 16.5 12.5 58 912 357 182

SDS- Sun-dried slurry; FYM- Farm yard manure; CY- Chemical fertilizer Source: Gupta (1991:24)

Except on the root length (from 20 to 40 days in which chemical fertiliser bettered), SDS showed better performance, in shoot growth and plant weight (dry) than control, FYM, and chemical fertiliser in all the growth stages (in terms of the given number of days).

31

Table 38: Effect of different types of manures and fertilisers on growth of chillies Age of plants Root length Shoot length (cm.) Dry plants WL Inc.) (days) control SDS FYM CF control SDS FYM CF control SDS FYM CF 10 5.3 7.6 7.1 6.2 8.9 12.6 11.8 10.2 40 130 53 4820 6.1 7.8 7.8 7.1 9.6 14.2 12.6 11.8 56 340 107 5230 6,9 10.8 8.2 7.8 10.3 15.3 15.5 12.6 66 462 134 9840 7.5 12.6 7.8 8.0 11.2 16.9 17.0 13.8 72 868 213 252

SDS- Sun-dried slurry; FYM-Farm yard manure; CF-Chemkal fertilizer Source: Gupta (1991:24)

Despite some of the experimental results reviewed earlier, SDS out performed control, FYM and chemical fertiliser in all the three categories of plant growth (root length, shoot length and dry plant weight) in all the four growth stages (number of days).

In India, from the mid-1980s, the Ministry of Non-Conventional Energy Sources (MNES) launched a country wide "demonstration" programme in farmers field through state agencies, Gujrat State Fertiliser Co-operative (GSFCI, India Farmer's Fertiliser Co-operative (IFFCO), Regional Biogas Development and Training Centres and Voluntary Organisations like FORRAD (Tripathi, 1993:11). By 1991, over 3000 slurry demonstrations' were conducted all over India.

Two plots of equal size were shown with the same crop. Biogas slurry was applied in only one plot ("demonstration" plot) at the rate of 10 tones per hectare in irrigated and 5 tones per hectare in non-irrigated areas. Both plots were given uniform packages of other agronomic practices i.e. fertiliser, seed rate, irrigation, pesticides etc. On maturity, crops from both the plots were harvested and yields compared. Table 39 below provides a summary of results of the demonstrations conducted between 1984-85 to 1991-91 by state agencies from the Indian states of Haryana, Himanlchal Pradesh, Kerala Karnataka, Madhya Pradesh, Gujrat, Goa, Punjab, Uttar Pradesh and Tamil Nadu. These states by themselves represent a number of agro-climatic zones and soil type. By 1991, over 3000 slurry demonstration were conducted all over India at the initiative of the Ministry.

Table 39: Summary of results of slurry1 demonstrations conducted by concerned state departments/agencies in India (1984-85 to 1990-91)

Crop No. of demonstration Over ail average of % increase in crop yield in slurry treated plot over untreated plot

Paddy 88 31.95 Wheat 127 24.69 Maize 14 40.46 Millet 4 40.46 Turmeric 1 27.05 Potato 5 30.85 Chillies 2 24.25 Tomato 3 126.10 Groundnut 8 23.99 Banana 3 4.69 Brinjal 4 103.23 Sugar cane 2 6.29

1 The two major reports (Singh, 1991:1-8 and Tripathi, 1993:11-14) from which this table was compiled do not indicate the form of biogas slurry (fresh slurry, slurry compost, sun-dried slurry) used in these demonstrations. Singh (1993:12) does not mention it in his 'materials and unshod' portion of the report. In the concluding part he has mentioned that "As far as possible wet slurry should be utilized to in the field to avoid loss of ammonia". It seems rather a suggestion and it still is not clear as to what form/s of biogas slurry were used m these demonstrations.

32

Mulberry 1 25.00 Pulses 5 15.00 Mung I 10.40 Bajra 4 35.10 Lady's Finger ! 66.60 Mustard 2 23.00 Jute 1 50.00 Deccanhemp 1 50.00 Tapiaco 1 10.40 Ragi 8 27.00 ]awary J 8.30 Urad 2 34.20 Pea 14 60.18 Total 252 35.94 Source: Singh, 1991:8; Tripathi, 1993:13

The demonstration areas represent various agro-climatic zones, and variations in percentage increase in these zones can be seen as obvious. Even if Singh concludes (Singh, 1991:2) that the overall percentage increase in yield due to slurry application is around 30% the above table gives the figure around 36%. Singh argues that this result alone justifies the acceleration of National Project for Biogas Development in India.

The Gujrat State Fertiliser Corporation (GSFC) also conducted demonstrations on a variety crops during 1989-90. Table 40 below provides a summary of results of these demonstrations.

Table 40: Summary of results of demonstrations on the effect of biogas slurry* on crop production (GSFC, India, 1989-90)

Crop No. of demonstration Over all average of % increase in crop yield in slurry treated plot over

untreated plot Paddy Maize Wheat Groundnut Jawar Bajra Gram Mustard Tobacco Castor Cotton Green Gram

4 4

51 7 2 8 3 3 2 1 4 3

10 18 15 18 21 15 15 11 13 3

18 22

Total 92 14.91 Source: Tripathi, 1993: 13 * The summary report does not state the form of slurry used

Overall percentage increment in all these demonstrations can be seen as widely fluctuating. This has to be so because of the variations in agro-climates, nature of feed stock, types of animal feeds, slurry storage and handling, etc. Nonetheless, yield increments are reported in most of the crops in which demonstrations were conducted.

The large scale demonstration program conducted by FORRAD, GSFC, and state agencies/departments throughout India showed an overall average increase of 24.2 percent on a national basis. Except for some, most of the cases have shown good incremental yield.

33

In addition to increased crop yield, some of the positive observations made during the field demonstrations are summarised as follows:

• Improvement in quality of produce. For example, the size of vegetables like cabbage, • tomato, potato, Brinjal, etc. were significantly increased • Reduction of weed in biogas slurry plots • Biogas slurry does not attract insert breeding • Reduces the usage of chemical fertilisers. This indirectly helps in reduction in unit cost • of produce. • Biogas slurry has high water holding capacity which helps rainfed crops • Seeds treated with biogas slurry have better germination rate • Biogas slurry contains larger amount of organic matter and free ammonia than available • in compost manure, but free ammonia is lost if slurry is dried in the sun • Biogas slurry is ready for use in the shortest possible time • If nightsoil and cattle urine is added, N and P2OS availability in biogas slurry is • strengthened (Tripathi, 1993:14)

As in many other recommendation (See also Kijne, 1984:105 inter alia), Tripathi also concludes that as far as possible wet slurry should be utilised in the field to avoid loss of ammonia. However it should be noted that fertilisation directly following digestion will hardly take place since fertilisation of crops is tied to special application periods {Kijne, 1984:7; Demont et al., 1990:12). Thus storage of wet slurry is an important issue and will be covered separately. Furthermore, research into the 'yield depressing effect' of fresh slurry (Acharya, 1961; Maskey, 1978 inter alia) due to excessive nutrient supply (Arnott, 1986; Sathianathan, 1975 inter alia), or due to H2S and other toxic effects, is far from being conclusive. If these experiments have revealed the yield depressing effects of fresh wet slurry, time and again the application of the same is recommended. Thus, the effects of various concentrations of wet slurry along with toxic effects, the nature of feedstock, etc., needs further research.

Singh et al. (1995:4-1) report on another series of experiments on the effects of biogas slurry on crop production which were conducted under the aegis of the Renewable Energy Sources Research and Development Programme of Che All India Co-ordinated Research Project (AlCRP) on Renewable Energy Source for Agriculture and Agro-based industries. Twelve research Centres spread over in different agro-climatic regions of India participated in this relatively long term R and D activities. Table 41 presents data on optimum level of slurry application in various crops along with yield.

Table 41: Summary of the evaluation of manurial value of biodigested slurry for various cereals and other crops in different agro-climatic zones in India

s. N.

Agrocli made region

Soil Type

Crop Variety Optimum level of N substitution through slurry (%)

Year Grain (q/ha)

Yield Centre/ Institution

Opt treatment

Control (SO F100)*

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10}1. 1 Red

LoamPotato Kufti Jyoti 100 1992 279.0 235.0 HPAU,

Palampur2. II Sandy

LoamWheat Sonalika 25 1990 31.3 24.4 AAUr Jortiat

Maize NLD Composite

50 1992 At par 100 %N

with Urea AAU, Jortiat

Paddy Mansuri 75 1989 25 24.3 IR-50 1990 21.3 21.7

Culture-I 1989 9.1 11.6 3. VI Sandy

loamWheat HD-2329 50 1990 47.0 46.3 IARI, New

Delhi 1991 24.1 24.4 Sandy

loamWheat HD-2329 50 1990 54.9 65.6 PAU,

ludhiana Sandy

loamWheat Sonalika 50 1989 25.5 25.4

34

Fine loamy

-dto- -dto- 25 over and above 100% N thro' urea

1992 26.9 25.4 IAR!, New Delhi

50 1992 28.3 25.4 -dto- Sandy

loamMaize Ganga-5 40 1986 44.88 43.8

1987 28.6 29.6 Sandy

loamPaddy PR-106 40 1987 90.4 74.8 PAU,

Ludhiana

4. VllI Clay (Vertisols)

Wheat Sonalika 75 1988 50.1 45.8 CEAE, Bhopal

1980 43.1 40.3 1990 40.1 39.6 Soybean Durga 75 1988 1.5 23.3 1989 18.8 M 1990 18.4 15.8 Sandy

loamWheat MACS-9 1988 35.6 36 RAJAU,

Udaipur Mustard 60 1988 22.9 22.5 5. IX Medium

blackWheat MACS-9 60 1984 14 14.2

6. X Clay loam

Maize Ganga-5 50* 1986 50.2 51.7 TNAU, Coimbatore

Regi OH 50 1086 32.5 31.7 Slack

soilSorghum Hybrid 50 1987 59.4 52.8 UAS,

Dharwad CSH-5 1988 31.3 34.4 Maize Ganga-5 50 1989 21.7 21.8 Chilly Bydagi 25 1991 53.2 36.2 1992 34.4 39.4 1993 28.6 25.5

50 + Azospirillum culture ICM 1001 (Biofertilizer)

1993 40.4 25.5

7. XI Sandy loam

Paddy Moti 60 1990 47.5 48.7 CRRI, Cuttack

8. XII Red loam

CN 50 1989 25.1 26.6 SPCW, Courtallam

Brinjal MDU-I 50 1992 23.8 21 Source: Singh et al., 1 995:14 *Slurry=O: Chemical fertilizer = 100kg/ha GN : Groundnut AAU: Assam Agricultural University CIE: Central Institute of Agricultural Engineering HPAU: Himanchal Praddesh AgriculturaJ University IARI: Indian Agricultural Research Institute PAU: Punjab Agricultural University R.AJAU: Rajasthan Agricultural University TNAU: Tamil Nadu Agricultural University UAS: University of Agricultural Science, Dharwad, Kamataka

The grain yield data showed that 50 percent of nitrogen requirement of wheat crop (HD-2329, Sonalika and MACS-9) could be met through slurry application in sandy loam soil of agro-

35

climatic region-VI and medium black soil of region IX (Delhi, Ludhiana, Pune) respectively without affecting grain yield significantly. The same level of nitrogen substitution through slurry also showed for maize (Ganga-5 and NLD Composite), ragi (Co-11) and sorghum (Hybrid CSH-5) in clay loamy/black soils of region X and groundnut crop in red soil of region XII (Coimbator, Dharwad and Courtallum). Additional dose of nitrogen through chemical fertiliser resulted in slightly higher grain yield of wheat (Sonalika) under fine loam soil of region VI (New Delhi): Root density showed marked increase with the addition of slurry through chemical fertiliser as compared to control. Around 75 percent of nitrogen need of wheat (Sonalika) and soybean (Durga) was met through slurry in clay (vertisols) soils in region VIII (Bhopal), no significant reduction in grain yield was observed. The same level of nitrogen substitution was found for paddy crop (Mausuri, R-50, Culture-1) in region II (Jorhat, Assam). Biogas slurry met 60 percent needs of wheat, mustard and paddy (Moti) in Udaipur and Cuttack. Around 40 percent nitrogen substitution through slurry application was found to be optimum for maize (Ganga-5) and paddy (PR-106) in sandy loam soil of New Delhi and Ludhiana. Slurry could, however, meet only 25 percent of nitrogen needs of wheat (Sonalika) and Chilli (Byadagi) In sandy loam soil of Jorhat, Assam and black soil of Dharwad, Karnataka respectively. Addition of azospiriilum culture (ICM100I) at 50 percent slurry substitution in chilli (Byagdi) in black soil of Dharwad, Karnatak improved yield level by 58 percent. Biogas slurry was able to meet complete nutrient requirement of potato crop (Khufri Jyoti) in Palampur, Himanchal Pradesh.

Although reviews of research in the application of biogas slurry in seed treatment will be taken up separately, it is pertinent here to note that this series of experiments also included seed treatment with biogas slurry. Soaking of wheat seeds (HG 2380) for 6-12 hours in slurry and water before sowing resulted in significant increase in germination percentage at Palampur, Himanchal Pradesh. In addition, mean germination time is reduced and the root length of seedlings increased. In Dharwad Karnataka, application of slurry stimulated beneficial microbiological activities in respect to fungi, phosphorous solublizer and nitrogen fixing azotobactor (Singh, et al., 1995:15)

Kanthaswamy (1993) reports the result of studies on effect of biogas slurry on rice carried out in farmer's field in a village in Kanyakumari in South India. The soil was wet, black loamy and the rice variety used was TPS I. Table 42 below presents data on grain and straw yield for the different treatments followed.

Table 42: Effect of biogas slurry on rice grain and straw yield in South India Treatments Grain Yield % Increase Straw Yield % Increase kg/ha over control kg/ha over control T1— Control 3546.06 _ 6070.29 - T2-FYM 12.5 t/ha 4304.84 21.37 5298.85 -12.70 T3-BGDS 5 t/ha 4368.07 23.18 5109.16 -15.83 T4—BGDS 10 t/ha 4722.1 7 33.16 5298.85 -12.70 T5-BGDS 15 t/ha 5316.56 49.92 5551.78 -8.54 T6-BGDS 10 t/ha+ 25% NPK 4873.93 37.43 5172.39 -14.79 T7—BGDS 10 t/ha+50% NPK 4810.70 35.66 6500.26 7.08 T8—BGDS 1Ot/ha+75%NPK 5000.40 41.01 7195.82 18.54 T9-BGDS 10 t/ha+ 100% NPK 4809.44 35.62 7828.14 28.95 T10-FYM 12.5 t/ha + 25% NPK 4808.17 35.59 5425.32 -10.60 T1 1-FYM 12.5 t/ha+50%NPK 4241.61 19.61 5045.92 -16.87 T12-FYM 12.5 t/ha+75% NPK 4873.93 37.44 5678.25 -6.45 T13-FYM 12.5 t/ha+ 100% NPK 4431.31 24.96 6247.34 2.91 T14-NPK 100% 4115.15 16.04 6120.87 0.83

FYM-Farmyard Manure; BGDS-Biogas Digested Slurry Source: Adapted from Kanthaswamy, 1993:46

Interestingly, application of BGDS alone at T5 (15t/ ha) recorded maximum yield (5316.56 kg/ha) and it was at par with T12 (FYM I2.5t/ha +75%NPK--4873.93 kg/ha), T8 (BGDS10t/ha-h 75%

36

NPK--5000.4 kg/ha), and T6 (BGDS 10t/ha +25% NPK--4873.93 kg/ha). The control recorded the minimum yield (3446.06 kg/ha). The results have also shown that the application of BGDS in combination with fertilizers like urea, superphosphate and muriate of potash give higher grain yield than when these fertilizers were applied alone. On the whole, these data on rice production showed that the application of BGDS significantly influenced the grain yield and that the highest grain yield was obtained by applying BGDS @ 15t/ha.

The earlier studies by Laura and Idnani (1972), Sankaran et al.r(1981) and Sankaran and Swaminathan (1988) reported the same trend in grain yield in their respective experimental crops (Kanthaswamy, 1993:46)

Maximum straw yield was recorded in T9 (BGDS 10 t/ha +100% NPK--7828.14 kg/ha) followed by T8 (10 t/ha + 75% NPK--5045.92 kg/ha). This showed the effective combination of inorganic fertilizer and BGDS in straw yield. Sankaran and Swaminathan( 1988) also reported the same trend in Maize (Kanthaswamy, 1993:47).

Keyun et al. (1990:25) reports a successful case of biogas slurry utilization from Dongxu village, Jinagsu Province in China. According to the report, biogas fertilizer was applied to 106 hectares of fertile fields for six successive years. Soil organic matter content raised to 2.7% in 1988 from 1.3% in 1982. The grain yield doubled. Compared to the year 1982 the amount of chemical fertilizer application dropped by 86% The report, however, does not mention the amount and form of bioslurry used) . The net income per hectare was reportedly four times higher than in the neighbouring villages that did not use biogas fertilisers.

For China as a whole, Karki et al.( 1995:2) report the 'average growth rate' of various crops and vegetables2 as given in the following table.

Table 43: Effect of biogas slurry in crop yield in China Crops Incremental Yield {%) Wheat + 13.60 Com + 16.90 Rice + 9.40 Rape seed + 1.90 Cotton + 20.20 Sweet potatoes + 18.80 Vegetables + 25.00 Source: Karki et al., 1 995:2

On an average 10-20% increase in yield has been reported for China.

The APRBRTC (1983) reports the results of field experiments conducted in 16 counties in Sichuan province of China. The experiment involved comparison of effects on crop yield of digester effluent and open air pool manure. Table 44 below presents the summary of results.

2 The meaning of the expression 'average growth rate' is not clear, for in technical usage, growth rate express temporal dimensions, and the report does not mention the year for which the average growth' rate was calculated. If the report meant average annual incremental yield due to slurry application, the mention of the year would have been helpful. No source is cited for further clarification

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Table 44: Comparative effects of digester effluent and open air pool manure on crop yield

Yield (jin/mu) Increase Number of Crops D.E Check jin* / mu** % Tests

Rice 634.4 597.5 38.9 6.5 18 Maize 555.9 510.4 45.5 8.9 9 Wheat 450.0 390.5 59.5 15.2 29 Cotton 154.5 133.5 21.5 15.7 2 Rape 258.4 233.6 21.8 106 15

Source: APRBRTC, 1983: 156 D.E. Digester effluent * I jin equals 1/2 kg ** I mu equals 0.667 ha.

The above table shows an average incremental yield of 14.6%. Based on these data it has been concluded that "the digester effluent is better than open air pool manure regardless of the kinds of soils and crops" (APRBRTC, 1983:156).

Air dried digester sludge is also reported to have increased soil fertility and crop yield in China. Table 45 below presents data on this respect.

Table 45: Effect of digester sludge on crop yield in China Crops Amount of D.S. applied Yield {jin*/mu**) Number of tests (jin/mu) D.S. Check jin/mu % Sweet potato 2250 3236.0 2863.0 373.0 13.0 Rice 2000 871.9 798.9 73.0 9.1 Maize 3000 667.5 617.7 49.8 8.3 Cotton 3000 166.6 154.3 12.3 7.9 D.S-Digested sludge I jin equals 0.5 kg I mu equals 0.667 ha. Source: APRBRTC, 1 983:1 56

The air-dried digested sludge on the average increased yield by approximately 10% over the control as compared to about 15% in the case of digested effluent. The application of digester effluent in combination with ammonium bicarbonate [ (NH4)HCO3] has increased crop yield and soil structure that are deteriorated as a result of continuos use of large doses of fertilizer in China. Table 46 presents data on the increased crop yield by the application of such a combination.

Table 46: Effect of digester effluent + (NH4) HCO3 on the yield of rice and maize in China Rice Maize

Yield (jin/mu)

Increase Yield (jin/mu)

Increase

Treatment

jin/mu jin/mu %

Check 696.7 - - 566.7 - --

Digester effluent @4500 jin/mu 736.6 39.9 5.7 677.3 106.0 18.8

(NH4)HCO3@20iin/mu 736.0 39.9 5.7 620.2 53.3 9.4

Effluent @ 4500 jin/mu + (NH4)HCO3@? jin/mu

781.3 84.6 12.1 780.0 213.3 37.6

Source: 1 jin equals 0.5 kg 1 mu equals 0.667 ha. Source: APRBRTC, 1983:158

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As the table shows, the combination of chemical fertilizer and digester effluent substantially increased the yield of both rice and maize.

Based upon the analysis of these results and depending upon the crops, soil types and agro-climates 25-100 percent replacement of chemical fertilizers with bioslurry has been recommended in India.

Singh et al. (1995) reports the results of study on the effea of biodigested slurry for raising pea (Pisum sativum L), okra Abelmaschest esculentus L.), soybean (Glycine max L.) and maize (Zea mays L.) in the hilly condition of Kangra district in Himanchal Pradesh (Alt: 5O0-5500m arnsl).The experiments were conducted in the areas located between 900 to 1300 m amsl with four treatments and five replications.

