long-term effects of quality-compost treatment on soil

Plant and Soil 106, 253-261 (1988) �9 Kluwer Academic Publishers PLSO 7299

Long-term effects of quality-compost treatment on soil

A. MARCHESINI l, L. ALLIEVI 2, E. COMOTTI 2 and A. FERRARI 2 I Libero Docente of Agricultural Chemistry, Universith degli Studi di Milano, Milan, Italy and 2Dipartimento di Scienze e Tecnologie Alimentari e Microbiologiche, Universith degli Studi di Milano, Milan, Italy

Received 19 March 1987. Revised November 1987

Key words: compost treatment, crop production, Helianthus annuus L., mineral fertilization, pot-culture experiment, sandy soil, soil chemistry, soil microflora

Abstract The effects of the addition of compost, prepared from vegetable market refuse and stomach contents of

slaughtered cattle, were studied in a sandy soil contained in pots and kept in a greenhouse environment. Comparison was made between: i) a treatment involving pots containing compost mixed with 5% soil, ii) four treatments in which increasing quantities of compost homogeneously taken from the same lot (0, 10000, 20000, 30000 kg ha -l) were integrated with NPK mineral fertilizer to equalize available nutrients; iii) an untreated control. At 3, 4, and 5 years from the date of treatment, after various other crops, sunflower was planted. The yield obtained, though it fell off from year to year, was approximately double in the case of 95% compost. The other four treatments also resulted in production increases compared with the untreated control. Production was found to rise progressively with increasing quantities of compost. The improvement in soil chemistry and microbiology, as shown by analyses performed 5 years after treatment with compost, suggests that the rise in crop production may be attributed to an overall improvement in all components involved in the fertility of the soil used, in our experimental conditions.

Introduction

The possible benefits deriving from the addition of organic matter to agricultural land have long been known. However, to obtain optimal con- ditions, certain precautions need be taken. These mainly involve: a) a suitably balanced ratio bet- ween nutrients, b) the possible presence of toxic materials unaffected by biological degradation, in particular heavy metals, c) the possible presence of harmful microorganisms; d) a suitable degree of stabilization of the organic matter. An adequate choice of the material to be employed may suffice for the first two or three points, whereas a deter- minant factor for the last two is adequate treatment of the materials before use. An efficacious method for satisfying this requirement is that of compost- ing. This consists in the oxidation and maturation of the organic matter by microorganisms under

253

controlled conditions. It includes at least one stage in completely aerobic conditions and involves a temperature rise sufficient to destroy harmful or- ganisms.

Organic wastes of various origins can be added to the soil with the exclusive aim of eliminating refuse as well as that of exploiting this organic matter as a fertilizer. When harmful constituents are present and the aim is elimination of the refuse, the criteria involved may be either the limitation of the quantities applied, or application of the com- post on non-agricultural land. Only when the mat- erial available is of sufficiently high quality is it possible to apply optimal dosages to fertilize agri- cultural soils without risking phytotoxic effects or environmental pollution.

A number of investigators have studied the use of various types of compost, yet few have con- tinued their experiments for more than a few years

254 Marches in i et al.

after treatment. Studies have mainly involved solid urban waste with and without added sewage sludge. Composts from, for example, sewage sludge, various manures, straw and spend mushroom have also been studied. Little consideration has yet been given to better-quality composts deriving from selected urban refuse such as fruit and vegetable market waste, collective kitchen waste and waste from food industries. Crop production has been found to rise on addition of compost to cultivated land, with an effect at least comparable to that derived from the addition of more traditional or- ganic fertilizers such as animal manure. The in- crease in crop productivity, though less marked and less immediate than that obtained with the addition of mineral fertilizers, has been found to be longer-lasting, probably due to more progressive release of the nutrients. A further effect observed is a particular stimulation of root growth. The pos- itive effects of some composts have been found to diminish at higher dosages due to the onset of phytotoxic effects (Chu and Wong, 1984; Paris et al., 1982; Terman and Mays, 1973; Wang et al., 1984; Wong, 1985).

Studies have also been carried out to determine the effects of compost on the various components of soil fertility. Improved structural stability and porosity have been observed in treated soils, with a particular increase in the number of smaller pores (Guidi and Giacchetti, 1981; Guidi et al., 1980; Pera et al., 1983; Terman and Mays, 1973; Wang et al., 1984).

As regards the chemistry of compost-treated agricultural land, increases have been found for example in all pH, organic carbon and extractable phosphorus and potassium. These increases were time-progressive up to at least three years after treatment: this finding may be attributed to a gradual release of nutrients. The concentration of metallic contaminants also increased (Benedetti et al., 1981; Darmody et al., 1983; Paris et al., 1982; Terman and Mays, 1973).