Table 47: Details of the study pertaining to comparative effect of different fertlizers on pea, okra, soybean, and maize in Himalchal Pradesh, India S.N. Crop Variety Soil Area (m2) Treatment

1 Pea Linkon Sandy Loam

500 T,= Farmers practice (10 FYM and 19.32 kg N/ha) T2 * Recommended dose of fertilizer {10 TFYM, 25 T3 = iO T biogas digested slurry, 25 kg N, 60 kg P and K/ha T4 =12.5 T Biogas digested slurry, 60 kg P and K/ha

2 Okra Pusa Sawani

Silty Loam 360 T,= Farmers practice (6 FYM and 48 kg N/ha) T2 = Recommended dose of fertilizer (10 TFYM, 72 kg.N, 50 kg P and K/ha) Tj = 5 T biogas digested slurry, 72 kg N, 50 kg P and K/ha T4 = 12 T Biogas digested slurry, 50 kg P and K/ha

Soybean Shivalik Silty Loam 1000 T,= Farmers practice (10 FYM and 16.25 kg N/ha) T2 = Recommended dose of fertilizer (20 TFYM, 20 kg. N, 60 kg P and 40 kg K/ha) T3 = 10 T biogas digested slurry, 25 kg N, 60 kg P and 40 kg K/ha T4 = 12 T Biogas digested slurry, 60 kg P and 40 kg K/ha

4 Maize Himvijaya Sandy Loam

1400 T,= Farmers practice (10 FYM and 70 kg N/ha) T2= Recommended dose of fertilizer (10 TFYM, 25 T3 = 10 T biogas digested slurry, 25 kg N, 60 kg P and K/ha T4 = 12.5 T Biogas digested slurry, 60 kg P and K/ha

Source: Singh et al., 1995:5 The doses of NPK were applied according to the recommended packages of practices for the respective crops. The crop yields were analyzed for critical difference (CD) at 5 percent level. Table 48 presents data on yield pod/cob size and plant height.

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Table 48: Effect of biogas slurry on pod/cob size, plant height and yield of pea, okra, soybean and maize

S.N Crop Treatment Average length of pod/cob (cm)

Average plant height (cm)

Yield (q/ha)

1 Pea T1 T2 T3 T4 CD. (5%)

8.58 8.83 9.25 8.10 ----

73.10 74.85 76.92 72.26 ----

88.60 105.6 125.6 76.80 12.68

2 Okru T1 T2 T3 T4 CD. (5%)

8.68 9.45

11.27 8.36 ----

73.34 75.13 78.81 72.56 ----

105.78 114.54 130.10 96.74 8.03

3 Soybean T1 T2 T3 T4 CD. (5%)

4.15 4.50 5.00 4.10 ----

88.43 96.26 98.43 68.03 ---r-

22.00 26.00 29.60 20.40 3.70

4 Maize T1 T2 T3 T4 CD. (5%)

18.14 19.86 21.46 18.05 ----

160.58 165.12

176.51 1 59.54 ----

19.10 22.42 29.17 18.80 2.45

Source: Singh et al., 1995:5

As the table shows, all the crops under consideration gave highest yield in the treatment, T3 where balanced amount of biogas slurry was used with chemical fertilizers, T, (farmers' traditional dose) is deficient in organic and inorganic fertilisers, T4 has complete NPK dose but release of nitrogen is slow at critical growth period because the major portion of N was supplied through biogas digested slurry - the reasons for low yield in T,, and T4. In case of maize, okra and soybean, the yields under T, was at par with T4j but in pea, the yields were significantly higher at T, and T4. In all the crops under trial, balanced fertilizer dose with FYM (T2 and balanced dose with biogas digested slurry (T3) gave significantly higher yield than T,

in all the crops, the yield corresponded with plant height and length of pods/cobs. The total nitrogen dose in T4 was in the form of biogas digested slurry. In this form total amount of nitrogen was probably not available to the crops at critical stages due to its slow rate of release. The next crop might have received the residual effect; to look into this aspect was not the purpose of this experiment.

The report concluded that biogas slurry is a better organic manure than farmyard manure for obtaining higher yield in pea, okra, soybean and maize. In comparison to the farmyard manure, biogas slurry if used along with recommended dose of chemical fertiliser, can give better crop production. Thus biogas slurry was concluded to be a superior manure for raising crops than farm yard manure (Singh, 1995:7).

Kologi (1993: 20-22) reports the results of the experiments on the effects of biogas slurry conducted in different locations in North Karnataka. Experiment and check plots of equal (one acre each) size from fairly uniform soils (red, medium black and black soils) were laid out. The scheme for the experiment was as follows:

Treatment (T): Application of biogas slurry @ 10 t/ha three weeks before sowing along with

recommended dose of fertilizer. Check (C): Application of recommended dose of fertiliser only.

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The data are presented in Table 49 below. Table 49 : Comparative effects of chemical fertilizer and biogas slurry + chemical fertilizer on various crops, North Karnataka, India

Crop Variety Year of expt Yield {kg/ha) % increase Expt. plot Check

Groudnut Dh-8 1985 3000 2250 33.34 Groudnut TMV-2 1988 2500 2000 20.00 Sunflower Morden 1987 1000 875 14.20 Sunflower BSH-1 1991 1650 1375 20.00 Sunflower A-1 1987 750 600 25.00 Cowpea C-152 1987 875 687.5 4.50 Cowpea C-152 1988 300 250 20.00 Hy. Cotton DCH-32 1985 2375 2125 11.76 Hy. Cotton DCH-32 1988 2000 3 500 33.30 Hy. Cotton DCH-32 1987 2500 2000 25.00 Wheat HD-2189 1987 3000 2500 20.00 Wheat HD-2189 1991 1850 1300 42.31 Source: Kologi, I 993: 21

In Groundnut, the yield increased in the range of 20 to 33 percent (average: 26.27 percent) and the pod number per plant ranged from 60 to 70 as compared to 45 to 55 in the control, Sunflower showed an incremental yield of 25 percent. The plants from the treatment plot was1 also reported to be healthier and taller than those from the control plots. Incremental yield in Hybrid cotton ranged from 11.76 to 33.33 percent with an average increase of 23 to 35 percent. Cowpea showed an incremental yield of 20-24.5 percent (average: 22.25 percent). In sunflower the increase in yield ranged from 14.2 to 20 percent (average: 17 percent ). Better crop growth, better head size and intense green colour of the plant was reported in the treatment plot.

On the whole incremental yield ranged from 1 1.76 to 42.31 percent for all the crops under trial. The average increase of 24 percent is similar Co the national average of yield increment due to biogas slurry as reported by Tripathi (1993:14). The highest increase in yield was observed in wheat and groundnut, followed by sunflower. Kologi et al. (1993:22) note that yield increased due Co application of biogas slurry irrespective of the types of soil in the trial plots.

Most studies have thus reported some combination of biogas slurry with chemical fertilizer to be more effective over FYM and chemical fertilizer. A survey of farmers opinions and perception about the use of biogas slurry in a village in Uttar Pradesh reported the following finding:

"With HYV seeds, productivity is in the order: slurry + chemical fertilizer> Heap Manure + Chemical fertilizer (Santosh et al., 1993.37)"

Field investigations were carried out in two phases at Annamalai University experimental farm, Annamalainagar, Tamil Nadu, India (Kuppuswami et al. 1993:15-19) to study the effect of slurry and gypsum enriched biogas slurry on rice and succeeding blackgram (Vigna muneo). In the first phase, the direct residual effects of plain gypsum enriched biogas slurry were compared with farmyard manure. In the second phase plain gypsum enriched slurry along with three levels of NPK were tested. Table 50 and 51 below present data from these experiments.

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Table 50: Direct and residual effect of bio-digested slurry on rice and blackgram Rice Blackgram

Treatment details Tiller number hill -1

Panicle number m-2

Grain yield t ha -1

Straw yield t ha -1

Pod number plant -+

Gram yield Kg ha -1

Wet bio-digested slurry @ 10 t ha-1

6.83 384 7.46 13.03 9.21 422

Dried bio-digested slurry @ 10 t ha-1

7.08 385 7.80 13.69 8.94 383

Wet bio-digested slurry @ 10 t ha-1 with gypsum 50 kg ha-1 (1:0.025)

7.58 413 8.41 15.25 9.12 402

Farmyard manure @ 10 t ha-1

6.58 341 7.33 12.58 10.22 463

Farmyard manure @ 10 t ha ' with gypsum 50 kg ha -1

(1:0.025)

7.26 385 8.00 14.69 10.1 1 431

Gypsum 50 kg ha-1 6.33 330 6.78 11.54 7.83 294 Control 6.17 324 6.61 1 1.03 7.70 292 CD (P=0.05) 0.22 0.06 0.19 0.49 1.24 51

Source: Kuppuswamy et al., 1993:16

Table 51: Effect of plain and enriched slurry on rice-blackgram cropping system

Rice Blackgram Treatment details Tiller number hill -1

Panicle number m-2

Grain yield t ha -1

Straw yield t ha -1

Pod number plant -1

Gram yield kg ha-1

Control 8.36 332 3.2 5.60 22.33 586 IOO:50:5O:kgNPKha -1 10.37 363 4.56 7.20 32.68 988 Biogas slurry @ 10 tha-1 9.16 347 2.93 6.46 26.64 762 Biogas slurry + 100:50:50: kg NPK ha -1

12.00 384 5.11 7.96 37.42 1 196

Biogas slurry 75:37.5:37.5 kg NPK ha-1

1 1.66 381 5.06 7.76 36.86 1175

Biogas slurry + 50:25:25 kg NPK ha -1

11.36 379 4.96 7.68 35.94 1170

Gypsum enriched biogas slurry + 100:50:50:kg NPK ha -1

13.63 408 6.14 8.85 42.92 1283

Gypsum enriched biogas slurry + 75:37.5:37.5 kg NPK ha-1

13.94 411 6.23 9.05 43.68 1295

Gypsum enriched biogas slurry + 50:25:25kg NPK ha -1

1.87 396 5.66 8.49 42.06 1279

Gypsum enriched biogas slurry @ 10 + ha-1

9.56 350 4.03 6.68 228.16 787

100:50:50kg NPKha1 + 500kg gypsum ha -1

10.48 361 4.53 7.16 32.91 1011

CD (P=0.05 0.84 3.7 0.10 0.22 2.52 30.86

Source: Kuppuswamy, 1993:18

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Table 50 above shows that biogas slurry at 10 t ha-1 enriched with gypsum 250 kg ha-1 gave an additional grain yield of 1.80 t ha-1 compared to the control. Gypsum enriched biogas slurry had a clear edge over slurry alone. The residual effect of FYM on the succeeding blackgram was comparatively better than that of biogas slurry. Table 51 shows that gypsum enriched biogas slurry in combination with 75% recommended NPK registered maximum grain yields in rice-blackgram cropping system. Based on these findings it was concluded that the basal application of gypsum enriched biogas slurry holds promise as a viable agronomic practice for the realization of higher yields in rice-blackgram crop-sequence and the maintenance of soil fertility (Kuppuswamy etal., 1993:19).

A field trial on a number of vegetable crops and wheat was conducted in AlEgarh in India for studying the comparative efficiency of biogas slurry and chemical fertilizer Myles et al., 1993: 42-44). The data are presented in Table 52 below.

Table 52: Effect of biogas slurry and chemical fertilizer on different vegetable crops

S.N. Crops Biogas slurry kg/plot Chemical fertilizer kg/plot

Control kg/plot

1 Tomato 196 230 1402 Couliflower 528 492 3503 Cabbage 177 154 1204 Knol-khoi 859 785 6155 Capsicum 23 25 !96 Peas 19 26 207 Gram 11 13 78 Onion 174 180 1009 Wheat 74 85 55

Source: Myles et. al, 1993:44

Table 52 shows that in most cases biogas slurry is as effective as chemical fertilizer. In addition, it is also reported that the quality of bioslurry applied vegetables were superior in quality. Myles et al. have also worked out a comparative economics of biogas slurry and chemical fertilizer and claim that ' biogas slurry use will out weigh the use of chemical fertilizer' {Myles et al. 1993:44)

From Columbia, South America, Campino (1990) reports the results of the effect of nitrogen from liquid manure, bioslurry and urea on hay, and maize. The tests were conducted in a tropical climatic environment in the region south of Cali at an altitude of approximately 800 meters in which the soil was inceptisol (American classification) or pseudogley (German classification). The annual mean temperature calculated per month was 24 degree centigrade, with only minimal monthly fluctuations. Annual precipitation totaled around 1,700 mm. The tests on crops were begun in 1986. An initial test with large allotments (6.0x0.0 m), which was not repeated, analyzed various organic fertilizers. The object of the study was a three year old grass culture consisting of elephant grass (Pennisetum puporeum) and king grass (Pennisetum hvbridm). The results indicated that liquid manure and bioslurry brought the highest yields. Most importantly, nitrogen from these fertilizers exhibited greatest effectiveness. However, the yields from these trials were lower in comparison to those reported by Duclos (1975) and Pazold (1986) primarily because of the poor phosphorous levels in the soil and irregular distribution of rainfall (Campino, 1990:19)

An Additional test (five repetitions) was conducted to see whether, in fact there were significant differences between the effect of urea and increasing concentrations of liquid manure as well as bioslurry. This test was conducted on a new elephant grass culture that was laid out not far from the first one. The soil was clayey, acidic and deficient in phosphorous (2-3 ppm available to plants. Around 20 ppm would be considered a good supply). Supplemental fertilization @ 75 kg/ha of P2O5 was applied.

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This increasing concentration of liquid manure caused the yield to increase sharply. In contrast the effectiveness of nitrogen decreased sharply as the N concentration increased. The comparison of the three fertilizers also showed that N from urea was the least effective. Bioslurry performed slightly lower than liquid manure.

Campino argues (1990:20) that the varying effectiveness of nitrogen from different fertilizers depends upon the way it is converted in the soil. Three different routes may be taken by ammonia which represents the first compound available to plants from the mineralization of urea or the organic substance. The first route is absorption by plants and microorganisms in the soil; the second is binding with clay minerals. The third route is nitrification. Although nitrification occurs relatively slowly in acidic soils, it is an important aspect of nitrogen conversion in the soil. Nitrification is a strictly aerobic process and hence takes place during drier periods. When there is rainfall anaerobiosis occurs and denytrifying bacteria become active and nitrate is transformed into nitrogen oxide, a process that results in considerable loss of gaseous nitrogen. Gerretsen and Hoop (1957) and Focht (1978) inter alia have estimated that such losses could occur between 100 and 300 kg/ha N per year (Campino, 1990:20-21).

Thus a decrease in the effectiveness of the nitrogen from the fertiliser with a high percentage of ammonium or easily mineralizable compounds as in the care of urea is noted. The slight drop in the effectiveness of the nitrogen from bio-slurry is attributed to the narrowing C:N ratio as a result of anaerobic digestion. The report is silent about what constitutes a ' liquid manure'. Test on Maize

This test involved the following treatments 1. Control (without fertilisation) 2. 75 kg/ha of urea (34.5 kg/ha N) 3. Liquid manure (75 m3/ha + 144 kg/ha N) 4. Bioslurry (1253/ha = 155 kg/ha N)

Monitoring of plant growth in terms of plant heights over a period of ten weeks served as the basis for obtaining information about the availability of nitrogen.

It was observed that up to the third week not much differences occurred between the treatments because of the lower nitrogen concentration in the urea treatment. In the first four weeks, bioslurry treatment emerged as slightly superior to all other treatments. Finally, liquid slurry registered the highest growth rate. If should be noted that once a moist period, the growth of the bioslurry treatment decreased, although the nitrogen content in bioslurry was slightly higher than in liquid manure, it is because the onset of rain fall creates anaerobic conditions in the soil, that along with the high soil temperature promote denitrification with considerable nitrogen losses. Such loses are directly proportional to the availability of nitrogen from the fertiliser (Campino, 1990:21). From these experiments it is indicated that the effect of nitrogen from bioslurry lasts a maximum of six weeks in warm and moist conditions This means that the effectiveness of a bioslurry concentration depend substantially on the absorption rate of the crop in question at the time of application. In hay crops, bioslurry concentration of 20 to 70 m3/ha are reported to be appropriate even if the effectiveness of the nitrogen in higher concentration drops sharply in comparison to lower concentration, observation that broadly correspond with the many slurry dose experiments conducted in India reviewed earlier, and the observations from slurry fertilisation in Germany (Schulz, 1990:7).

Jianmin et al. (1990:28-30) reports from China about an experiment involving the comparative effects of slurry, chemical fertilizer and a combination of both. The mixture consisting of chemicals and slurry produced the highest yield, but the best quality and best health of the plants were achieved after using pure slurry.

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In Egypt, Latif's (1990:275-279 ) research on bioslurry utilization involved, among others, the evaluation of direct and residual effects of biogas manure as a complete substitute for NPK and micronutrients on the yields of cotton, wheat, maize, broadbean, spinach and carrots. The application of biogas manure at the rate equivalent to chemical fertiliser is reported to have resulted in increased yield in these crops as presented in Table 53 below.

Table 53: Effect of biogas manure on crop yield in Egypt Crops Yield Increase {%)Cotton 27.50Wheat 12.50Rice 5.90Broad bean 6.60Spinach 20.60Carrots 14.40Maize 35.70Source: Adopted from Latif, 1990:275-279

An average yield increase of 16.88 % can be discerned in these seven crops.

An experiment was conducted at the Central Luzon University in the Philippines on the effects of manure (compost, night soil and pig-dung) and chemical fertilizer on string bean { Gaur et al, 1986: 108-109). As Table 54 below shows highest yield was obtained when the crop was manured with nightsoil. The yield was further increased when the full dose of fertiliser was added.

Table 54 :Yield of string bean treated with different organic manures and chemical fertilizers

Treatment Yield (kg ) from a 3x5 m. Compost Nightsoil Pig-dung 5 t/ha manure 2.37 3.13 1.93 5 t/ha manure + 60 + 80+100

3.95 4.33 4.09

5 t/ha manure + 30 + 40+50

3.63 3.77 3.44

10 t/ha manure 2.79 3.39 4.70 10 t/ha manure +60+80+100

3.65 3.84 3.53

10 t/ha manure + 30 + 40+50

2.77 3.86 3.46

Source: Gaur el al, 1986: 108-109

This nightsoil and pig-dung used in the treatments were obviously not anaerobically digested. In view of the nutrient preservation, relative increase of available nutrients, crop yield can be expected to increase further after anaerobic digestion of night soil. And this is supported by other field experiments in China involving anaerobically digested spent slurry from biogas plants based on human excreta. These experiments have shown that use of spent slurry from anaerobic digestion of human waste, pig waste and rice straw increased the yield of maize rice cotton and winter wheat by 28.1, 24.7 and 12.4 percentages respectively {Gaur et al., 1986).

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3.2.2.1. Utilization of biogas slurry in seed treatment, insect control and foliar dressing

Seed treatment and disease-pest control is an important aspect of crop production. The review in the following pages will cover some of the research works involving biogas slurry in this aspect of the crop production enterprise.

Seed treatment is a technique of applying needed inputs such as organic, inorganic inputs, biofertilizers and pesticides on the seed themselves in an effort to provide a self-sustaining seed unit with an improved micro-environment for germination and seedling development (Lakshmanan et al, 1993:5). Seed coating provides an opportunity to package effective quantities of materials such that they can influence the seed or soil in seed-soil interface (Scott, 1989 cited by Lakshmanan, et al., 1993:5). As bioslurry contains soluble nutrients and numerous active substances like enzymes and vitamins secreted by microbes which are capable of promoting metabolism of the seedlings and because slurry also possesses anti-disease, anti-cold properties (Zhicheng, 1991 cited by Lakshmanan, 1993:50), it holds promise as an effective seed coating medium (Lakshmanan, 1993:5).

Preliminary research in bioslurry use in seed treatment (pelleting, soaking, spraying, dressing, etc.,) as well as control of insects in stored grain have been carried out in the past few years. Shen (1985) reports that spraying digested slurry only or with little pesticide can effectively control red spider and aphids attacking vegetables, wheat, and cotton. The effect of effluent with 1 5-20% pesticide on controlling pest is the same as the pesticides. In this sense there is potential for biogas slurry to reduce cost of production and pollution (Kate, 1991:13). Shen (1988) has also shown that basal dose of barley seeds with anaerobically fermented sludge can very effectively control the barley yellow mosaic virus which is one of the most destructive diseases in barley growing areas of India. It has been estimated that barley yield can be increased by 20-25% by the destruction of 90% of the virus in this way. It is achieved because slurry dressing prohibits large amount of pathogens and eggs from entering into the seed by creating slurry coat around the seed and by producing volatile substances as methane and ethyiene which form a protective layer around the coat. The higher formation (than in the control) of Vitamin B 12 and hormones like auxinns, kinins, and gibberlins in the treated plants also offer resistance to diseases (Kate, 1991:15). Seeds pelleted with 20% digested slurry was reported (Lakshmanan, 1988) to have given higher okra (bhendi) pod production in India. Seed pelleting in blackgram using effluent slurry at 50% w/w is reported to have increased yield by 35% over control (Kate, 1991:15). Preliminary studies carried out at Annamalai University in South India during 1989 indicated the suitability of bio-digested slurry as seed coating medium for rice and pulses (Lakshmanan et al., 1989). Confirmatory trials were conducted during 1989-92 in rice, sorghum, soybean, blakgram, and greengram. Following results were obtained

46

Rice:

Table 55: Effect of seed coating with biogas slurry on rice yield South India Treatment Grain Yield (t ha -1) Straw Yield (t ha-1) Wet slurry Dry slurry Wet slurry Dry slurry Control 4.87 4.22 6.52 5.64 Seed Coating with: Biogas slurry 50% + Azospirillum 1%

A 41

Azospirillum 1% 5.14 4.43 6.87 5.78 Zn SO4 2% 5.51 5.50 7.16 7.04 Biogas slurry 50% + Azospirillum 1 % Biogas slurry 50% +ZnSO4 2% 5.28 5.21 7.16 7.20 Azospirillum 1 % + ZnSO4 2% 5.65 5.77 7.52 7.69 Biogas slurry 50% + ZnSO4 2% 5.74 5.93 7.61 7.45 + Azospirillum 1% Gum Arabic 1% 5.91 6.19 7.49 7.64 0.6! 0.23 0.15 0.18

Source: Lakshmanan, 1993:7

Coating with bio-digested slurry at 50% + azospirillum at 1% + Zn SO4 increased grain yield by 1,04 and 1.97 t ha-' over the uncoated in wet and semi-dry conditions, respectively, inclusion of ZnSO4 in the slurry medium gave more yield than slurry alone. Coating with digested slurry alone gave more yield than the uncoated in both wet and semi-dry conditions. 'Increased yield in slurry coated seeds might be due to the supply of readily available ammoniacal nitrogen and micro nutrients from bio-digested slurry' (Lakshmanan, 1993:7).

Sorghum (Sorghum bicoior):

Table 56 provides data on the effect of seed coating with bioslurry on sorghum yield

Table 56: Seed coating in sorghum Tamil Nadu, India Treatments Grain yield (t ha -1) Seed coated with: Biogas slurry 50% (w/w of seed) 2.36 Biogas slurry 50% + Zn SO4 1% 2.49 Biogas slurry 50% + Azospirillum 2.57 Biogas slurry 50% + ZnSO4 + Azos. 1% 2.66 Uncoated 2.32 Critical Difference (p = 0.05) 0.08

Lakshmanan, 1993:7

Seed coated with bio-digested slurry 50% + Zn SO4 I % + azospirillum 1 % registered the maximum grain yield of 2.66 t ha-1, which was 14.66 and 12.71% higher than that of the uncoated and coated with bioslurry alone, respectively. Inclusion of either azospirillum 1% or ZnSO4 1 % in the coating medium gave similar effect on grain yield. Coating of bio-digested slurry alone did not influence on grain yield.

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Soybean: In soybean, seed coating with bio-digested slurry, superphasphate, rhizobium, and phospobacteria gave the additional grain yield of 0.64, 0.22. and 0.91 t ha-1 in clay loam, sandy clay loam and sandy loam soils, respectively.

Blackgram and green gram: Seed coating with bio-digested slurry and di-ammonium phosphate recorded the additional grain yield of 0.47 and 0.59 t ha'' over the uncoated in blackgram and green gram, respectively. Seed coating with bio-digested slurry, azospirrilum and ZnSO4 increased the grain yield by 1.04 and- 1,97-1 ha ' in rice over the uncoated in wet and dry conditions respectively

Seed soaking with biogas slurry:

Zhicheng (1991:46-48) reports from China that seed soaked slurry improved germination rate, developed into better plants that were greener and less susceptible to disease.

Rice or wheat seeds were packed in plastic-knitted bags. The mouth of the bag was closed by a rope. In addition, the bag was roped in several circles to avoid bursting. The seed bags thus prepared were hanged submerged in the slurry of a running hydraulic anaerobic digester (48 hours for rice seeds and 5 hours for wheat seeds). Seed was soaked in the fresh water with the similar procedure. The results are presented in Table 57 below.

Table 57: Efficiency comparison of seed coating with digester slurry and fresh water (rice) Soaking method Variety Soaking quantity

% Duration for

germination (days) Sprouting rate % Sowing

quantity (kg/mu)

Digested slurry Cuangyoqgsing 5 5 98 0.85Fresh water Guangyoqging 5 8 89 1.00 Source: Zhicheng, I 991:47 1 mu = 0.667 ha

As the above table shows, the time required for sprouting of the seeds soaked in digester slurry was less than that of the seeds soaked in fresh water, the budding rate of the former was 10% higher than that of the fatter. The sprouting rate for digester soaked seed is higher thus the amount of seed required is reduced. In addition, following advantages were observed • Strong and uniform budding • Better development of roots • Seedlings with green leaves and strong stem • Seedlings resistant to diseases and pests as well as cold • Higher survival rate of seedlings (Zhicheng, 1991:46)

Another experiment was conducted in China with slightly different treatments. Table 58 below presents data from this experiment

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Table 58: Comparison of results of different seed soaking methods (wheat) Treatment method Sowing area

(mu) Variety Survival of seedlings Seedling

survial rate (%)

Actual seedlings

Seedling/mu

Seed soaked with Digested slurry Digested slurry + yield increasing bacteria

Fresh water

0.105 0.105 0.105

Nongqi Nongqi Nongqi

1.922 1.620 1.467

18.30 15.40 13.92

99.8 84.1 76.2

Source: Zhicheng, 1991:47 1 mu = 0.667 ha

The fresh water treatment showed the lowest (76.2%) survival rate. Following explanations were provided for this performance of digester soaked seeds:

• In a normally running and functioning digester, the slurry formed is usually rich in soluble nutrients which are demanded by crops for their growth and development.

• There are numerous active substances (enzymes and vitamins secreted by microbes) present in the slurry which promote metabolism and growth of seedlings. In addition disease resistance and cold tolerance is developed and a better foundation for the somatic functioning of genes is established.

• Because of large amounts of ammonium ions in the slurry, pathogen and worm ova are removed from the surface of the seeds. In addition digested slurry in relatively free from pathogens and parasitic ova.

• Soaking in the digester temperature favours the normal physio-biochemical changes in the seed as compared to the ambient temperature outside the digester subjected to the seed in fresh water soaking (Zhicheng, 1991:47-48).

In India, Kanwar et al. (1993:10-1 1) reports the results of a laboratory experiment on the influence of biogas slurry on germination and early seedling growth of bread wheat The experiment involved the following treatments:

• for slurry treatment, seeds were packed in cloth bags and dipped into slurry of a running hydraulic anaerobic cattle dung digester for 6, 9 and 12 hours.

• seeds of bread wheat were soaked in fresh water for 6, 9, 12 hours

• the slurry thus treated were surface washed with running water to remove slurry adherents from the surface of the seed.

The results reported were:

Germination:

• Treatment of seeds with water and slurry resulted in significant increase in germination percentage as compared to untreated seeds. Seeds treated for 6 hours with slurry showed highest germination percentage. Other soaking durations were also at par statistically.

• Slurry removal after 6 hours soaking resulted in reduction in germination percentage.

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• Mean germination time was significantly reduced by water and slurry treatments. Slurry treated for 12 hours was effective In a pronounced way (water treatment for 6 to 9 hours was also equally effective).

• Removal of slurry from seeds resulted in increased mean germination time particularly at 6 and 12 hours duration.

Root Length

• Root length of seedlings raised from slurry treated seeds increased significantly. Slurry treatment resulted in maximum increase in mean value of root length as compared to water treatment.

• Removal of slurry, after 6 and 9 hour of soaking caused reduction in its promotory effect on root length.

• Kanwar et at. (1993:! 0-12) also report about a relatively more sophisticated experiment on the effect of bioslurry as a dressing agent on the performance of rice an maize involving the following treatments.

• For slurry treatment, seeds were packed in cloth bags and dipped in an anaerobic digester (fixed type biogas plant) operating on cattle dung (for 12, 24 and 48 hours).

• Seeds of maize and rice were soaked in the fresh water for 12, 24, 48 hours.

• The slurry -treated seeds were surface washed with running water to remove any surface adherents of slurry from the seeds.

Results

Germination

• All the treatments increased germination except untreated controls.

• Biogas slurry was less effective and rather its removal from seed surface resulted in slight increase in germination.

• Twelve hours time was better than other soaking duration.

Mean Gemination Time (MGT)

• MGT is reduced by 12 and 48 hours soaking duration in maize and 48 hours in rice.

• Removal of slurry from surface of seeds did not yield any significant effect on MGT.

Mean Root Length (MRL)

• Slurry treatment of 48 hours resulted in significant increase in MRL (Maize).

• In rice, slurry treatment proved to be less effective than other treatments as long as MRL is concerned.

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Mean Shoot Length (MSL)

• MSL increased significantly in all the treatments (maize)

• No significant increase in MSL in slurry treatment (maize)

• Removal of slurry did result in slight increase in MLS (maize)

• In rice air the treatments increased MSL but the MSL increase in slurry treated seed did not override the influence of other treatments

Mean seedling length of pot grown plants

• Treated seeds grown in soil showed better growth of seedlings in comparison to control.

• However slurry and water treated seeds did not differ in mean seedling length.

• The removal of slurry from seeds did not effect seed performance.

On the whole, it was found that the application of slurry significantly improved the seed performance over untreated seeds but its effect was equal or less pronounced than water treatment. When slurry was rinsed-off before germination its germination value increased. This finding contradicts the earlier finding of Zhicheng (1991) in China in which digested slurry treated rice and wheat seeds showed pronounced effects over seeds soaked in fresh water. Kanwar et al. have observed that removal of slurry from seed surface caused improvement in seed performance in relation to some parameters which indicated "slurry application for longer duration and its persistence on seed may prove to be futile or less effective for seed growth' (Kanwar et al., 1993:12). However, it is also plausible that the Chinese experiment (Zhicheng, 1991) did not involve surface washing with running water to remove surface adherents of slurry from seeds and it might well be the reason behind the better performance of slurry treated seeds as compared to seeds treated with freshwater. Anyway, Zhicheng's (1991) findings could not be confirmed. Of course, Kanwar's (1991, 1993) experiments included design to incorporate these concerns. The findings are far from being conclusive.

Use of biogas slurry on the prevention and cure of crop diseases:

Very few research works have been carried out in use of biogas slurry in desease/ pest control. Some of the preliminary results are reviewed below.

Control of rice diseases and pests An experiment was conducted in 1988 in Hunan Province of China to see the possible effects of biogas slurry in controlling some of the rice diseases and insect pests (Jiasi et al., 1991:49-52). The effect of fertilising with slurry and urea was compared to fertilising with human faecal matter and ammonium carbonate and urea fertilization. Slurry fertilizing proved superior, in some cases, far superior, in reducing disease ( mildew, helminthosporium, sigmoideum) and in restricting attacks by insects (leaf weevil, rice weevil). The yield was also higher than that given by the control.

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Wheat gibberella disease

An experiment was conducted in the Shanxi province of China where (Zhengshan, 1992:24-27) wheat gibberella disease used to occur, sometimes seriously. Biogas slurry was taken from the outlet of the normal biogas digester treating human and animal wastes. Two control tests were carried out, one using clear water and one using a pesticide. The results of the slurry test corresponded approximately to those of the pesticide test. More specifically, the incidence of wheat gibberella disease was reportedly 20% lower than the contrast; relative effect of prevention and cure increased by 45% which was similar to Bavistin. It was also concluded that best effects could be obtained by spraying undiluted biogas slurry @ 50 kg/mu (75Ot/ha). in this way both pesticides cost could be served and pollution caused by these pesticides be reduced.

Control of storage insects

Use of chemical fumigants to control storage insects and pests have their own sets of disadvantages. Residual effects, handling hazards, resistancy development etc., are the disadvantages that are often cited. Even the practicality of CO2 as a fumigant is hampered by the availability of containers and other requirements at farmer's level.

Effectiveness of biogas as a fumigant for control of pests during storage of paddy has been demonstrated under laboratory conditions (Biogas Forum, 1994:15-16). In India, study was conducted by Mohan et at. {1992:229-232, excerpted in Biogas Forum. 1994) on the use of biogas from cow-dung for insect control during storage.

A leak-proof bin of 100 kg capacity was developed for biogas fumigation. The bin was made of a special type of PVC. It was rectangular in shape with a circular top position closed with a removable air-tight lid. The biogas inlet gate valve was fitted at three quarters height of the bin so that the space below the Inlet value could be filled with pigeon pea seeds and the remaining space at the top would be occupied by biogas. An outlet was provided in the lid to facilitate checking for the presence of biogas.

The testing was carried out on 100 kgs of grains placed in the bin and supplied with biogas at 1.4 kg/cm2 pressure

Result:

• It was found that there was significant difference in insect mortality between 3, 5, 7, 10 and 12 days of fumigation at different layers of stored grain.

• One hundred percent mortality of eggs, grubs and adults was found on the 10th and 12 th days of fumigation.

• For adequate penetration of the biogas at different layers a pressure of 1.4 kg/cm2 should be applied for a minimum of 10 days.

• An analysis of treated grains showed no significant amount of CH+ residues.

It was concluded that these findings hold great significance for the future of agricultural produce storage. However, more research is needed in this area. As the editor of Biogas Forum (1994:15-16) rightly comments, it will be difficult for a farmer to create a pressure of 1.4 kg/cm2. Further research into the possibilities of prolonging the fumigation period with lower pressure is perhaps the needed research agenda at this stage.

52

Foliar dressing with effluent slurry:

In China, foliar dressing with effluent slurry gave better crop yields than dressings done with chemical fertiliser alone {Shen, 1985). Foliar dressing provides both nutrition as well as moisture. Perhaps these may be the reasons for improved yield performance.

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Chapter 4

Sanitation and Public Health Aspects of Slurry Utilization in Crop production

4.1. Preliminaries

Environmental benefits of biogas technology in terms of reduction of fuel-wood dependency and soil erosion, etc., have been discussed and reviewed in numerous publications. The same is the case with environmental consequences of chemical farming in general and excessive chemical fertilizer use in general (e.g. Shiva, 1988). The betterment of household sanitation, in terms of human and animal waste disposal and smokeless kitchen and its positive effects on health, has been frequently written about and commented upon in the context of biogas technology, in addition, the practice of utilizing organic manure including manures from biogas plants (as the earlier chapters showed) are frequently taken as ' environment friendly', ' natural7 and as a part of ecological agriculture that presumably has better sustainability as compared to chemical agriculture which is largely dependent upon non-renewable energy resources. This review will not delve into these areas because an extensive attempt to review will have to include. The existing general, interrelated literature ranging from the romantics (e.g, Walt Whitman1 and latter, Walden Berry (1976,1977), to empirico-romantics (e.g., Fukuoka of the One Straw Revolution fame) to environmentalists of anti - modernist pursuits and even post -modernists. The literature in this sense is already too much voluminous.

In addition, the following review will also deliberately exclude public health and sanitation aspects of the contamination of biogas slurry with toxic organic compounds (e.g. halogenated organic compounds and polycondensed aromatic compounds), heavy metals, and radioactive substances. These contaminations at present cannot be a source of major concern to small operators in developing countries like Nepal because of the nature of the feedstocks used (generally livestock and agricultural waste matter). The highest risk of heavy metal contamination of bioslurry exists for those plants that process waste water x a substrate proceeding from certain industrial plants (e.g., metalworking, electro-chemical industry, paints and dyes) (Kone, 1991:10). Plants designed for the treatment of the municipal sewage can be exposed to critical concentration of heavy metals, which prohibit the utilization of bioslurry as manure on cultivated farmland (bid). The immediate concern in Nepal and many developing countries are related to the sanitation and public health aspects of biogas slurry derived predominantly from animal, human and agricultural wastes.

it is obvious that that most epidemic diseases in the rural areas of the third world countries result from dirty water and poor management and disposal of excreta. The latter is even more important since poor disposal of excreta may cause the pollution of water source and the breeding flies which are media for the spread of diseases. If the untreated excreta are directly used 2s fertiliser, pathogens in them easily spread (APRBRTC, 1983:161).

4.2. Excreta born diseases and organisms

Numerous viruses, bacteria, nematodes and fungi are present in human and animal excreta. As will be seen the number organisms reported are more in human than in animal excreta. Table 59 below presents a compilation of types of organisms and the diseases associated with them.

1 This American icon has even a poem called 'This Compost1 besides 'The Leaves of Grass' to his credit-Readers with poetic inclinations can refer to the Complete Biogas Handbook (d-House,1978:322')

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Table 59: Excreta-borne organisms and diseases2 Common Name Scientific Name Disease

Helmimhiasis Schistosoma

S. mansoni, S. japonicum S. haemaiobium

Scnistosomiasis (Biha roasts}

Hookworm Round worm

Nectar americanus Ascaris lumbricoides

Hook worm diseases Ascariasis

Tapeworm Thread worm

Taenia saginata Taenia solium Stroglyloides stercoralis

Tape worm infestation (Teeniasis) Thread worm infestation

Pin worm Whip worm

Enterobius vermiculoris Trichuris trichuria

Enterobiosis Tnchuriasis

Selmonete ryphi Typhoid Citrobacter Camoybacte

Salmonella paratyphi A,B. or C Staphylococcus aureus Pseudomonas aeroginosa Escherichia coli Proteus vulgaris Vibrio cholerae

Para typoid Pneumonia, boils, internal absecces Urinary tract infections Normally harmless but can cause gastro-intestinal infection Urinary tract infection Cholera Infection of the urinary tract, gall bladder, etc Dirrhoea

Shigella spp S. dysenteriae

Shigellosis Bacillory dysentery

Hepatitis A,B,CD Polio virus Epstein Barr-virus Echoviruses Coxsackie viruses Reoviruses Advenoviruses Echoviruses Rotaviruses

Entamoeba histolytica Giardia lamblia Balantidium coil

Viral Infectious hepatitis Poliomyelities Protozoal Amoebic dysentery (Amoebiosis), ulcer of colon, liver absecces Diarrhoea and malaosorption Mild diarrhoea, colonic ulcer

Source: APRBRTC, 1983:162; Martin, 1994; Satyanarayana et al. 1986; Navrekar, 1986:53; Mapuskar, 1986:59-63, Khandelwal, 1986:108 2 This listing is not based on the analysis of a single human excreta sample. The organisms are reported by different authors. The list does not include organisms specifically reported for cattle or buffalo dung. These will be provided in a separate table.

55

Table 60 was presented to show how potentially danger human excreta is if it is not disposed safely. It is obvious that these parasites/ pathogenic organisms may not be present in one sample at a time at a place.

Biogas plants are obviously important for health and sanitation from the point of view of organised disposal of animal and human wastes. They are even more important in situations where toilets are not constructed and defecation in the open spaces are accepted norms as in many parts of South Asia. A quote from India is pertinent here

".... our people are yet to accept the use of biogas plants with latrines connected. As per Manusmriti, it is stated that latrine should be located 400 steps away as defecation is considered dirty. In the conventional communities orthodox people visit latrines by putting on separate clothing. The Mohejodaro excavations have revealed the provisions of bathroom and drainage but not of latrines, implying thereby the prevalence of open defecation which corroborates belief in Manusmriti" (Patel, 1986:26)

In India it has been reported that human wastes are responsible for 80 percent of the diseases (Dayal, 1986:3). Even if this single source is responsible for half of this percentage of diseases, that is a matter of grave concern, in India, below I percent of the rural population reportedly enjoy sanitary facilities and 33 percent of the urban population have no toilet facilities (ibid). It has also been reported that only 20 percent of the household are covered by sewerage. Only 14 percent of urban households use latrines that are connected to septic tanks (Dhussa and Myles 1986:86). The situation in the rural areas must be worst. The number of those resorting to defecating in open spaces is thus enormous. It has been estimated that the resultant cost in terms of medical treatment and lost production is around Indian Rupees 4.5 billion per annum (Dayal 1986:3). Statistics are not available, but no one is in the position to say that the situation is better - off in Nepal.

Similarly, it is not unusual to find human and animals living almost together in smaller farming households. Spreading of pathogens to humans under these circumstance is easily understandable. Adoption of biogas technology not only leads to the formation of a sort of 1 clearing house' for these waste materials subsequently leading to better sanitation and public health, it also reduces the potentials and number of pathogens substantially so that when the digested output is used in agriculture, sanitation conditions are improved and health risks reduced as compared to the practices of utilising undigested animal and human excrete (or leaving them scattered throughout the courtyards or open spaces near the homesteads).

The concern of this chapter is the health and sanitation aspect of biogas slurry (produced out of both human and animal excreta) when it is used as fertiliser for crops.

The purpose in this review is to examine the extent of removal of these different parasites and pathogens during anaerobic digestion.

4.3. Research in pathogen/parasite survivability

Shanta (1970 cited in Satyanarayana et al., 1086:14-15 ) carried out laboratory studies to determine helminth parasites removal during night soil digestion at 37°c. Table 60 presents the results

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Table 60 : Percent reduction of helminth ova in laboratory night soil digester

Loading Detention pH Influent Effluent % Reduction

rate time (days) No. Ova/ Litre No. Ova/Litre Kg./VS

Ascaris Hook Ascaris Hook Ascaris Hook worm worm worm

2.21 20 7.50 4000 58200 2080 21360 48.0 63.2 1.78 25 7.60 114000 18200 38324 1639 66.5 90.6 1.45 30 7.65 94110 21820 28248 1528 70.0 93.0

Source;-Satyaiwayana-et.al.,.1.98-6:15

The table shows that ascaris eggs survive for longer period than hookworm. In the case of hookworm, 90% of ova is reduced as compared to 70% reduction in ascaris ova in a 30 days detention period. These parasite ova are removed to the extent of 67% and 91% respectively at a detention period of 25 days. It has also been observed that the sludge and supernatant still contain viable eggs. Prolonged use of thermophilic digestion process may result in lysis of the micro-organisms and also results in the destruction of pathogenic bacteria as well a parasitic ova in the night soil (Henze et al. (ed.) cited in Satyanarayana et al., (1986:9).

From public health and sanitation aspects, Kshirsagar (1986:37-43) presents a profoundly cautious interpretation of the available information on biogas slurry produced from human excreta. He gives the warning that "night soil-based biogas plants which are being propagated as a health protection and energy conservation measure may themselves turn out to be the source of dissemination of diseases unless utmost care is taken at all stages". He further warns that "if the nightsoil is to be manually collected from elsewhere for feeding into the digester the scavengers come into direct contact with pathogens. It is possible for the pathogens to survive in large numbers in the digester and pass over to the effluent. Anaerobic digestion over merely 30-50 day's detention time is unhelpful for pathogen destruction. Even the drying of effluents removed after this insufficient detention time does not help in making the manure innocuous. There are great hazards if the crops grown with such manure are eaten raw. The use of sludge on crop lands or in fish farms suffer from higher incidence of infections of helminthic and intestinal pathogens, the workers on sludge- fed forms, too, are likely to be victims;/(ibid).

Kshirsagar (1986:38) justifies his argument of the persistence of pathogenic organisms in the digested effluent as follows:

".... conditions in biogas units are much the same as are prevalent in the biogas of living human beings. These conditions are taken advantage of by the pathogenic organisms discharged by sick persons or by the vectors which are thus potentially present in the feed to digesters. Obviously these pathogens will survive in the digestion processes in large numbers. Some reduction would, of course, occur due to attack from predators. Thus, the process of anaerobic decomposition even if carried out in a controlled manner is not helpful in destroying pathogenic organisms within the detention period of 30-35 days normally deployed. Hence the effluent slurries coming out of the nightsoil fed biogas units will be equally hazardous to handle, dispose of or utilise in the field as manure."

57

Kshirsagar argues that some of the pathogenic organisms (e.g. those of amoebic dysentery) which can form cysts or the eggs of some of the helminths will remain "totally unaffected" while passing through the anaerobic digester. For agricultural use sun -drying (for 10-20 days) is recommended. Even with this some of the pathogens survive. He suggests that farmers working even with dried slurries (cakes) should be advised to use protective gears.

According to Chanakya (1986:45) the optimum time of 35-52 days used in the conventional dung based plants will not hold good for digesters designed to be run on night soil because during this retention period many pathogens present in night soil will still be viable and it would be dangerous to discharge such effluents.-into the open permitting human handling and exposure to vectors of decease transmission. The design of the plants needs to be modified so that pathogens are retained (or inactivated) within the digester while only the excess water and spent solids are discharged for secondary treatment. According to Navrekar (1986:52-56) if the actual retention time is low, the effluent from aquaprivies and septic tanks and even from conventional sewerage treatment plants contain a high percentage of viable pathogens. Only the biogas plant system has the potential system; in that too, only the fixed fixed-dome system with a composting complement, is considered ideal.

The ova of helminths are reported to be denser than the night soil slurry. During liquefaction phase the ova settle down at the bottom. Within 20 hours, 95% of the ova get settled. The hookworm ova survive only for nine days under anaerobic conditions and those of schistosoms and ascaris can survive up to 10 days. If the ova get separated perfectly they can be retained at the sedimentation space below the outlet pipe. The ova can be retained at this space for more than 100 days causing their deactivation. Similarly, bacteria like Salmonella spp, Shigella spp, Vibrio cholerae, Mycobacterium tuberculosis, that are commonly spread through faeces, cannot survive when subjected to anaerobic condition at 22 - 37° for about 20 days (range: 6 to 20 days) (Navrekar, 1986:56).

When the effluent/sludge come from biogas plants, the remaining chances of pathogen survival is completely reduced. The temperature of 50° to 60° C, generated in a properly managed compost, kills the pathogenic flora within a short period of time.

Tables 61 .a. below presents data on the survivability of a number of organisms during anaerobic digestion and in the sludge.

Table 61. a.: Survival time of pathogens in some excreta disposal system Organisms Pit and composting latrines

with 3 months retention Anaerobic digestion at 32°O 35°C

Survival time in sludge

Enteroviruses Less than 3 months 28 days 3 months Bacteria Salmonella typhii Salmonella paratyphii Shigella Vibrio choierae Pathogenic E. Coli

-do- -do- -do- -do- -do-

4-5 weeks 4-6 weeks 9-10 days 7-14 days 4-8 days

1 month 1 month 1 month 5 days 5 days

Protozoa Entamoeba histolytica Giardia lamblia Balantidium Coli

-do- -do- -do-

3 weeks -do- -do-

2 weeks -do- -do-

Helmiths Ascaris lumbricoides Ova survive Ova survive Ova survive Enterobious -do- -do- -do-

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Vermicularis Ankylostoma dudenale •do- -do- -do- Strongyloides •do- -do- -do- Sterooralis Taenia saginata -do- -do- -do- Taenia solium -do- -do- -do- Trichuris trichiura -do- -do -do Source: Mapuskar, 1986:63

The table shows that with a digestion temperature of 32-35 degree centigrade most organisms are eliminated but the helminth ova survive in this temperature and retention time. This has consequences for the adjustment of the retention period as well as temperature to be maintained within the digester. Perhaps the design aspect is linked with these adjustments.

Table 61 .b. below provides a detailed picture of the relationship between temperature, retention time and the magnitude of pathogen/parasite elimination.

Table 61 .b.: Temperature, residence time and die-off rate of parasites and pathogens Organism Category Temperature °C Residence time Die-off (%) (Days) Poliovirus Viral 35.2 2 98.5 Salmonella spp Bacterial 22-37 6.20 82.96 Salmonella typhosa -do- 22-37.6 6 99 Mycobacterium tuberculosis -do- 30 Not reported 100 Ascaris Parasite Helminthic 29 5 90 Cysts -do- 30 10 100

Source: Gupta, 1986: 69

The table is self-explanatory. With a digester temperature of 37.65 degree centigrade and a retention period of ten days organisms listed in the table are eliminated.

If these are based an accurate analysis, adoption of biogas plants and the prospects for the use of slurry for crop production is bright from public health and sanitation aspect. Composting of slurry/sludge is claimed to further reduces any chance of the pathogen spreading to the environment. Table 62 below presents a comparison of pathogen survived in an unheated anaerobic digestion and composting.

Table 62: Comparison of pathogen survival in unheated digestion and composting Organism ln-unheated anaerobic digestion In composting 1. Enteric May survive for over three months Killed rapidly at 60°C 2. Salmonellae May survive for several weeks Killed in 20 hrs at 60°C 3. Shigellae Unlikely to survive for more than a few

days Killed in hr. At 55°c or in 10 dys at 4O°c

4. E-coli May survive for several weeks Killed rapidly killed above 60°C 5. Cholera May survive for one or two weeks Killed rapidly 55°C 6. Lepotospire Survive for not more than two dys Killed in 10mts.AtS0°C 7. Entamoabacysts May survive for three weeks Killed in 5 mts at 50°C and 1 day at

40°C8. Hookworm ova Ova will survive Killed in 5 mts at 50°C in 20 hrs. At 50°c and 200 hrs 45°C

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9. Ascaris ova Ova will survive for many moths Killed in 2 hrs. At 55°C in 20 hrs. At

50°C and 200 hrs 45°C 10. Schistosome Ova may survive for many months Killed in 1 hr 50°C 11. Taenia ova Ova will survive for a few months. Killed in 10 mts. At S8°C and in over 4

hrs at 45°C Source: Navrekar, 1986:57 mts-minutes; hr-hour

The reports are contradictory at times. The retention time-temperature is a matter of lively debates and controversies in India.

Singh (1986:65-66) reports that poliovirus 35° C is reduced by 98.5 percent within two days. Within the temperature range of 22°-37°C, Salmonella lyphosa is reduced by 99 percent in 6 days. Salmonella spp is reduced by 82-86 percent in 6-20 days. Mycobacterium tuberculosis is killed 100 percent at 30°C. All encysted helminths are destroyed except ascaris cysts which are able to survive even after 14 days at 35°C. Ascaris cysts are completely digested during thermophilic digestion (48-60°C). if digested slurry is dried and stored for about six months the ascaris cysts are destroyed even if the digestion was achieved in mesophilic (below 40°C) temperature. Singh concludes that anaerobic digestion of human excreta removes most pathogens and improves public health and sanitation. With the storage of effluent in solid system, it can be used as manure with reduced health hazards. Such a conclusion is also reached by Gupta (1986:69). He, however, notes that effective destruction of pathogenic enteric microorganisms does not preclude the survival of at least some micro-organisms of public health significance. But these organisms continue to die-off because of the lack of nutrients and the hostile environment during storage, drying and application to the soil. Contamination of crops by surviving pathogens is achieved by pasteurization in European countries (ibid). However, in the Nepali and South Asian context as a whole, such a process is economically not feasible. Khandelwal (1986: 105-109) is similarly optimistic about the potential of biogas plants to eliminate pathogens. According to him pathogenic bacteria get killed if the actual retention time in the digester is 14 days at 35°C. The die-off rate of enteric viruses reported is 22 percent at this level of temperature and retention time. In line with the analyses and arguments put forward by Navrekar, Singh, and Gupta, Khandelwal asserts that "there is no cost effective method which can match anaerobic digestion in the destruction of disease producing organisms. Composting can kill the most of the remaining pathogens" (Khandelwal, 1986:105). According to Khandelwal, use of spent slurry not only improves soil fertility leading to increased agricultural production, it is also an operation of waste disposal leading to better sanitation.

Khandewal reports that plate counts of spent slurry for micro-organism of the farm manures and human excreta samples showed the presence of highest number of bacteria (38 nightsoil.

Table 63 below presents a list of species of bacteria, fungi and other organisms in a sample of farm manure and predigested night soil from India.

Table 63: Organisms isolated from farm manures and non-digested nightsoil Group

Sample Bacteria Fungi Others Night Soil Escherichia coli Rizopus Ascaris Proteus vulgaris Penicillium lumbricoides (eggs) Citrobaaer Aerobacter aerogines Aspergillus

Staphylococcus aureus

Salmonella paratyphi Pseudomonas aeroginosa

107) in

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Farm manures (poultry and cattle dung)

Escherichia coli Citrobacter Aerobaaer aerogenes Pseudomonas Bacillus

Rhizopus Peniciilium Aspergillus Mucor Pilobolus

Actinomycetes

Source: Gaur et al., 1986:108

Some of these organisms are pathogenic while others are non-pathogenic normal commensals of the gastro-intestinal tracts. However as shown earlier (Table 59), the list of pathogenic organisms in human faeces reported by researchers is long. Even if the case with animal manures is the same the number of pathogens reported are relatively low.

The review reveals that even in a country like India where biogas has received such an enormous interest both at the policy levels and research institutions, there are still many unsettled issues pertaining to health and sanitation aspects of slurry utilisation in agriculture. However, firstly, the major issues on which consensus seemed to have reached among the scientists are as follows.

• On-site disposal systems for human waste through anaerobic digestion are best suited for India. Anaerobic digestion in a biogas plant is hygienically a very promising and desirable system

• Plants designed for human waste should give primacy to hygienic considerations.

• Raw human wastes should not be manually handled

• Undigested or semi-digested nightsoil should not be exposed to surroundings. Care must be taken to see that insects or animals do not get access to it.

• Pathogen survival time in the effluent slurry should be the primary concern in the design of biogas plants. Only these designs which fulfill health parameters (i.e. maximum pathogen elimination) should be permitted for wider adoption.

• The benefit cost ratio of nightsoil biogas plant operations should be increased by gas production efficiency and by optimizing manurial value. This should be done by considering public health aspects as the first requirement of a nightsoil biogas plant.

• In terms of quantity, human waste is an important resource of plant nutrients, next only to animal waste.

• Spent slurry is rich in nitrogen but drying is considered not a desirable method

• The idea of enriching slurry with rock phosphate, superphosphate and preparation of

• organo-mineral biofertilizer should be systematically explored.

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• Preliminary tests show that the addition of 15% ammonia solution to the spent slurry kills

pathogens. This needs to be systematically explored. • Further studies on survival of pathogens in the digester as well as during application of spent

slurry in agricuiturai fields and fish pounds need serious considerations due to the importance of the manurial aspects of slurry in the total biogas system.

• Suitable mechanical devices should be developed for handling the effluent • Field trials need to be conducted on the use of different forms of slurry from different

feedstocks for manuring in agricultural fields and fish ponds. • Spent slurry from excreta fed plants can be used for manuring crops after adequate dilution.

It can be used for composting other organic wastes. • Effect of spent slurry from excreta fed plants on physical, micro-biological properties of

soils including health and sanitation, socio-economic benefits and costs need to be studied further.

• Adoption of a multi-disciplinary approach {health, sanitation, agriculture, forestry, fisheries etc.) has to be evolved to facilitate a package approach in slurry utilisation.

• Mass awareness on the various aspects of the excreta fed biogas should be created.

• Major disagreements

Those who support nightsoil based biogas plants keep on arguing that whatever the imperfections and the resulting hazards, the situation will be better than open defecation. Others claim that human faeces based effluent slurries are not quite free from pathogens, and that by virtue of its fluidity spread the contamination to the wider environment. Researches belonging to this camp also agree that nightsoil's biogas potential, however great per unit of excreta, is negligible in the total because the per head output of human faeces is only one twentieth (or even less) of the cattle's per head output of dung. This potential is considered to be insignificant in comparison with the total nutrient potential of biogas from cattle and plant wastes. This ' little amount of methane' is considered not worth the risks of faecal effluent slurry, which could pollute a greater mass than the solid excreta ever could. It has been agreed that sanitary disposal of excreta can be achieved by other means such as anaerobic composting of four to six months' duration or aerobic composting of four to five week's duration. Because composting is recycling as far as nightsoil is concerned "let us not aspire for gas from night soil because the faecal slurry produced in the process is far from safe" (cited by Ghosh, 1986:135).

Disagreements on specific scientific and technical Issues:

Hydraulic Retention Time (HRT), temperature and pathogen survivability:

Wider differences in opinion with regard to the HRT is evident among the scientists involved. HRT is linked to the survivability of pathogens which in turn, has consequences for the utilization of slurry as manure.

Satyanarayan et al. (1986:23-25) claim that "at an average digester temperature of 28°C, some 67% ascaris and 90% of hookworm eggs were destroyed during a retention period of 25 days." Parikh (1986:74-77) on the other hand claims that ascaris eggs "neither grow nor die at 27°C for 40 days", and that parasite eggs can survive for 15-40 days at 2O-3O°C temperature." Gaur and Khandelwal (1986:105-109) claim that pathogenic enteric bacteria are killed if their actual retention time in the digester is 14 days at 35°C. The die-off rate of even the enteric viruses is reported to be 22% at this level of temperature and retention time. Chanakya (1986: 100-102), on the other hand, reports that

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enteric viruses can persist for 180 days at 2O-3O°C and considers that retention time of 35-52 days insufficient for night soil digesters. Gupta (1986:68-70) claims that a retention time not shorter than 14 days at a temperature not significantly lower than 30C, to be sufficient reasons that at this level of operation, pathogenic enteric micro-organisms, with a few exceptions, are effectively killed. He argues that since pathogens, in any case, cannot be destroyed hundred percent and that effluent should be and can be effectively utilised because most pathogens are destroyed during digestion and remaining few continue to die off due to the hostile environment in which these organisms cannot receive appropriate nutrients!

Such a lower retention time is opposed by Dhussa and Myles (1986:86-89) who claim that night soil must remain in the plant for at least 70 days to become free from pathogens and parasitic ova. Since public health is of overriding concern, and since it is difficult to exercise control over millions of individual households' practices of composting etc., it is better to exercise utmost control in the digester design itself, most importantly, by fixing the HRT on the basis of winter temperature. In this context the digester's volumetric capacity should also be increased (Ghosh, 1986:139). Mapuskar (1986) however does not favour this approach because the costs involved will be a deterrent for biogas adoption. According to him a retention period of 40-45 days at 32-35°C eliminates the viral, bacterial and protozoa! pathogens; the helminth ova settle at the bottom of the digester. Mapuskar claims that ascaris ova survive in the slurry after 30 days of anaerobic digestion at 32-35°C and even thereafter in the sludge (in contrast to Gupta's (1986) claim that a 90% die-off of heiminthic ascaris within 15 days at 30°C). Even then there is no reason to extend the retention period beyond 40-45 days. It could even be reduced to 25-30 days if retention of effluent for 25-30 days in an adjacent pit for secondary treatment is assured (Mapuskar, 1986: 81-85).

On the application of slurry:

Gaur and Khandelwai (1986:105-109) seem to have no objection on the direct application of slurry (without drying) provided that the land is ploughed immediately after slurry application. In this process ammoniacal nitrogen is saved for use by plants. In addition, plants receive moisture from the slurry. Gaur and Khandelwai also argue (mentioned earlier) that slurry can be mixed with either solid crop residues, farm and city organic wastes, or mixed with already humified compost for maturity before transfer to fields. They also report that slurry can also be composted with phosphatic fertilisers to reduce the loss of ammoniacal nitrogen.

However the uses of fresh slurry out of excreta fed biogas plants is fraught with technical controversies. Gaur and Khandeiwa! was (like Mapuskar) seem to think that the unfavourable environment as well as soil microbes would kill the remaining pathogens in the spent slurry. Kshirsagar's (1986: 37-43) position in this issue was reviewed in detail earlier. He is extremely cautious about the use of fresh slurry from human excreta fed biogas plants as manure. According to him "if labourers working on sewage farms are having a high incidence of infections from helminthic and intestinal pathogens, the workers who would be working with effluent slurries, too, would certainly be vulnerable. Lack of data in this respect cannot be construed as a positive indication of safety in handling and using this material (i.e. sewerage and nightsoil sludge for fertilising land and fish farms)" (p. 39). Kshirsagar thus argues for sun-drying or aerobic composting of effluent slurry. It has also been reported that enteroviruses can come out prematurely and can cause epidemic, and also that pathogens from raw nightsoil can penetrate the cell wall barriers of plant root systems and get into human found sources. Logically, then, for him, it seems plausible that if pathogens from raw nightsoils can penetrate the plant cell and enter human food sources, pathogen remaining in spent slurry may also be able to do the same (Ghosh, 1986:141).

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Thus it seems that convincing data to those differences are lacking, it should also be noted that engineering aspects of biogas plants have been receiving better attention than the microbiological aspects in India. Ghosh has gone to the extent to state that "perhaps it is not microbiology alone, questions of science in general have been side stepped (Ghosh, 1986:141).

The process of elimination of pathogenic ova:

The Chinese rely on the sedimentation procedure to eliminate the ova of some of the important pathogens present in manures and faeces (APRBRXC, 1986).

According to the Chinese reports, the specific gravity of the effluent in the digester is generally 1.005-1.010 as compared to 1.055-1.060, 1.140 and 1.200 of hookworm, ascaris and schistosome ova respectively. As the specific gravities of the ova of these common parasites are heavier than that of the effluent in the digester, these ova sink spontaneously due to their own weight, to the bottom of the digester. Table 64 below presents the settling down time of some of the common ova in a 1 meter deep liquid manure. Table 64: Settling time of some of the common pathogenic ova Pathogenic Ova Setting time (hours) Schistosome (mostly) Ascaris (mostly) Hookworm (45.77%) Ova of all three (96.6%)

2 8 4

20Source: APRBRTG 1986:165

Some ova remain floated in the upper layer. Very few remain suspended in the middle layer. On the whole 95% of the total ova can be found in the sedimented residue. The middle layer is used as fertilizer. All the faecal sediments are left in the digester. Thus, one can see that the number of ova in the effluent is reduced by 95% in comparison with the excreta in the inlet pipe. Ova left in the residue is killed by disinfection and this residue then is also used as fertiliser. Thus, in terms of design, the digester with middle layer outlet is better than one with discharge chamber.

Pathogen survivability, HR.T and temperature: Table 65 below presents summaries of experiments carried out in these aspects in China. The experiments involved putting live schistosome ova in a nylon net bag and placing the bag into a fermenting task.

Table 65: Survival periods of schistosome ova

Ova survival period in the digester (days)

Season

7- I 4 days 15-22 days 26-40 days

Summer Autumn Winter

Source: APRBRTC, 1986:169

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Table 66: Fatality rates of hookworm ova Retention period (days) Fatality rate {%)

6 30 60 90

40 90 99

100

Source: APRBRTC, 1986:169

Table 67: Fatality rates of ascaris ova (summer and autumn) Retention period (days) Fatality rate (%)

18-1 7 100

12.5-44 30

Source: APRBRTC, 1986:169

From another experiment in China (APRBRTC, 1986:169) (using fermenting bottle under anaerobic condition), it is reported that Shigella flexner lasted 30 days at 25°C and 100 days under aerobic conditions (control). Both Salmonella typhi and Salmonella paratyphi lasted about 44 days under anaerobic conditions and 98 days in the cooled boiled water (control).

From these studies it has been concluded that the treatment of excreta in the digester at the ambient temperature is feasible in vast rural areas of China.

Chinese research works find that the optimum temperature range for the survival and growth of ova range from 22-40°C.

Table 68 below presents data on the relationship between temperature and survivability of pathogen ova as reported from researchers in China.

Table 68: Pathogen survivability under different temperatures

Organism Temperature Survivability Ascaris ova 50°C Can live for 20 minutes Ascaris ova 55°C Can live for 10 minutes Ascaris ova 60°C Killed right away Hookworm ova 15°C Can live for few hours Hookworm ova S5°C Killed immediately 5crtistosome ova 45.5°C Can live for 2 hours Schistosome ova 53°C Death occurs within one minute Liplospira 50°C Destroyed within 10 minutes Salmonella 55°C Killed within one hour Salmonella 60°C Killed within i 5-20 minutes Escherichia coli 55°C Killed within one hour Escherichia coli 60°C Killed within 15-20 minutes Source: Adopted from APRBRTC, 1986: 169-170 Studies by Garde et al. (1987:4-8) have shown that mesophilic anaerobic digestion results in complete inactivation of Salmonella typhimurium in 10 days. It is also suggested that since in the Indian design of biogas plants animal dung is digested along with nightsoil with a detention time of more than 30 days, there is no possibility that Salmoneila typhimurium will survive in the digested slurry. Even Enterobacteriaceae elimination under mesophilic anaerobic digestion is seen as a possibility.

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It has also been reported that most viruses except hepatitis viruses may lose their activity at 60°C within one hour.

From thermophilic3 and mesophilic4 experiments conducted in Shangdon Province in China, it is reported that 98% of the ascaris ova died in one day, and 100% in two days. Schistosome, hookworm, saimoneiia and shigelia ova were destroyed within 21 hours. In a smaller experimental digester, Salmonella and shigella were reportedly killed within one day. Also 99.5% of ascaris ova were killed in one day and 100% died after two days under 51°C+_1°G When the temperature was decreased to 48°C+J°C, shigella ova died within one day. Salmonella ova died within 3 days.

From the mesophilic experiments, it is reported that hookworm ova died in 10 days and 96.5%, 98.8% and 99.1 % of ascaris ova died in 20,26 and 33 days respectively.

From Europe Scheffer et al. report that they found no confirmation of the claim that pathogenic typhus- enteritis bacteria are destroyed during fermentation at 30°C. They however believe that anaerobic digestion may be considered a more hygienic process than aerobic systems of manure processing. But the 30°C fermentation temperature requires a very long retention time to yield reasonably safer outputs (cited by Van Brakel, 1980:106)

Thus it is clear that higher fermenting temperature can accelerate the fatality of ova and pathogen. The alternative for lower temperature is longer HRT. In addition it is doubtful whether the Third World small farmers can afford extra energy sources to heat the digester.

Feedstock combinations and survival time of schistosoma:

An experiment was conducted in China in which the feedstock used comprised of 5% human excreta, 90% animal excreta and 5% stalks. The data on survival time of schistosoma is presented below.

Table 69: Relation between feedstock concentration and the survival time of schistosoma ova

Experiment 1 Season Summer AutumnDigester temp. 19-23.5°C 24-24.5°C Outcome Survival days Free ammonia(%) Survival days Free ammonia

Feed concentration (%) 90 It.5 0.15-0.17 13 0.11-0.11 60 12.5 0.09-1.10 18 0.10-1.11 40 15.0 0.05-0.07 20 0.07-0.08

Source: APRBRTC, 1986: 171

Experiment 2

Concentration of human excreta (%) 1 6 10 14 20 Survival days of schitosoma ova 21 15 15 7 7

Source: APRBRTC, 1986: 171

3 In China a temperature range of 16-60°C is considered as a thermophilic formentation. In practice 53°C is adopted as thermophilic.

4 The temperature adopted for mesophilic fermentation is 32-37°C

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These experiments indicate that higher feedstock concentration generate higher proportion of free ammonia which then accelerate the death of schistosoma ova.

Treatment of residual sludge from the digester:

It was mentioned earlier that ascaris ova settle in the residual sludge at the bottom of digesters. Disinfection of this residue was mentioned as a necessary step before applying in the Reid. It is estimated that about 50% of live acaris ova may be found in this residue. Some of the treatment methods developed in China and other places will be reviewed in the chapter on slurry treatment and composting.

4.4 Sanitary regulations

In Europe and North America there are strict regulations pertaining to the utilisation/disposal of slurry/sludge from biogas digesters involving seewage sludge and agricultural/human wastes. China has also developed such regulations. In China ascarias is one of the major diseases. Thus, the data on ascaris ova are commonly taken as the parasitological index. In areas where schistosomiasis and hookworm disease occur in epidemic forms, the ova of these pathogens are taken as reference index.

Bacteriological index based on Bacillus coil is developed. This index is used for the detection of other enteropathogenic bacteria that have similar characteristics and that live in manures.

These indices are used to determine whether or not the following sanitary regulations are followed:

• The retention time in digester must be 30 days, • The reduction rate of parasitic ova must be 95% or more, • No living ova of schistosome and hookworm should be found, • The breeding of flies and mosquitoes should be effectively prevented, • Scum and residue can be used as fertilizer only after disinfection, • The fatality rate of the ascaris ova should be 95°-100 • In case compost is adopted in treating residue, the period of composting should

be for 5-7 days with temperature of 5O-55°C, etc. (APRBRTC, 1986:164; ENFO, 1988:1)

4.5. Biogas slurry utilization and health and sanitary improvements:

The efforts in China have significantly contributed in the improvement of health and sanitation in rural China by systematically utilizing scattered garbage, pieces of straw and stalks.

A case study in a village before biogas adoption reports that hookworm infection registered 63.8%. The average egg count was 500/gram of faeces and the soil was infected with hookworm larvae. After biodigestion was adopted the hookworm infection declined to 4.07% within few years. The egg count decreased to 50 egg/gram of faeces. Similar results have been reported from other Chinese villages. Similar reduction is also reported in dysentery and enteritis cases. Within a few years dysentery and enteritis cases reportedly decreased by 80-%. Reduction of fly density by as much as 80.1 % is reported from some areas where biogas plants are adopted (ibid).

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4.6. Sanitation and public health aspects of slurry utilization in Nepal

In Nepal systematic studies in terms of" before' 'after' scenerious in the context of public health and sanitation have not been conducted. Some general reports have indicated the improvements of l general hygienic conditions' since the attachment of toilets to biogas plants (Castro et al, 1994:22; East Consult, 1994:33; 1996:34-35 ). East ConsuIt (1994) has also reported that all the plant owner respondents felt some reduction in odour due to toilet connection. In the 1996 study, East Consult has reported: 'Contamination of water source and soil have been reduced largely (JK). Diseases transmitted by water, air, dust and insects have also decreased appreciably....'(1996:34):

General literature on biogas normally claims a reduction in odour of faeces and other manures. From North America there comes a report that shows the application of anaerobic digestion in odour reduction of swine manure. According to this report (Welsh et al., 1977:22-26) anaerobic digestion at 35°C is more effective in reducing odour than anaerobic digestion at 25°C.

In Nepal, the Biogas Support Program (BSP) a biogas programme funded by the Netherlands Development Organisation (SNV), commissioned laboratory analysis of slurry compost, sun-dried slurry, fresh slurry, fresh slurry from toilet attached biogas plants (ATC, 1977). The parasitical and bacteriological test of toilet attached slurry from nine districts showed the presence of ova of three species of nematodes Ascaris lumbicoides, Trichuris trichuria (the report is not specific about which of the two species, Nectar americanus and Ancylostoma duodenaie, was present in the sample), one species of protozoa (Giardia lamblia) and one species of bacteria (Salmonella typhi). It is useful here to briefly mention the diseases associated with these organisms.

Ascaris lumbricoides:

Ascaris lumbricoides is a nematode worm that is distributed throughout the world. It is the largest of the human intestinal worm. An adult female measures up to 35 cm in length. Eggs, passed out in the stools may be transmitted to a host in contaminated food or drink. Larvae hatch out in the intestine and then undergo complicated migration, via the hepatic portal vein, liver, heart, lungs, windpipe, and pharynx, before returning to the intestine where they later develop into adult worms. The disease caused by this nematode is known as ascariasis. Adult worms in intestine can cause abdominal pain, vomiting, constipation, diarrhoea, appendicitis, and peritonitis; in large numbers, they may cause obstruction of the intestine. The presence of migrating larvae in the lungs can provoke pneumonia. Ascariasis occurs principally in areas of poor sanitation.

Trichuris trichuria (Whipworm}

Whipworm is a small parasitic whip-like nematode worm that lives in the large intestine. Eggs are passed out of the body with the faeces and human infection results from the consumption of water or food contaminated with faecal material. The eggs hatch in the small intestine but mature worms migrate to the large intestine. The diseased condition known as Trichuriasis occurs principally in humid tropical regions. Symptoms include bloody diarrhoea, anaemia, weakness, and abdominal pain. But these symptoms are evident only in heavy infestations.

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Hookworm

Although the ATC analysis does not indicate which species was detected in the samples, it should be noted that either of the two species Nector americanus and Ancyslostoma duodenale live as parasites in the intestine of man, and cause Hookworm disease. Hookworm larvae live in the soil and infect man by penetrating the skin. The worms travel to the large intestine and from there pass via the windpipe and gullet to the small intestine. Heavy hookworm infestations may cause considerable damage to the wall of the intestine, leading to a serious loss of blood; this in conjunction with malnutrition, can provoke severe anaemia. Symptoms include abdominal pain, diarrhoea, debility; and mental inertia. The disease occurs throughout the tropics and sub-tropics and is prevalent in areas of poor personal hygiene and sanitation.

Giardia lamblia

Germs of parasitic pear shaped protozoa inhabiting the small intestine of man. Gardiasis or lambliasis, the disease caused by this protozoa exhibits symptoms that include diarrhoea, nausea, belly ache, and flatulence, as well as the passage of fatty stools. Man becomes infected by eating food contaminated with cysts containing the parasite. The disease occurs throughout the world and is particularly common in children.

Salmonella typhii

Salmonella is a genus of motile rodlike gram-negative bacteria that inhabit the intestines of anima! and man and cause disease. Salmonella typhi causes typhoid fever. Other species cause various other conditions. This was the only bacterial species found by the ACT analysts from the 50 samples from various parts of the country

The ATC analysis found the ova parasitic worms in only 16% of the sample (in 8 out of 50 samples). Except for Trichuris trichuria and Giardia lamblia the egg counts were very low. The ATC report noted that the samples might have been collected during a period of lower microbial activity. An analysis of samples collected during the summer, notes the report, would have given a potentially different result of parasitic and bacterial presence.

Anyway, if the number and magnitude of parasitic and pathogenic presence in the toilet connected slurries are accurately represented in the report, the consequences for health and sanitation should not be so alarming. As shown in earlier part of the review in this chapter, human excreta is attributed to numerous pathogenic organisms, the numbers of species generally exceeding those found in animal manures. The lower number and magnitude of pathogenic species present in the Nepali sample could be due to the lower human excreta to cattle manure ratio in the digester input.

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CHAPTER 5

SLURRY TREATMENT

As the effect of different forms of slurry on crop production has been reviewed in Chapter 3, this chapter will deal with different forms of slurry with special attention to slurry composting.

5.1. Fresh liquid bioslurry

It is evident that the- biogas plant slurry is mostly used as manure with some additional applications as seed dressing agent and pesticide. Biogas slurry is also used in vermiculture and mushroom production as well as feed for cattle and fish. To delve into these areas is out of the scope of the present review.

By now it is evident that bioslurry in liquid from involves relatively minimal amount of nutrient loss. But bioslurry cannot be applied to the field the moment it comes out of the digester because efficiency can be obtained only when it is applied in phytophysiologically most advantageous times. This is perhaps the most important limiting factor for fresh liquid slurry application. As was reviewed in Chapter 3, fresh slurry has also the potential to cause eutrophication and toxic effects (e.g. H2S, ammonia concentration) on crops. In addition, as the preceding chapter has shown, concerns have also been expressed on the health and sanitation aspects of fresh liquid slurry, especially fresh liquid slurry derived from human excreta (Kshirsagar, 1986). Even if pathogen elimination in conjunction with the adoption of appropriate HRT is achieved, the application of fresh liquid slurry is still problematic in view of the unavailability/unaffordability of mechanical systems for fresh slurry application in South Asia. Even if application of slurry through irrigation channels is often advocated, lack of sufficient gradient, irrigation sources and channels, etc., are often the limiting factors.

Thus even if fresh liquid slurry is nutritionally superior, slurry researchers generally agree that utilisation in this form is not always applicable. Furthermore, if the slurry is derived from human excreta, fresh liquid application is even more problematic due to socio-cultural taboos associated with human faeces, at least in parts of South Asia (Patel, 1986). In addition, as already seen, some researchers are extremely cautious (Kshirsagar, 1986:37-43) about the health and sanitation aspects of utilising fresh liquid slurry from biogas plants fed with human excreta.

Surveys among farmers in Nepal (Castro et a!., 1994: 21-22; East Consult 1994: 35: DevPart 1998: 36; Gajurel et al., 1994:12) reported that farmers felt that the liquid slurry was not convenient for field application and that slurry was not always available at the time of field application. Another study (New ERA, 1995:22) reported that only 18% of the respondents used slurry in semi-liquid form. Only 4% of the respondents said that they used slurry after making compost.

A study in Nepal (New ERA, 1995:2) showed that 72 % of the farmers used slurry in dry form. A later study by DevPart (1996:36) reported that 64% of the biogas adopters were using slurry in dried form. A study by East Consult showed that 60% of the slurry users were using it in dried form. These evidences indicate that wet slurry is indeed an inconvenient form for utilization in the farm lands in underdeveloped countries like Nepal.

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5.2. Treatment of fresh slurry.

Slurry researchers largely agree that liquid slurry has to be treated to make it easier for handling and transportation; to enable it to be conveniently used according to the critical growth stages of crop plants, and to eliminate whatever parasitic/pathogenic organisms are left in it after the digestion. 'Treatment' here has both chemical and physical dimensions. Some of the treatment, methods are as follows:

5.2.1. Liquid slurry storage

Due to a multiplicity of reasons, slurry is not only dried it is also stored in liquid form. Generally, immediate application is neither warranted nor possible. The possible range of options are many. If nutrient conservation is one aspect, transportation and storage in large volumes are formidable for ordinary farmers in the third world.

The collection tank can be a brickwork storage basins or, if the soils are suitably impermeable, simple reinforced pits are constructed. Since complete liquid storage for extended storage periods would necessitate high storage volumes, usually only part of the bioslurry generated can be stored in this form. The size of the storage basin is determined by the amount of fertiliser needed at the time of application. If liquid application is planned, storage capacity is usually planned for few weeks. Storage basins with volumes ranging from 2 to 6m3 are generally recommended for small scale plants. For a smaller plant this should be adequate for even drying and composting (Demont, etal., 1991:29-30).

• Application of liquid slurry: In areas with relatively mechanised farm operations, the contents of the storage tanks are thoroughly agitated and filled into a liquidmanure spreader; or if the slurry is mobile enough, put through irrigation sprinklers (GATE, 1996). If the storage system is properly conserved and is not exposed to the sun little nitrogen is lost and this is the main advantage of liquid storage. On the other hand, as mentioned earlier, liquid storage requires a large storage capacity entailing high initial capital outlay. The practice of spreading liquid slurry also presents problems in that not only storage tanks are needed, but transport vessels as well, and the amount of work involved depends, in part, on how far the digested slurry has to be transported. For example, transporting one ton for a distance of 500 m in an oxcart takes about five hours (200 kg per trip). Distributing the dung over the field requires another three hours (GATE, 1996). Similar studies with liquid slurry is lacking, but in any case, handling and transportation of liquid slurry must be more difficult in the South Asian situation. One of the advantages of liquid slurry is that it can be spread uniformly in the field. Slurry researchers in India suggest that for basal dressing, bioslurry can be applied before sowing or planting and easily worked into the soil during tillage operation. If the crops are sown or planted in rows, bioslurry can be applied in furrows or seed holes (Demont et al., 1991:30). Careful covering of bioslurry after application prevents nutrient losses and enhances crop yield. For fruit and other perennial cultures, bioslurry should be applied around the plants and covered with mulch. Bioslurry in such cultures is not worked in order not to disturb the root system. The mulch layer prevents the bioslurry from drying out and promotes the absorption of nutrients by the plant. Bioslurry should be applied regularly during the vegetation period in accordance with the plant nutrient requirements. It is relatively easier to apply in the kitchen gardens due to their closer proximity to the biogas plants. However, it has often been suggested that fresh liquid bioslurry, especially if it is derived from human excreta, should be kept from coming into direct contact with harvested crops.

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Fresh liquid bioslurry derived from human excreta is also not advised for application (top dressing) in lettuce and vegetable crops {GATE, 1966, Kshirsagar, 1986).

5.2.2. Dehydration by sun drying

It is only possible to dry digested slurry as long as the rate of evaporation is substantially higher than the rate of precipitation (GATE, 1996). The main advantage of drying is the resultant reduction in volume (i.e. weight). Also it makes spreading possible. The cost of constructing a shallow earthen drying basin is modest. It can even be dried on a stable surface near the plant overflow (Demons 1991). On the other hand, drying results in a near-total loss of inorganic nitrogen (up to 90% , corresponding to roughly 50% of the total nitrogen content (Demont et al, 1991; GATE, 1996).

Due to the excessive moisture content (over 90%) of the slurry, sun drying is one of the most widely used slurry treatment practices in South Asia. It facilitates simple storage. Sun-dried slurry can be transported and applied like dung. It is not necessary to devise new application modes or arrange new transport equipment. In the drying process, the pits or beds are periodically filled with bioslurry, which is removed once the desired moisture content is reached. The drying process requires relatively large drying areas.

5.2.3. Filtration

In North America and Europe large sewage treatment plants and livestock operations use larger filtration systems (Haywood, 1997: 55-57). In others, methods like coagulation using either chemical, electrolytic or air flotation processes, or mechanical processes using vacuum drum filters, hot year drying etc., are in use. However these are not practical systems as far as farmers in South Asia are concerned. Filtration by employing sand, stones and leaf has been tried at few places but its practicality is yet to be established (Dhussa, 1986:31).

It has been reported (Kate, 1991: 10-11) that ammonia loss during direct sun drying could be reduced by using low grade apatite of single superphosphate.

In a process developed at IARI, the supernatant is removed from the top and the settled sludge is removed from the bottom of the digester. Broken leaves, sawdust or charcoal dust are used as absorbent and repeatedly soaked in the slurry. The drying process results into doubling the quantity of manure compared to drying of slurry alone. A further improvement of this process was accomplished at the Center of Science for Village (Wardha, India). The effluent slurry from the outlet of biogas plant passes over the organic bed arranged in the filtration tank and the water liquid flows out through an outlet placed at the far end and collects in a tank. Two such filtration tanks are made to run alternately (Kate, 1988 in Kate, 1991:1 I). It is reported that about 20 to 30% of the total water added to digester with cow dung is recovered and average moisture content of slurry is brought down to about 30-35% after two weeks of drying (ibid).

As elsewhere, Lakshmanan (1988) from Annamalai University in South India reports the result of an experiment involving gypsum, rock phosphate, calcium carbonate and burnt rice husk as absorbents. Among these materials gypsum added to the wet slurry at 25% of the weight of the slurry reduced the moisture content of the slurry by 30% (W/W) and reduced the loss of nitrogen by 1 7%. Kalia et al. (1994:22-24) reports the results of an experiment on low cost filtration pit for dewatering biogass plant slurry in the hills. The filtration materials used were 3-5 mm thick sticks of weeping wilow, bamboo, mulberry and kaigrass; the soiled contents of the slurry were found to have increased by 87%, 71%, 73% and 66% respectively after using these filters as compared to 29% in the slurry dried in conventional pit. The developed pit cost only Rs. 150 and provided easy way of dewatering slurry for its transport and for using the filtered water for mixing the fresh feedstocks. Goswami et

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al. (1996:23-26) reports on a simple low cost technology, involving the preparation of a straw-screen on a stout iron netting with mature rice straw, fresh neem leaves, and green weeds-- an improvement over the earlier IARI versions of dewatering technologies- from which they claim that 88% of the added water was recovered and the reuse of the water resulted in higher gas output. The recovered semi solid residue looked almost similar to fresh cow dung in its physical state for easy handling and disposal.

It is evident that biogas slurry can be directly applied to the farm land or dewatered to provide separate liquid fertiliser and solid residual product that can be composted or used as manure as such. The other alternative, the one practiced by most farmers in Nepal, is to use organic materials to use as moisture absorbents and use the resultant product directly as manure or for composting.

5.2.4. Centrifugation.

If the separation for high nitrogen content materials is required to be done dehydration and filtration methods cannot be effectively employed. If nitrogen rich biogas effluent is intended to be used as cattle feed centrifugation process should be employed to get moisture free solid without losing the nutritive value (Dhussa, 1986:111). Again the affordability of a centrifugation system in poor farming households is a problem.

5.2.5. Composting

Composting is the biodegradation of organic materials into a humus-like substance. Composting, as practiced by man is one of the more ancient of the agricultural arts. Traditionally, composting consisted of piling of readily putrescible materials such as garbage, nightsoil, animal manure and agricultural wastes with straw and leaves, and periodically turning the material as decomposition progressed. Composting remained more of an art than a science when Sir Albert Howard systematised the procedure in India (Price, Undated:! 35).

The review of effects of different forms of bioslurry on crop yield in Chapter 3 revealed the important nutritional role of composts on crop production. But the differences and similarities between aerobic composts and anaerobic digestates on the one hand and aerobic composts and composts prepared from anaerobic digestates (slurries/sludges from biogas plants) are far from being clear. Biocycle - The Journal of Composting Science reports that the differences are not clear even in North America. Journal contributor Riggle (1996:82) reports that even if anaerobic digestates contain higher nitrogen (because it is not volatilised during the digestion process) than aerobic composts, the need for a series of comparative trials is envisaged. The matter of systematic research in slurry/sludge/residual sludge composting is still in a very preliminary stage.

Nonetheless composted bioslurry is said to combine the advantages of both dried and liquid substrates:

• Matured bioslurry compost can be stored easily in windrows or heaps, and covered with large leaves (banana, coconut, etc.) or plastic foil to protect against rain or excessive evaporation.

• A composted bioslurry has a moisture content of only about 45% to 60%; it can be easily transported to the field in standard containers.

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• Losses of the plant nutrients available in the bioslurry are substantially minimized since most plant nutrients are incorporated by the microorganisms which decompose carbonaceous plant tissues.

• The use of different plant residues expands the number of plant nutrients in the final substrate {Demontetal. 1991:31).

• Composting can kill most of the remaining pathogens not eliminated during the anaerobic digestion process (see Khandelwal, 1986:105-109, APRBRTC, 1983:172-173; Ghosh 1986:146 among many others).Thus composting is also important from health and sanitation point of view.

5.2.5.1. Composting methods

Composting literature reveals that composting in the West is a highly mechanized process (Fairfield-Hardy Process, Mechanical Static Pile system, Silo-Counter Flow Aeration System, Rotating Drum Digester, Briquette System, to name a few). It is fruitless to go into the details of these systems for their lack of applicability in Nepal.

Modern composting is a biological process which operates under aerobic conditions. The process depends on the growth and activities of a mixed population of bacteria and fungi contained in the organic materials to be composted. When condition is favourable, the decomposition proceeds. Five fundamental parameters (common to all processes) essential to the composting process must be at optimum levels if aerobic/thermophilic composting is to proceed rapidly,, effectively and efficiently:

• Temperature: Composting involves both mesophilic and thermophilic temperature ranges which affect biological activity. At temperature below 40° C, the rate of reaction and efficiency of the process increases in proportion to increase in temperature. This is the range in which the mesophilic bacteria are active. The composting biomass initiates its activity at ambient temperatures, steadily builds heat as microorganisms begin to multiply, and the biomass undergoes degradation. When the mesophilic threshold has been achieved, the mass will remain at a plateau, then gradually rise in temperature until it reaches the thermophilic range. This plateau exists due to the acclimatisation and adaptation of organisms which are divided into mesophiles and thermophiles. As the temperature rise above 55° C, the rate of decomposition decreases, and very little activity takes place above 70° C (Price, Undated: 136).

• Aeration: Aeration determines whether the composting process is aerobic or anaerobic. It also determines the rate of the process; high-rate composting involves high-rate aeration, slow-rate composting involves slow-rate or minimal aeration (ibid: 137).

• Nutrient (Substrate) and Nutrient Balance: Generally the simpler the form in which the substrate occurs, the more rapid the decomposition occurs. To maintain adequate food for the microorganisms a balance of nutrients is required. The C:N ratio has been identified as significant; the optimum range for nearly all systems is 20- 25:1 (Gray, 1971:22).

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• Moisture Content: The optimum moisture content of the sludge-bulking agent (carbon carrier) mixture before decomposition has been found to be in the range of 50-60% (ibid).

• pH Level A profile of the pH level in a compost biomass indicates a drop in the pH from a level of pH 6-7 to pH 4-5 at the outset of biological activity in the mesophilic range. As decomposition proceeds the biomass becomes more alkaline till it reaches a stable level at around pH 8 (Epstein, 1977:5).

It has been generally accepted that biogas slurry is a good starter for composting. Experiments conducted at the Indian Agricultural Research Institute, Delhi, have shown that the digested slurry can be profitably used as a starter culture for composting other organic waste materials like leaves, straw etc. and in obtaining three times the quantity of manure than otherwise {Kate, 1991:12). It has been reported that only 10 litres of slurry is sufficient to compost 100 kg of agro-waste by employing semi-aerobic method of composting (ibid). Laura and ldnani{1977) composted wheat straw and sorghum fodder with digested slurry under anaerobic condition for 45 days and found that the addition of slurry accelerated decomposition of wheat straw and sorghum fodder from 10 to 30% and 15 to 40 % respectively (cited in Kate, 1991:12). The literature in the Asian context reveals the following major composting method using biogas slurry.

5.2.4.1 .a. Open Window or "Window' System

Before mixing the dried plant residues with liquid bioslurry a location and shallow should be selected near the biogas plant.

• One pan of dried plant residues should be soaked in 5-7 parts of bioslurry. One compost unit (a heap, pile or a windrow) should be set up in one day in order to guarantee the initiation of biological activity. The heat will begin to generate after 40 to 96 hours (Demont et al, 1991:32) (a bamboo or metal rod can be placed in the middle of the heap to see the temperature build up. Bare hands can grip the rod at 60°C. Compost thermometers are available but they are expensive for ordinary Nepali farmers). After several days the microbial reactions will shift from mesophilic to thermophilic and the temperature will raise up CD 7O°C This biotic heat kills pathogens and pathogenic ova (APRBRTC, 1983:172). An experiment from China reports that within 4 days, the temperature of the compost heap gradually increased from 31°C-32°C to 60°C, and when this temperature was maintained for 32 days ail ascaris ova died (ibid).

• In ordinary rural conditions, the dimension of a bioslurry compost heap should be around Ixixl.5m (height) and should not exceed 2.5 m in width or 1.8 m in height (Demont et al, 1991:32).

• The compost heap should be turned after 14 days. Turning of the pile permits cooling (mesophiiic) and assists in aerating the pile so that the metabolism remains aerobic and the moisture content adjusted to 60%. After several turns the temperature falls. The failure of the compost to increase temperature is used as a means to determine that the compost has been stabilised. Bioslurry compost with window method becomes ready for field application after six to ten weeks (APRBRTC, 1983:172). (After 15 weeks according to Demont, 1991:33).

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5.2.4.l.b. 'General composting' of bioslurry

The difference in this method is that the materials described above are directly piled on the ground without ventilation. Even if the temperature is lower than the open window system, experiments in China have shown that longer period of composting in this way can get rid of ascaris ova and other pathogens and ova.

Experiments in China (APRBRTC, 1986:173-174) have shown that addition of ammonia water raise the ammonia concentration in the compost. This ammonia permeates into the egg shell and shell membrane of ova and bacteria and kill them. With the addition of ammonia water at a concentration of 0.2%, schistosome cannot remain alive after six days. Addition of urea is also reported to perform the same function. A 0-4% urea water is needed to kill hookworm ova. The Chinese researchers have also reported that granular manure can be prepared by mixing the biogas slurry with 1.3% urea and fine soil. A reduced water content in these granules kill ova of ascaris and hookworm (ibid).

5.2.4.1.c. Pit composting of bioslurry

One often recommended practice in India and Nepal is to dig 2 to 3 compost pits (the size usually depending upon the capacity of the biogas plant) near the biogas plant. Slurry is allowed to flow over plant materials till these materials are wet with slurry. The slurry is then covered with plant materials. This process continues till the pit is filled. When the pit is filled -up completely it is covered with dry plant materials and soil. The pit so covered is somewhat higher than the ground surface. The pit is left in this condition for about a month. After this the materials in the pit are turned to facilitate aeration. The pit is again covered by plant materials and soil. Second and third tunings are done in an interval of about two weeks. Similar process is followed for other pit/s.

As was mentioned earlier biogas slurry is a good starter for compost making. Table 70 below shows that it takes less time for bioslurry compost maturation as compared to FYM compost maturation (both covered and uncovered). The 'Losses' (the report is not specific about what constitutes 'losses') is lowest in the biogas slurry pit composting as compared to FYM composting (both covered and uncovered). The highest loss is reported in FYM composting without cover.

Table 70: Comparison of FYM and biogas slurry pit composting Type of Manure Time taken for

maturing (days) Losses (%)

FYM composting without cover FYM composting with cover Biogas digested slurry (Spread over composting material)

120-150

90-100

60-70

45

20-25

7-10

Source: Myles, 1985: 27

In Nepal, Surveys have reported increasing trend of using pits for composting biogas slurry. A study conducted by Gajurel et al. (1994:11-12) reported that 40% of the respondents used slurry for composting. It is not sure whether ' composting' also meant the haphazard putting of manures and household wastes together. Karki et al. (1996:16) report that before the launching of the slurry extension pilot programme, there were very few compost pits. After the programme they found compost pits with a total volume of 7494 m3. They also found that the number of compost pits per biogas family averaged 1.4 and the size of the pits averaged 6.6 m3.

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DevPart (1996:35-36) reports that in 90% of the cases observed, slurry from the digester was directly led to compost pits. The farmers also reported to have told the researchers that if dry materials are added to the pits in the ratio of 1:4 (slurry: dry materials on w/w basis) moisture is absorbed by the dry materials.

Lack of time, labour and space seems to be some of constraining factors for pit slurry composting. Table 71 presents data on various constraining factors for pit slurry composting.

Table 71: Constraints faced by farmers for slurry compost making S.No Constraints Response

I Time 21 2 Labour 21 3 Space 13 4 Bedding materials 9 5 High water table 9 6 Diluted slurry 7 7 Wide distance from shed to pit 6 8 Negligence by farmers themselves 5

Source: Karki et al. 1996 :16 The perceived effects of bioslurry compost on crop production is largely theoretical as data for comparing fresh liquid slurry, sun dried slurry, bioslurry compost and ordinary compost are hard to find. As long as farmers' perceptions are concerned, studies in Nepal have shown that they usually they do not think that bioslurry compost has increased crop yield even if they feel that bioslurry compost was more potent (Britt et al, 1994: 42). From another study, Karki et al'. (1996:19) reported that 40% of the farmers were not sure about the superiority of slurry compost over FYM vis-a-vis crop yield (rice and potato). Table 72 below presents farmers feelings about the quality of slurry compost.

Table 72: Quality of compost against FYM S.No. Farmers' feeling Respondents Percentage

1 Superior to FYM 42 48 2 Inferior to FYM 1 1 3 Yet to see 35 40 4 No response 10 11 5 Total 88 100

Source: Karki et al. (1996: 19)

In terms of quality, the study found that around 24% of the farmers were not sure about whether or not slurry compost was a good manure (as compared to 64% who thought that slurry was a good' manure). Table 73 below presents farmers7 perceptions on the quality of slurry compost.

Table 73: Farmers' perceptions on the quality of slurry compost S.No. Quality of compost Respondents Percentage 1 Good 56 642 Bad 2 23 Yet to see 21 244 No response 9 105 Total 33 100

Source: Karki et al., 1996:14)

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It seems that the idea of superior manurial value of slurry compost (over FYM) is not a taken by all the farmers. Demonstration programmes can be effective in these situations.

The composition of slurry compost varies according to the different plant residues used to produce it. Table 74 presents data on the composition of slurry compost.

Table 74. General composition of slurry compost based on cattle dung based slurry

Constitution Percentage Dry-substance Organic carbon Total nitrogen Total phosphorous Total potassium

41-55 56-77 0.6-1.0 0.5-0.8 0.6-1.5

Source: Demont et al. 1991

There have been no systematic comparative studies of the nutritive quality of slurry composts based on slurries derived from different organic materials ( used as digester feedstocks). In addition, research is also lacking in the quality of slurry compost prepared from different organic materials as additive. One experiment from China reports on the effect of slurry compost prepared from phosphorous (phosphohumate). Table 72 below presents data from this experiment.

Table 75: Effect of biogas phospo-humate on major crops

Rice (2)* Wheat (13)* Sweet potato (3)* Rape (5)* Treatment Yield increase Yield increase Yield increase Yield increase jin/mu jin/mu % jin/mu jin/mu I % jin/mu jin/mu % jin/mu jin/mu %1. Check 581.5 ----- — 528.6 ..... .... 2772 ........ ... 246.0 —- ...2. Phosphorite powder 40-50 jin/mu

620.0 38.5 6.6 558.6 60.0 1 1.4 2959 !87 6.7 246.0 0 0

3. Digester sludge 400-1000 iin/mu

634.3 52.8 9.1 581.4 72.8 13.8 3250 478 17.6 260.2 14.2 5.8

4. Bio-gas phosphohumate

653.3 71.8 1.3 611.7 83.1 15.7 3302 530 19.1 258.0 22.0 8.9

Note: * The numbers in parenthesis indicate the number of experiments Source: APRBTC, 1983:158 1 jin = .5 kg; l mu = 0.667ha

Table 75 shows increased yield in wheat, sweet potato and rape with the application of phospho-humate. in the case of rice, digester sludge gave higher yield than phospho-humate. Higher moisture requirement for rice may be the reason.

5.2.5. Pathogen reduction by bioslurry composting

The assertions of majority of the slurry researchers have been that with composting the further reduction of pathogens/parasitic ova will take place. Thus bioslurry compost is taken as a product which has higher manurial value and which is safer, from health and sanitary aspects, for field application. Table 76 below provides data on pathogen elimination in aerobic digestion and composting.

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Table 76. Pathogen elimination and survivability in unheated anaerobic digestion and composting

Organism In-unheated anaerobic digestion In composing 1, Enteric May survive for over three months Killed rapidly at 60°C

2. Salmonellae May survive for several weeks Killed in 20 hrs at 60°C 3. Shigellae Unlikely to survive for more than

a few daysKilled in hr. At 55°c or in 10 dys at 40°c

4. E-Coil May survive for several weeks Killed rapidly killed above 60°C 5. Cholera May survive for one or two weeks Killed rapidly 55°C 6. Leptospire Survive for not more than two days Killed in 10 mts. At 50°C 7. Entamoebacysts May survive for three weeks Killed in 5 mts at 50°C and i day at

4O°C8. Hookworm ova Ova will survive Killed in 5 mts at 50°C in 20 hrs. At

SO°C and 200 hrs 45°C 9. Ascaris ova Ova will survive for many moths Killed in 2 hrs. At 55°C in 20 hrs.

At 50°C and 200 hrs 45°C 10. Schistosome Ova may survive for many months Killed in 1 hr 50°C 11. Taenia ova Ova will survive for a few months. Killed in 10 mts. Ai 58°C and in

over 4 hrs at 45°C Source: Navrekar, 1986:57 mts-minutes: hrs-hours

The above table shows that with appropriate retention time composting helps the elimination of many pathogens and parasitic ova. Composting of bioslurry thus contributes in the public health as well as better crop yield.

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Bibliography

Acharya, C.N., 1961. Preparation of Fuel Gas and Manure by Anaerobic Fermentation of Organic Materials. New Delhi: Indian Agriculture Research institute.

Acharya, C.N., 1953. 'Cow Dung Gas Plants.' Indian Fmg. N.S. 2 (9): 16-18; Acharya, C.N., 1952. 'Organic Manures.' I.C.A.R. Res. Rev. Ser. Bull. 2. New Delhi.

Adhikari, Poorna K., 1996. Effects of Biogas Plants on Family Health, Sanitation and Nutrition ( A Case Study in Lamjung District). Kathmandu: BSP, SNV-Nepal.

Asia-Pacific Regional Biogas Research-Training Centre (APRBRTC), 1983. Biogas Technology: UNDP-ESCAP-FAQ-CH1NA Biogas Training Course. Chendu, China.

ATC, 1997. Report of Laboratory Analysis of Manure Samples. Kathmandu: ATC

Berry, Walden. 1976. 'Where Cities and Farms Come Together'. In Merrill (ed.) Radical Agriculture, Mew York: Harper and Row

Berry, Walden. 1977. "The Agricultural Crisis as a Crisis of Culture'. In Gordon Douglass (ed.) 1984. Agricultural Sustainability in a Changing World Order. Boulder, Colorado: West view Press

Bhatta, A.P., A.K. Shukla and P.K. Dangi, undated. Performance of Bio-gas Plants in Mangalpur and Sharadan3gar Village Development Committees in Chitwan. Rampur,Nepal: 1ASS

Bhattarai, Mukunda P., 1990. Study Report for Detailed Biogas Potential in Dhading District. Kathmandu: Dhading Development Project.

Bhattarai, S., 1987. ' Report on the Observations on Effect of Effluent of Bobar Gas Plant on the Yield of Wheat Under Irrigated and Rainfed Condition.' Contribution from Sol Science and Agriculture Chemistry Division for the Winter Crop Seminar, Aug. 14-17, 1978). Kathmandu: Division of Soil Science and Agricultural Chemistry

Bhattarai, S. and S.L. Maskey, 1988. 'Effect of Azotobactor Inoculation in Combination with Different Sources of Organic Manures .' Proceedings of National Conference on Science and Technology, April 24-29, 1988, pp 81-85. Khumaltar, Kathmandu: Division of Soil Science and Agricultural Chemistry

BMZf GTZ, BOARDA, Ministry of Energy, DNES, and UNDARP, 1990. International Conference on Biogas-Technologies and Implementation Strategies (Report) Pune, India.

Britt, Charla, 1994. The Effects of Biogas on Women's Workloads in Nepal: An Overview of Studies Conducted for the Biogas Support Program Kathmandu: BSP.

Britt, Charla, 1994. The Effect of Biogas on Women's Workloads in Nepal: An Overview of Studies Conducted for the Biogas Support Programme. Kathmandu: BSP.

80

Bulmer, A., John Finley, David Fulford, and Namie M. Lau-Wong.1985. Biogas-- Challenges and Experience from Nepal Vol. 1,11 Kathmandu, Nepal: Mnited Mission to Nepal.

Campino, 1990. The Effect of Nitrogen from Liquid Manure, Bioslurry and Urea on Hay and Maize in Tropical Columbia.' In Biogas Forum, Vol 1 special.

Chanakya, H.N., 1986. 'Nighsoil Biogas Plants: Health Aspects and Design.' In Biogas from Human Waste. (Workshop Report) New Delhi: CORT.

Chawla O.P., 1984. ' Manurial Aspects.' Advances in Biogas Technology. New Delhi: ICAR.

Consolidated Management Service Nepal (P). Ltd., 1996. District Level Training Manual on Biogas Technology. Nepai: FAO/TCP.

Consortium on Rural Technology {CORT) , 1993. Biogas Slurry Utilisation. (Seminar Report) New Delhi: CORT.

Consortium on Rural Technology (CORT) , 1986. Biogas from Human Waste. (Workshop Report) New Delhi: CORT.

Cott, A.M, 1974. ' Anaerobically Digested Pig Slurry as Resource for Crop Production.' Anaerobic Digesiion MIRCEN, Vol. No. 1, 1984 page 85-86.

Daize, Hu, Meng Xun, Yang Kejun and Ren Shengquing, 1991. 'Bio-Digestion - the Pivot of China's Eco-agricultural Construction.' In Biogas Forum Vol. II, No. 45, 1991.

Dayal, M. 1986. ' Keynote Address,. In Biogas from Human Waste. (Workshop held in Delhi) Delhi: Consortium on Rural Technology.

de Castro, J.F.M., A.K. Dhussa, J.H.M. Opdam and B.B. SNwal. 1994. Mid-Term Evaluation of the Biogas Support Program. Kathmandu: Dutch Directorate for International Cooperation

Demont, D., A. Sckeyde, and A. Ulrich, 1990. ' Possible Applications of Bioslurry for the Purposes of Fertilisation.' In Biogas Forum , Vol. 1 Special.

Department of Science and Technology, Govt. Of India, 1981. Biogas Technology and Utilization: A Status Report. New Delhi: DST.

Demont, D., A. Sckeyde, and A. Uirich, 1991. ' Possible Applications of Bioslurry for the Purposes of Fertilisation.' In Changing Villages, Vol. 10, No.l, ]an-Mar., 1991.

Demant, Dierk. 1990. ' Biomanure from Small Biogas Plants'. In gate 2/90

Demuynck et al, 1984. Biogas Plants in Europe: A practical Handbook (Solar Energy R and D in the European Community) Series e, Volume 6 (Energy from Biomass). Dordrech, Holland: D. Reidel Publishing Company (for the Commission of the European Community).

Desai, S.V. and S.C. Biswa, 1945. 'Manure and Gas Production by Anaerobic Fermentation of Organic Wastes.' Indian Fmg. 6:67-78.

Desai, S.V. and S.C Biswas, 1964. 'Combustible Gas from Cow Dung.' Indian Fmg. July, 1946:140-43.

81

DevPart - Nepal, 1996. Final Report of Impacts of Biogas on Users. Kathmandu: BSP.

Dhussa, A.K., 1985. ' Biogas Plant Effluent Handling and Utilisation.' in Changing Villages Vol.7, No.l.

Dhussa, A.K., Raymond Myies, and Nasae Canada Lmisae, 1985. 'Design and Implementation of a Pilot Demonstration Community Night Soil Biogas Scheme.' in Changing Villages Vol.7, No.5.

Dhussa, A. 1986. 'Nightsoil based biogas plants'. In Biogas from Human Waste. CORT: Delhi

Dhussa, A. 1986.' Biogas plants effluent handling and utilization'. In Biogas from Human Waste. CORT: Delhi

Droogers, P. And }. Bouma, 1996. ' Biodynamic vs. Conventional Farming Effects on Soil Structure Expressed by Simulated Potential Productivity.' in Soil Science Society of America Journal Vol. 60 No. 5.

EastConsuIt (P) Ltd., 1994. Final Report BSP Biogas Users Survey -1992/93. Kathmandu: Biogas Support Programme, ADB/N, SNV-Nepal, GGC.

EastConsuIt (P) Ltd., 1996. Biogas Users Survey 1994-1995. Final Report Biogas Support Programme (A Joint Programme of Recognized Biogas Companies, ADB/N, RBB, NBL and SNV-Nepal. Kathmandu: BSP.

Ef-Halwagi, M.M., 1980. ' The Development and Application of Biogas Technology in Rural Areas of Egypt. National Research Center, Egypt: Applied Science and Technology Project No. 263-0016.

ENFO, 1988. Chinese Biogas Digesters.' In Environmental Sanitation Information Center. Bangkok: AIT.

Fair, G.M., 1934. * Digestion of Garbage.' Journal of Sewage Works. 6:259-61.

Farrinton, J. and Adrienne Martin. 1990. Fanner Participation in Agricultural Research: A Review of Concepts and Practices. Agricultural Administration Unit Occasional Paper 9, London: Overseas Development Institute

FAO, 1975. Organic Materials as Fertilizers (Report of an expert consultation held in Rome, 2-6 December 1974). Rome: FAO.

Fowler, G. J and G. W. ]oshi,1923. "Studies on the Fermentation of cellulose.' Journal of Indian institute of Science, Banglore 3:39.

Frossard, E., S. Sinaj, L-M Zhang, and JX. Morel, 1996. "The Fate of Sludge Phosphorus in Soil-Plant Systems.' In Soil Science Society of America Journal, Vol. 60, No. 4, 1996.

Fulford, D.J. 1978, Biogas in Nepal -- The State of the Art. Butwal, Nepal: UMN

Gajurel, Om. P., Wim J. van Nes, and Basudev Neupane, 1994. Survey 1990-91 on GGC Biogas Plants. Butwal: Gobar Gas Company Research Unit, Nepal.

Garde, R.V., D.R. Ranade and S.H. Godboie, 1985. 'A Note on Survival of Saimonellas during Anaerobic Digestion of Cattle Dung.' In Biogas Forum No. 29.

82

Gaur, A.C. and K.C Dhandelwal, 1986. "Manure from Anaerobic Treatment of Human Waste/ In Biogas from Human Waste (Workshop Report). New Delhi: CORT.

gate, 1996. ' Sludge ~ Management'" .In Internet Website htt://www.gtz.de/gate/isat/at-info/biogas/appldev/sl udge.html

Geoffrey, Barnard, 1985. Agricultural Residues as Fuel in the Third World. Earth Scan: International Institute for Environment and Development, The Beijer Institute, The Royal Swedish Academy of Sciences, Energy Information Program. Tech. Report No. 4. London: IIED.

Gerretsen, F.C. and H.de Hoop, 1957. 'Nitrogen Losses during Nitrification lb Solutions and in Acid Sandy Soils, in Can. J. Microbiol, 31, pp. 359-80. 1957.

Ghosh, S.I986. Prologue'. In Biogas from Human Waste. CORT: Delhi

Goswami, K.P., P.S. Bhorania and K.P. Patel, 1996. ' Recovery of Water and Manure From Biogas Plant Slurry.' In Changing Villages, Vol. 15, Jan-June

Gnanamani , A. And R. Kasturi Bai, 1993. 'Carbon and Nitrogen Transformation of Biodigested Slurry.' In Biogas Slurry Utilsation. New DeIhi:CORT.

Gupta, D.R., 1991. 'Bio-Fertilizer from Biogas Plants/ In Changing Villages, Vol. 10, No.l. Jan-Mar., 1991.

Gupta, D.R., 1986. x Biogas from Human Waste: Public Health and Social Aspects.' In Biogas from Human Waste (Workshop Report). New Delhi: CORT.

Gurung, Jit B. 1997. Evaluation of Farmer Participatory Action Research in Bhumlichwok VDC, Gorkha. (Report prepared for GDP/GTZ Nepal). Kathmandu: Deva Pvt Ltd.

Gutterer, Bernd and Ludwig Sasse, 1993. ' Summary and Recommendations/ Report Biogas Survey 1992: Cross Section Analysis of Biogas Dissemination Programmes. Bremen, FRG: BORDA (Bremen Oversees Research and Development).

Haywood, Frank, 1997. ' Handling Liquids and Solids on Hog Farms.' In BioCycIe Vol. 9, March.

HMG/ Nepal and SNV-Nepal, 1996. Proposal: Biogas Support Programme Phase III. Kathmandu: BSP. Nepal.

House, D., 1978. The Compleat (sic) Biogas Handbook, Aurora: VAH1D, CR7002, USA.

Innotti, E.L., J.H Porter, ]. R. Fisher and D.M. Siever, 1979. 'Changes in Swine Manure Anaerobic Digestion/ In Development. Ind. Microbiol., 20:519-529.

Institute of Soil and Fertilizer, 1979. 'The Utilization of Research Work on Digester Sludge and Effluent as Fertilizer/ in Biogas Technology and Utilization- Chengdu Seminar, Sichuan Provincial Office of Bio-Gas Development.

Isman, M., 1950. ' line etude sur les modes d'utilization pratique des appareils a gaz de fumier. Elevage of Cult. 21, October, 1950.

]arvis, S.C., 1996. "Future Trends in Nitrogen Research.' In International Journal on Plant and Soil Relationship 181:196. Dordrech: Kluwer Academic Publishers, Netherlands.

83

Jianmin, Fan, Liu Changix and Cao Shangxue, 1992. 'Effect on the Production and Quality of Beileil Tobacco by Applying Biogas Fertilizer.' In Biogas Forum Vol (2) special. [Excerpted from China Biogas, 1991, 9 (3), 34-35, translated by Ren Shengquing.

Jiashi, Sun and Zhu Reng, 1991. 'A Study on Applying "Biogas Fertilizer" to Prevent Plant Disease and Insect Pests.' In Biogas Forum, Vol. 11 Special. [Excerpted from China Biogas, 8(4), 31 -33, 1990, translated by Ren Shengquing]

Joshi,N.V., 1945. Pres. Add. Agric. Sec, Proc. Indian Sci. Congr. Nagpur, 32 (2):219-21.

Kalia, Anjan K. And S.S. Kanwar, 1994. 'Filtration Pit for Dewatering Biogas Plant Slurry in Hills.' In Biogas Forum, Vol. I, No. 56.

Kanthaswamy, V., 1993. ' Effect of Bio-Digested Slurry in Rice.' In Biogas Slurry Utilsation. New Deihi:CORT.

Kanwar, S.S., Harsh Nayyar, D.P. Walia, 1993. Influence of Biogas Slurry on Germination and Early Seedling Growth of Bread Wheat.' In Biogas Forum, Vol. Ill, No. 54.

Karki, Krishna B. And Bhimsen Gurung, 1996. Evaluation of Biogas Slurry Extension Pilot Programme. Kathmandu: BSP, SNV-Nepal.

Kate, Tarak, 1991. 'Utilization of Anaerobically Digested Biogas Effluent Slurry or Sludge.' In Changing Villages Vol. 10, No. 1 Jan-Mar., 1991.

Keizer, Cecilia, 1966. Effect of Biogas on the Workload of Women in Nuwakot District in Nepal. Kathmandu: SNV-Nepal.

Keefer, C.E. and H. Kartz, Jr., 1 934. * The Digestion of Garbage with Sewage Sludge.' Journal of Sewage Works, 6: 14-23, 250-25.

Ketkar, CM. , 1993. Use of Biogas Slurry in Agriculture.' In Biogas Slurry Utilsation. New DelhkCORT.

Keyun, Deng and Choi Yunchu, 1990. "China Actively Promotes the Development of Biogas Technology." In International Conference o Biogas: Technologies and Implementation Strategies ( Conference Report, Pune India: a Joint Initiative of FRG and Republic of India, Jan. 10th to 15th, 1990).

Khandeiwal, K. C. and S. S. Mahdi, 1986. Boigas Technology: A Practical Handbook Vol. I. New Delhi: Tata McGraw.

Khandelwal, K.C., 1981. 'Promotion of Biogas System: Problems and Prospects.7 Seminar Com Workshop on Janata Biogas Technology and Fodder Production. Karnal: NARI.

Kijne, Eric, 1984. Biogas in Asia Ultrecht, Holland: CDP (Consultants for Management of Development bv).

Kogblevi, A., 1987. "Biodigester Effluent Boosts Up Vegetable Production in Benin.' In Biogas Newsletter No. 25, November, 1987. [Excerpted from Directeur du Centre National d'Agropedologie, B.P. 988, Cotonou, BENIN, July 1985).

Kololgi,S.D., S.S. Nagalikar and L.V. Hirevendkanagoudar, 1993. ' Effect of Biogas Slurry in Crop Yield/ In Biogas Slurry Utilsation. New DeIhi:CORT.

84

Kone, Siaka, 1991. ' Contamination of Bioslurry.' In Biogas Forum Vol. IV. No. 47.

Kshirsagar, S.R., 1986. ' Nightsoil Biogas Plants: Health Aspects.' In Biogas from Human Waste (Workshop Report). New Delhi: CORT

Kuppuswamy, G., A.R. Lakshmanan and A. Jeyabal, 1993. "Effect of Biogas Slurry on Rice-Blackgram Cropping System.' In Biogas Slurry Utilisation. New DeihhCORT.

Latif, Ch. Magda Yassien abd el, 1990. Implementation Strategies and Biogas Technologies Applied in Egypt.' In International Conference on Biogas. Jan. 10-15, 1990. Pune, India

Laura, R.D. and I.Idnani. 1972. "Effect on wheat yield and nitrogen uptake from manures made from manures made from spent slurry'. In Plant Soil.32:283-295

Laurie, J.P., 194]. Methane-its Production and Utilization. London: Chapmann and Hall.

Lakshmanan, A.R.,1988.1 A report communicated at the R ST. D review meeting organized by the DNES, Banglore

Lakshmanan, A.R., G. Kuppuswamy and A.Jeyabal. 1989.' Seed coating with biogas slurry and bio fertilizers on blackgram'. In Microbiological Abstracts (31st Annual Conference of Microbiologists of India, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu. p. 106-107)

Laxamanan, A.R., G. Kuppuswamy and A. Jeyabal, 1993. I Use of Biogas Effluents as Seed Coating Media for Successful Crop Production/ In Biogas Slurry Utilsation. New DeihhCORT.

LI, N.G., 1982. Is the Xinbu System Economically Feasible? Unpublished Manuscript.

Madan, Savitri, 1986. 'Nightsoil Based Biogas Plant: Its Role in Social Equality and Community Benefits and the Problems of its Social Acceptance.' In Biogas from Human Waste (Workshop Report). New Delhi: CORT.

Mahapatra, Krishna, 1985. 'The Puri Nightsoil Biogas Plant: A Sociological Evaluation Through A Case Study.' in Changing Villages Vol. 7 No.6, Nov-Dec.

Mapuskar, S.V., 1991. Acceptance of Biogas from Human Nightsoil/ In Changing Village Vol. 10, No. 3.

Mapuskar, S.V., 1986. 'Nightsoil Based Biogas Plants: A Useful Device for Rural Health and Development. In Biogas from Human Waste (Workshop Report). New Delhi: CORT.

Maramba, Felix D., 1978. Biogas and Waste Recycling: The Philippine Experience. Manila: Maya Flour Division, Liberty Flower Mills.

Martin-Leake, H. And LE. Howard, 1952 (a). Methane Gas from Farmyard Manure. Albert Howard Foundation of Organic Husbandry (England): Publ.No.9.

Maskey, S.L, undated. Manurial Value of Biogas Slurry: Some Observations. (Paper presented at International Workshop on Microbiologial aspects of Biogas production. May 31-June3,Kathmandu).

85

Mohan, S. And M. Gopalan, 1994. % Biogas from Cow-dung for Insect Control During Storage/ In Biogas Forum (1994) Vol II, No. 57. [Excerpted from Bioresource Technology, Vol. 39, No. 3, 1992, pp. 229-232.].

Moulik, T.K., 1990. 'Diffusion of Biogas Technology: Strategies and Policies.' In GATE 11, 15-3-6.

Myles, R.M., Rajen Sundaresan and T.C. Sharma, 1993. ' Biogas Slurry Experiment.' In Biogas Slurry Utilsation. New Delhi:CORT.

Myles, R.M., 1985. ' Strategy for Promotion of Biogas Plants from Human Waste in Rural Areas.' in Biogas from Human Waste (Workshop Report). New Delhi: CORT

Myles, R.M., 1985. A Practical Guide to Janata Biogas Plant Technology. New Delhi: AFPRO, India.

Navarro, J. Diaz, 1984. ' Slurry as Bio-fertilizer.' In Biogas Forum No. 16, 1984.

Navrekar, S.M., 1986. ' Biogas From Nightsoil: The Health Aspect and Design.' In Biogas from Human Waste (Workshop Report). New Delhi: CORT.

Nayyar, Harsh, S.S. Kanwar and D.P. Walia, 1993. ' Effect of Biogas Slurry as Seed Dressing Agent on Seed Performance of Maize and Rice.' In Biogas Forum Vol. !V No. 55.

Neelakantan, S., 1981. ' Chemical Composition of Cattle Excreta and Its Manurial Value/ Seminar Com Workshop on Janata Biogas Technology and Fodder Production. Karnal: NAR1.

Neelakantan, S., 1981. "Principles and Application of Anaerobic Fermentation and Biogas Production. Seminar Com Workshop on Janata Biogas Technology and Fodder Production. Karnal: NDRI.

New ERA, 1995. Survey of Users of Biogas Plants in Nepal. Kathmandu: BSP. New ERA, 1985. Biogas Plants in Nepal An Evaluative Study. Kathmandu: Unicef.

Parikh, Rahul, 1989. ' Garbage Gas Manure Plant.' In Changing Villages Vol. 8, No.4, Oct.-Nov, 1989.

Parikh Jyoti K. And Parikh Kirit S., 1976. "Mobilization and Impacts of Bio-gas Technologies/ In Energy (The International Journal) Voi.2., No. Great Britain: Pergamon Press.

Patel, Ishwarbhai, 1986. 'Social Aspects of Nightsoil Biogas/ In Biogas from Human Waste (Workshop Report). New Delhi: CORT.

Patel, J.J., 1951. 'Digestion of Waste Organic Matter by Production of Methane and Organic Fertilizer and a New Economic Apparatus for Small Scale Digestion (Gram Laxmi)/ Poona Agriculture College. Mag. 42 (3): 150-59.

Myles, Raymond, 1982. Biogas Technology. New Delhi: Action for Food Production

Riggle, David, 1997. ' Anaerobic Digestion Gets New Life on Farms/ In BioCycle, January, 1997.

Riggle, David, 1996. "Anaerobic Digestion for MSW and Industrial Wastewater.' In BioCycle, November, 1996 .

86

Rajagopal, R. and N. Chitra, 1992. 'Environmental Impacts of Bio-energy/ In Energy Environment Monitor Vol. 8, No. 1, 1992.

Robin, Gregory and Juliana Hinterberger, 1990. ' Biogas Unit Slurry as a Fertilizer: The Experience in Donimica.' In Biogas Forum, Vol. Ill, No. 42., 1990.

Rosenberg, G.7 1952 (a). Methane Production from Farm Wastes as Source of Tractor Fuel.' Journal of Min. Agric. (England) 58: 487-94.

Sankaran, K.; G.V. Kothandaraman, and T.S. Manickam. 1981. ' Comparative study of biodigested slurry as source of organic plant nutrient'. Coimbtore ; Tamilnadu Agricultural University (Presented in a seminar in microbiology of biogas fermentation).

Sankaran, K and K. R. Swaminathan.1988. Residual impact of biodigested slurry as source of organic manure'. In Management and Utilization of Slurry. Himansulu Publications

Santosh, Y.S. Satya, R. S. Arya and P. Vasudevan, 1993. ' Biogas Slurry-Production and Utilization in Agriculture.' In Biogas Slurry Utilsation. New DelhhCORT.

Sathianathan, M.A. 1975. Achievement and Challenges. New Delhi: Association of Voluntary Associations.

Schulz, Heinz, Dr., 1990. 'Agriculture Biogas Plants and the Use of Slurry as Fertilizer in the Federal Republic of Germany/ International Conference on Biogas Technologies and Implementation Strategies Report. January 10-15, 1990, Pune, India.

Scott, J.M.,1989. 'Seed coatings and treatments and their effects on plant establishment'. In Advances in Agronomy, 42-43-83.

Schreeg, Thomas M. And D. Lyle Jarrett, III, 1996. 'Biosolids Cut Fertilizer Costs by $200 an Acre/ In Biocycle, October 1996

Shen, R.Z. 1985." The utilization of biogas digester in China'. In 'Aerobic Digestion, 1985' (Proceeding of the 4th International Symposium on Anaerobic Digestion. Ghogzhou, China).

Shen, R.Z. et. al. 1988. Study on the application of AFP and AES with anaerobically fermented residues to prevent Barley Yellow Mosaic Virus'. In 'Anaerobic Digestion, 1988' Tilohe and A. Rozzi (eds.). (Proceedings of the 5th International Symposium on Anaerobic Digestion, Bologne, Italy).

Shiva, Vandana. 1988. The Violence of the Green Revolution: Ecological Degradation and Political Conflict in Punjab. London Zed Books

Sindhu, B.S. and V. Beri, 1989. 'Effect of Crop Residue Management on the Yields of Different Crops and on Soil Properties.' In Biological Wastes 27 (1989). England: Elsevier Science Publisher.

Singh, ]. B. 1989. ' Biogas Slurry Manure/ In Changing Villages Vol. 8, No. 3, (Aug, 1989). Singh, ]. B.I990 ' Biogas Slurry Manure/ In Changing Villages Vol. 9, No. 3, (]uly-Aug) 1990. Singh,]. B. ' Biogas Slurry Manure/ In Changing Villages Vol. 10,No.l (Jan.-Mar.), 1991.

87

Singh, Harpal, 1995. ' Indian Advances in Biogas Technology- Review of Work Done under A1CRP On RES.' In Biogas Forum Vol. I, No. 60, 1995.

Singh, Shiv. P., H.N. Verma, D.K, Vatsa and A.K. Kalia, 1995. ' Effect of Biogas Digested Slurry on Pea, Okra, Soybean and Maize/ In Biogas Forum Vol. IV, No.63, 1995.

Singh, Y . 1986. 'Health Aspects of Anaerobic Digestion'. In Biogas from Human Waste Delhi: CORT

New ERA. 1995. Survey of Users of Biogas Plants in Nepal. Kathmandu: BSP

Tarn, D.M. and N.C. Thanh, 1983. ' Biogas Technology in Asia: The Perspectives/ In Renewable Energy Review Journal Vol. 5, No.l, April 1983. Bangkok: Asian Institute of Technology.

Tentscher, W., 1985. 'Digested Effluent as Fertilizer'. Anaerobic Digestion, M1RCEN, Vol 3, No. 2, 1986, Page 136.

Theilen, Udo, 1990. ' Biogas-An Appropriate Technology or Third World Countries/ In GATE, 1 1-15-3-6.

Thysen and Bunker, 1927. Microbiology of Cellulose, Hemicelluloses, Pectins and Gums. London: Oxford University Press.

Tripathi, A.K., 1993. Biogas Slurry - A Boon for Agriculture Crops/ In Biogas Slurry Utilisation. New Delhi:CORT.

UMN/Nepal, 1985. Biogas-- Challenges And Experience From Nepal Vol. I. Kathmandu: UMN.

UMN/Nepal. 1985. Biogas-- Challenges and Experience from Nepal Vol. 1,11 Kathmandu, Nepal.

Vaidya, A.K. and K.D. Joshi, 1996. 'Animal Housing Improvement Programme and Biogas Plants: A Users' Assessment.' LARC Working Paper No. 96/40.

van Brake!, ]., 1980. The Ignis Fatuus of Biogas. Small Scale Anaerobic digesters ("biogas plants"): a critical review of the pre-1970 literature Delft, the Netherlands. Delft University Press.

van Nes, Wim ]., 1996. ' Biogas Support Programme: Results in the Period July 1992-1995. In Biogas and Natural Resource Manangement (BNRM) Nepal No. 51, April 1996.

van Nes. Wim ]. Undated. - proper use of Slurry' Kathmandu: BSP

Vargas, A.M., 1986. 'Regulation of Vegetation Growth Through Biogas Effluent/ Biogas Newsletter, No. 23, November 1986.

Verma, O.S., 1981. ' Operational System of Govar Gas in Rural India/ Seminar Com Workshop on Janata Biogas Technology and Fodder Production. Kamal: NARI.

Verma, O.S., 1981. ' Profitability of Biogas Plant.' Seminar Com Workshop on ]anata Biogas Technology and Fodder Production. Karnal: NARI.

Vogtmann, H. And J.M. Besson, 1979. ' European Composting Methods: Treatment and Use of Farm Yard Manure and Slurry/ Compost Sci./Land Uttil., 19(1): 15-19.

88

Waksman, S.A, 1932. Principles of Soil Microbiology, 2nd ED. Baltimore: Williams and Wilkings Co. Inc.

Welsh, F.W., D.D. Schulte, E.J. Kroeker, and H.M. Lapp, 1977. The Effect of Anaerobic Aaerobic Digestion upon Swine Manure Odors.' in Canadian Agricultural Engineering, Vol. 19, N0.2, December.

WECS.1974. Energy Synopsis Report Nepal 1992/93. Perspective Energy Plan, Supporting Document No.1 Report No.4/4/270494/1 /I Seq. No.451. Kathmandu: WECS

Zhicheng, Ye, 1991. ' Utilization of Biogas Slurry to Soak Seed Has Achieved a Remarkable Result/ In Biogas Forum, Vol.2/special. [Excerpted from China Biogas, 8(3), 41-42, 1990, translated by Wu Libin].

89

General references

(Not cited in the text)

Acharya, C.N., 1935. ' Studies on the Anaerobic Decomposition of Plant Materials.' Biochem.

Acea, MJ. and T. Carballas, 1988. * Effects of Cattle-Slurry Treatment on the Microorganisms of the Carbon- and Sulphur- Cycles in the Soil.' In Biological Wastes 24 (1988)251-258. England: Elsevier Applied Science Pulbishers Ltd., GB.

Anonimous, Undated: Proper Use of Biogas Slurry.

Bahadur Shahzad, 1981. Seminar-corn- Workshop on Janata Biogas Technology and Fodder Production. Karnal: NDRI.

Bala B.K. and M.A. Satter, 1990. 'Kinetic and Economic Considerations of Biogas Production Systems.' In Biological Waste 34 (1990) 21-38.

Brklacich, M. and Others, 1991. "Review and Appraisal of Concept of Sustainable Food Production Systems.' In Environmental Management Vol. 15, No. 1. New York: Spring-Verlag Inc.

Brown, Norman, 1987. ' Biogas Systems in Development.' In Appropriate Technology Vol. 14, No.3. London: IT Publications Ltd.

Brunding,5.G. and L.K.K. Rodhe, 1995. 'Comparison of Manure Handling Systems under Swedish Conditions.' In AgBiotech News and Information Vol. 7, No. 1. [Excerpted from Journal of Agricultural Engineering Research, 1994, 58 (3)].

Cacciatore, David A. and Mefanie A. McNeil, 1995. 'Principles of Soil Bioremediation.' In BioCycle Vol. 8, No. 10.

Carrion Perez, P and R. Martinez Ramirez, 1995. ' Fermentation Process of Compost Controlled by a PC In Waste and Organic Byproduct Processing Vol.7 No.l. {Excerpted from TEA Produccion Vegetal, 1994, 90 (1).]

Chakraborty, Amulya, 1986. 'Biogas Plants Based on Nightsoil.' In Biogas from Human Waste. (Workshop Report) New Delhi: CORT.

Daily, Gretchen C. And Paul R. Ehrfich, 1991. " Socioeconmic Equity, Sustainbility, and Earth's Carrying Capacity.' In Ecological Applications, 6(4), 1996. Washington D.C.: ESA.

Daize, Hu, Meng Xun, Yang Kejun and Ren Shengquing, 1991. "Bio-Digestion - the Pivot of China's Eco-agricultural Construction.' In Biogas Forum Vol. 11, No. 45, 1991.

DaSilva, Edgar ]., 1981. Biogas: its Potential and Applications for Developing Countries.' In StamboHs, Costis, ed., Renewable Energy Sources for Developing Countries. London: Heliotechnic Press.

Demant, Dierk, 1990. ' Biomanure from Small Biogas Plants.' In GATE 11,15-3-6, 1990.

Demant, D., 1986. ' Use of Digested Slurry From Biogas Plants.' In Biogas Forum No. 27, 1986. Kathmandu.

90

Dev, S.P., M.K. Gupta and K.K.R. Bhardwaj, 1992. " Effect of Crop Waste and Nitrogen Levels on the Number and Activity of Microorganisms in Soil in Wheat- Maize Cropping Sequence.' In Biological Nitrogen Fixation and Biogas Technology. Tamilnadu: Tamilnadu Agricultural University.

Devkota, Govinda P., 1982. "Report on Second Inspection Visit to Dome Design of Gobar Gas Plants Constructed in Pokhara, Nepal/ In Biogas Forum:

Dewes, T., L.Schmitt, U. Valentin and E. Ahrens, 1989. "Nitrogen Losses during the Storage of Liquid Livestock Manures.' In Biological Wastes 31. England: Elsevier Science Publishers Ltd.

Dhanpai, D., 1992. ' Rural Energy and the Quality of Air-with Special Reference to a Tribal Area in Tamil Nadu. In Energy Environment Monitor Vol. 8 No.l, 1992.

Dhussa, Anil. K.; 1986. " Biogas Plant Effluent Handling and Utilisation.' In Biogas from Human Waste. (Workshop Report) New Delhi: CORT.

Dohne, E., 1990. ' Optimal Bioslurry Fertilisation in West Germany.' In Biogas Forum, Vol. 1 Special, 1990.

Domsch, K.H. and et al., 1979. 'A Comparison of Methods for Soil Microbiai Population and Biomass Studies/ In Eingegangen. Weinheim: Verlag Chemie.

FAO7 1977. China: Recycling of Organic Wastes in Agriculture (Report on an FAO/UNDP study tour to the Peoples' Republic of China, 28 April - 24 May 1977 (FAO Soils Bulletin 40) Rome: FAO.

Frossard, E., S. Sinaj, L-M Zhang, and ). L. Morel, 1996. "The Fate of Sludge Phosphorus in Soil-Plant Systems.' In Soil Science Society of America Journal, Vol. 60, No. 4, 1996.

Govilkar, Maltid, 1981. Key Note address: Why Study Biogas Technology?' In Seminar-Cum-Workshop on Janata Biogas Technology and Fodder Production. Karnal: NDRl.

Goswami, K.P., P.S. Bhorania and K. P. Patel, 1996. * Recovery of Water and Manure From Biogas Plant Slurry/ In Changing Villages, Vol. 15, Jan-Jun.

Gutterer, Bernard and Ludwig Sasse, 1993. 'Summary and Recommendations.' Report Biogas Survey 1992: Cross Section Analysis of Biogas Dissemination Programmes. Bremen, FRG: BORDA (Bremen Oversees Research and Development).

Havard-Ducfos, B., 1975. Las Plants Farrajeras Tropicales. Blume, Ed. Madrid.

Hisserich, H., 1947. " Le gaz de fumier an Ailemagne.' Land Wald und Garten, May 1947.

Horn, Thomas F., undated. ' Sludge Treatment- Soil Conditioning and Composting.' In Biogas Production and Utilization (ed. By Eiezabeth C. Price and et al.). Ann Arbor, Mich: Ann Arbor Science Publisher's Inc.

Hofman, G., 1988. ' Nitrogen Supply from Mineralization of Organic Matter/ In Biological Waste 26(1988).

Itrabansh, Shova, undated. Isolation of Different Types of Aerobic and Anaerobic Bacteria From Biogas Digester Under Laboratory Condition. Kathmandu: CEDA.

91

ICIMOD, 1991. 'Biogass and the Conservation of Energy through Improved Cooking-stoves in Nepal: Problems and Prospects/ In Report of the Seminar on Rural Energy and Related Technologies in Nepal. Kathmandu: ADB/n, ICIMOD, WECS.

lwabuchi, K. and T.Kimura, 1995. 'Aerobic Biodegradation of Dairy Cattle Faeces (Part 1). Heat Production Rate and Oxygen Uptake Rate/ In Waste and Organic Byproduct Processing Vol. 7, No.l. [Excerpted from Journal of the Japanese Society of Agricultural Machinery, 1994, 56(2).

Jarvenpaa, M and T. Maunu, 1995. 'The Economics of Energy Biomass Production on Set-Side Land/ In Waste and Organic Byproduct Processing Vol. 7, No.l. [Excerpted from Biomass tuotannon talous maatiloilla. Tyotehoseuran Julkaisuja, 1994, No. 333.]

Jiashi, Sun and Zhu Reng, 3 991. 'A Study on Applying "Biogas Fertilizer" to Prevent Plant Disease and Insect Pests/ In Biogas Forum, Vol. 2/ Special. [Excerpted from China Biogas, 8(4), 31-33, 1990, translated by Ren Shengquing]

Jiayu, Min and Li Zhengfang, 1991. 'A comparative Study on the Efficiencies of Fingerling Raising with Slurry from Biogas Disgester Chicken Manure and Mixed Baits/ In Biogas Forum Vol 2/ special. [Excerpted from China Biogas, 1990, 8( 1) 36-38, translated by Min Jiayu].

Kannaiyan, S., K. Ramasamy, K. Ilamurugu, and K. Kumar, 1992. Biological Nitrogen Fixation and Biogas Technology. Tamilnadu: Tamilnadu Agricultural University, India.

Karki, Amrit B. And Krishna M. Gautam, 1995. Effects of Slurry from Anaerobic Digestion of Organic Wastes on Crops and Vegetables and its Residua! Effect on Soil. Kathmandu.

Khanna S., Krishna Mohan (eds), . Wealth from Waste. New Delhi: TERI

Klein, C.A.M. de, R.S.D. van Logtestijn, H.G. van de Meer and J.H. Geurink, 1996. 'Nitrogen Losses due to Denitrification from Cattle Slurry Injected into Grassland Soil with and without a Nitrification inhibitor. In International Journal on Plant Soil Relationship.'

Lichtman, Rob, 1992. ' Diffusion or Confusion: Some Thoughts on 15 years of Biogas Programs/ m Biogas Forum Vol. II, No.49.

Lichtman, Rob, 1993. ' Confusion about Diffusion/ In Biogas Forum Vol. I, No.52.

Mahadevaswamy M. And L.V. Venkataraman, 1990. 'Integrated Utilization of Fruit-Processing Wastes for Biogas and Fish Production/ In Biological Wastes 32 (1990) 243-251. England: Eisevier Science Publishers Ltd.

Mahapatra, Krishna, 1985. 'The Puri Nightsoil Biogas Plant: A Sociological Evaluation Through A Case Study/ In Changing Villages Vol. 7 No.6, Nov-Dec.

Marry, B., S. Recous, D. Darwis and D. Robin, 1996. l Interactions Between Decomposition of Plant Residues and Nitrogen Cycling in Soil/ In International Journal on Plant and Soil Relationship 181.

Mazumdar, N.B. and Yashwant Singh, 1986. 'Promotional Strategy on Biogas Programmes.' In Biogas from Human Waste (Workshop Report). New Delhi: CORT.

92

Meng Xun, Hu Daize, Yang Kejung and Ren Shengqing, 1991. 'Biogas and the Construction of Ecological Agriculture in China.' In Biogas Newsletter No. 36, April 1991. Kathmandu Nepal.

Mengei, K., 1996. 'Turnover of Organic Nitrogen in Soils and its Availability to Crops/ In International Journal on Plant and Soil Relationship 181. Dordrecht: Kluwer Academic Publishers, Netherland.

Moser, Mark A., 1996. Biogas Utilization, in Lusk, P., P. Sheeler, C. Rivard {eds.) , Deploying Anaerobic Digesters: Current Status and Future. Colorado: National Renewalbel Energy Laboratory.

Mosey, Frank E., 1996. ' Environmental Impacts of Anaerobic Digestion and the Use of Anaerobic Residues as Soil Amendment.' In Lusk, P., Wheeler P., Rivard c (eds.) Deploying Anaerobic Digesters: Current Status and Future. Colorado: National Renewable Energy Laboratory.

Pluschke, Peter, 1990. 'Contamination in Sewage Sludge and Bioslurry.' In Biogas Forum Vol. I/Special.

Pokharel, R.K. and R.P. Yadav, 1991. Application of Biogas Technology in Nepal: Problems and Prospects. Kathmandu: IC1MOD.

Polak, Hans, 1992. ' Confusion about Diffusion: Some Remarks on Rob Lichtman's article on 15 years of Biogas Programmes/ In Biogas Forum Vol.1., No51.

Pry, L.J., 1975. Practical Building of Methane Power Plants for Rural Energy Independence. Andover, Hampshire, UK Chapel River Press.

P., Venkata Ramaiah, Suresh Kumar M. and Gopikrishna T, 1994. 'Bio Village - A New Perspective for Rural Development.' In Changing Villages Vol. 13, No. 1.

Rawat, B.S., 3 981. 'Gobar Gas-Cum-Compost Plant and the Economics of its Outputs.' Seminar Com Workshop on Janata Biogas Technology and Fodder Production. Kamal: NDRI.

Rajabapaiah, P, S. Gayakumar and Amuiya K.N. Reddy, 1981. 'Biogas Electricity.' In Renewable Energy Sources for Fuels and Electricity. Washigton D.C.: Island Press, Lovelo, California.

Santhanakumar, G., G. Kanthaswamy and T. Muthumaneksha, 1993. 'Studies on the Residual Effect of Organic Manures and Inorganic Fertilizers on Blackgram.' In Biogas Slurry Utilsation. New Delhi:CORT.

Santhanakumar, G. And S. Mutharasan, 1993. ' Impact of Biogas Slurry and Inorganic Fertilizer on the Soil Microorganisms/ In Biogas Slurry Utilsation. New Delhi:CORT.

Sasse, Ludwig, 1993. ' Comparison of Utilising Biogas Plants by Farmers in India and Indonesia/ In Biogas Forum Vol. IV., No. 55, 1993.

Sasse, Ludwig, 1990. ' Evaluation of Biogas Programmes - Methodology and Criteria. In GATE 11, 15-3-6, 1990A

Sasse, Ludwig, 1989. ' Evaluation of Ecological Benefits. In Biogas Forum No. 37.

93

Saxena, K. K., K. Nath and S.K. Srivastava, 1989. 'The Effect of Using Dung from Cattle Fed High-> Law-or No-Concentrate Rations, on the Quality and Nutritive Value of Slurry from a. Biogas Plant.' In Biological Wastes 28 (1989) 73-79.

Schreier, H., P.B. Shah, and S. Brown, 1995. Challenges in Mountain Resource Management in Nepal: Process, Trends, and Dynamics in Middle Mountain Watersheds. Proceedings of a Workshop, April 10-20, 1995. Kathmandu: ICIMOD.

Schreier, H., P.B. Shah, LM. Lavkulich and S. Brown, 1994. Maintaining Soil Fertility Under Increasing Land Use Pressure in the Middle Mountains of Nepal.' In Soil Use and Management (1994) 10, No. 3, 137-142. Huddensfield England: CAB International (Published for the British Society of Soil Science).

Sharma, U.P., 1981. 'Complete Recycling of Cattle-Shed Wastes Through Biogas Plant.' Seminar Com Workshop on Janata Biogas Technology and Fodder Production. Kamal: NARI.

Sherchan, D.P. and G.B. Gurung, 1996. ' Effect of Five Years Continuous Application of Organic and Inorganic Fertilizers on Crop Yields and Physico-Chemical Properties of Soil Under Rainfed Zaize/Millet Cropping Pattern.' Draft Report Presented at the Summer Crops Workshop at the National Maize Research Programme, Pampur.

Sherchan, D.P. and G.B. Gurung, 1995. 'An Integrated Nutrient Management System for Sustaining Soil Fertility: Opportunities and Strategy for Soil Fertility Research in the Hills. 'In Challenges in Mountain Resource Management in Nepal: Process, Trends, and Dynamics in Middle Mountain Watersheds. Proceedings of a Workshop, April 10-20, 1995. Kathmandu: ICIMOD.

Shi zhengshan, Zhang Ping and Huang Changke Li Peiqian, 1992. ' Study on Prevention and Cure of Wheat Gibberella Disease with Biogas-Slurry. In Biogas Forum Vol (2) special. [Excerpted from China Biogas, 1991, 9 (1), 11 -14, translated by Zhang Mi.

Shroff, V.N., 1993. 'Organic Manures and Biofertilizers - Only Solution to Many Problems.' In Changing Village, July-Sept., 96.

Sihe, Jia, 3 991." Technology of Planting the Pond Lotus Roots with Digester Slurry.' In Biogas Forum, Vol.2/special. [Excerpted from China Biogas, 8(4), 37, 1990, translated by Song Yuhua].

Subedi, Kalidas, 1993. 'Results of Various Composting Experiments Carried Out at Lumle.' A Review Papaer No. 93/1. LARC.

Takahashi, Shigeru and S. Yamamuro, 1995. ' Quantification of Effect of Temperature and Air-Drying Treatment in Paddy Soils on Mineralization of Soil Organic Nitrogen.' In ]AEQ 29 (2).

van Nes, Wim J. .1996. 'Biogas Support Programme: Results in the Period July 1992-1995'. In Biogas and Natural Resource Management, Number 51

Whitmore, A.P. and J.J. Schroder, 1996. 'Modelling the Chang in Soil Organic C and N and the Mineralization of N from Soil in Response to Applications of Slurry Manure.' In International Journal on Plant and Soil 184:185-194. Kluwer Academic Publishers. Printed Dordrecht in the Netherlands.

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Wong, Mamie Lau, 187. 'Calculation of the Quantity of Input for Biogas Plants.' In Biogas Newsletter No. 25, Nov. 1987. Kathmandu.

Yu, Min Jia, 1992. 'The Development of Fish-Breeding with Bio-Manure in China.' In Biogas Forum Vol (2) special. [Excerpted from China Biogas, 1991, 9 (4), 1-4, translated by Zhang Mi.

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Prologue

The field of slurry utitilization is an important one if the perceived twin benefits of biogas technology is to be fully utilized. The theoretical and conceptual bases behind biogas and slurry promotion is essentially justified in view of the finite nature of commodities we use for both fuel and mineral fertilizer. In fact, biogas and bioslurry both have potentials to contribute in our contemporary strivings for a sustainable society.

Lack of comparative studies of the effects on crop production of bioslurry compost, fresh liquid slurry, sun-dried slurry and ordinary compost are lacking. Nutritional analysis and field results in many cases are of dubious value because of the absence of proper research designs. This situation can be cleared only with experimentations footed on rigorous scientific principles.

The newness of slurry research is evident from the fact that literature is full of idiosyncratic usage of the terms like these: "sludge', 'bioslurry', 'biogas slurry', 'biodigested slurry', 'sun dried slurry' 'wet slurry', 'effluent', 'slurry' 'biomanure' 'biosol' 'biol' ' digested slurry' ' biofertilizer 'sludge manure' 'residual manure', 'liquid manure', 'fresh slurry', 'digested residue', 'digested sludge' 1 organic manure', etc. To be sure these are all organic manures/fertilisers and also these are biofertilisers. But slurry by definition is the mixture of solids and liquids. And it remains slurry as long as this mixture maintains a fairly constant proportion of liquid and solid in an accepted range. But then the literature often use biogas 'slurry' in such a loose manner (without proper explanations) that often times it is ' slurry' even if t is sun-dried with a drastically reduced moisture content. As 1 slurry' in its literal meaning is different from (in terms of moisture, the chemical stages of nutrients and their availability to plant) say a sundried form ( some how moist and wet substance with charges in its physical and chemical/nutritional composition), loose and unqualified usage of the terminologies makes slurry research results ambiguous and vague. The literature frequently distinguishes the differential effects of this biproduct of biogas plants. Yet ' BDS' or ' plain slurry' or 'bioslurry' are used no matter whether they are completely dried powdery forms or in the form of pastes or a free flowing mixture. The matter is further compounded by the use of the term ' sludge'. The residue when slurry is dewatered is called sludge in many cases. In others, the sedimented (residual) portion of slurry is taken as sludge. There are no problems with these. Problem arises when sludge' most oftentimes is used, indiscriminately and interchangeably, for 'slurry' in research reports. Some conceptual definitions providing boundaries between the terms, between the lay usage and scientific definitions, are in the need in slurry research. The is how science advances-the clearing of the terminological jungle is an urgent task before conducting any fruitful research. The term ' fresh slurry' is also frequently used in the literature. There will be not much problem if ' fresh' is defined in terms of the time slurry is taken out from the digester. Problem arises when fresh slurry is also sometimes taken as filtered or dewatered solid biproduct and entered into the research protocols as ' fresh slurry.' In others, the terms ' liquid manure' ' liquid slurry' are also used without qualifying whether it is the slurry as it comes out from the digester or whether it is a deliberately diluted, liquidified material, or the liquid obtained from the dewatering process. Ambiguity of research result compounds when sometimes wet' or ' moist' is taken as ' liquid.'.

In the Indian literature the term 'demonstration' is overwhelmingly used since the inception of the large scale farmer participatory research in slurry utilisation in crop production in the Eighties. Traditional agricultural extension tells us that a demonstration is usually an educational method in which proven and credible technologies are demonstrated in farmer's field. It seems from the review that the technology is just emerging. Yet, terms such as 'testing' 'trials' and 'experiments', ' verification trials', etc., are seldomly used. Of course, there will be " demonstration effects' of those trials and experimentations. It is just that in the accepted conventional academic parlance these activities were not 'demonstrations' but "trials' and 'experimentations'.

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For any research agenda in the natural sciences (as against in the social sciences where the concepts and terminologies have ‘sensitizing’ responsibilities), it is as important aspect that terminological ambiguities be cleared before proceeding ti the research work and pubilishing the reports.