The microbiology of treated soils has also been studied. Microflora is the third component of the natural fertility of a soil. The presence of a rich microflora is not only responsible for the biological cycles of the various elements, since they make nutrients available to the plants. Owing to phenomena of antagonism it also forms an active barrier against the proliferation of organisms

harmful to plants (Florenzano, 1972). The addition of compost to a soil, periodically or once only, results in a persistent increase in the counts of various groups of microorganisms, including the rhizosphere microflora. Stimulation has been found to affect not only total microflora globally (bacteria, also classifiable as oligotrophs, Acti- nomycetes, fungi) but also groups such as Azotobacter and proteolytic, ammonifying and cellulolytic microorganisms. Nitrifier response appears more variable, and differences have been found between ammonium and nitrite oxidizers. The beneficial effect on microflora was also con- firmed by the rise found in microbial activity (e.g., CO2 emission from soil) (Benedetti et al., 1981; De Bertoldi et al., 1981; Grappelli and Tomati, 1981; Mahmoud et al., 1984; Nishio and Kusano, 1980; Pera et al.,1983).

The aim of the research described here was to verify the eventual persistence of the positive effects at 3-5 years after treating a sandy soil contained in pots with various proportions of good-quality compost. In the first two years after treatment a rotation crop was grown (maize), followed by two successive rapid-cycle crops (chicory), with no fur- ther fertilization (yields not reported in this paper). In the next three years a cultivar of sunflower (Hel ianthus annuus L.) for cattle fodder was plan- ted. This plant is considered to exploit soil fertility particularly well (Girotto, 1975) and is thus well suited to evaluate any reduction in fertility or soil exhaustion phenomena due to intensive cultivation. The sunflower yield was determined for the third, fourth and fifth years, and in the fifth year chemical and microbiological soil analyses were carried out. A part of the research work was carried out near the Turin (Italy) branch (of which Professor Marchesini is director) of the Istituto Sperimentale per la Nutrizione delle Piante (experimental in- stitute for plant nutrition).

Materials and methods

E x p e r i m e n t a l condit ions

The experiments were carried out in the Mit- scherlich greenhouse at the Turin branch of the Istituto Sperimentale per la Nutrizione delle Piante. The greenhouse contained 22 trolleys, each carry-

ing 24 pots. Each pot contained approximately 8 kg of a sandy soil, the main features of which are reported in Table 1. The trolleys were taken out into the open air from April to October.

Regarding the climatic conditions during the three years when sunflower was cultivated, May was cool in 1984 and warm in 1986, whereas Sep- tember was milder in 1985 (monthly average tem- perature in May: 1984, 13.4~ 1985, 16.3~ 1986, 19.9~ in September: 1984, 18.3~ 1985, 21.6~ 1986, 19.0~

Fertilizing treatment

Treatments were carried out exclusively during the year 1981. The six types of treatment, each generally carried out on 4 trolleys (96 pots), were as follows: 0, no fertilizing treatment; M, mineral fertilization at a dosage equivalent to

190kgNha J of ammonium sulphate, 160kg Pha l perphosphate, and 180kgKha-I potassium sulphate;

CI, compost fertilization at a dosage equivalent to 10,000 kgha -t , with added mineral fertilizer;

C2, compost fertilization at a dosage equivalent to 20,000 kg ha -J , with added mineral fertilizer;

C3, compost fertilization at a dosage equivalent to 30,000 kg ha -J , with added mineral fertilizer;

CX, pots filled with compost mixed with approxi- mately 5% of soil to ensure a physical struc- ture suitable for plant growth. This treatment corresponds to the highest possible level of organic fertilization and was included to deter- mine the consumption of organic matter during the period involved. It obviously does not give a quantity of nutrients comparable to that present in the pots treated with mineral or

Table 1. Physical and chemical characteristics of the sandy soil used (values on dry matter)

pH 7.4 Texture

sand 85.3% silt 10.4% clay 4.3%

Organic C 1.11% Total N 0.11% C/N 10.1 Assimilable P (as P) 24.38 mg kg- Assimilable K (as K) 48.00 mg kg- l

Effects of compost treatment 255

mixed fertilizers. It was applied to only 2 trolleys (48 pots).

In CI, C2, and C3 the compost treatment was integrated with NPK mineral fertilizer to bring the total quantity of nutrients up to the same level as that achieved with treatment M, taking the annual nutrient utilization of the compost added to the soil to be equal to about one-third. This is in agreement with the percentages suggested for nitrogen with reference to animal manure (Paris et al., 1982). Given the type of matter of which it is composed, the compost used in these experiments may be considered comparable to manure from this point of view.

The raw material for the compost was refuse from the Turin General Market mixed with the stomach contents of slaughtered cattle (ratio about 9:1). Transformation was carried out in two stages: the first in a rotary digester and the second in periodically turned piles kept under cover at air temperature. The process was completed in ap- proximately five months. Table 2 reports some chemical and microbiological features of the com- post as it was applied, after six months' storage from the end of the composting process. This was felt to be a higher-quality compost than that ob- tained from solid urban refuse, since it was produced from selected agricultural waste.

Cultivation

After each crop the plants were removed and the soil in each pot was sieved to remove roots. Bet- ween crops, the soil was kept free of spontaneous vegetation. Crop water requirements were satisfied during sunflower cultivation (April-September) by sprinkler irrigation. Each pot received about 2 liters per day, which in the given experimental environ- ment was such as to permit optimal growth.

Determination of plant yield

This research takes into consideration only the sunflower crop yield in the years 1984, 1985, and 1986. The plants were cut at the root neck, and dry weight was determined after oven drying at 120~ Seed and stem weight were determined separately. The sum of these two parameters, indicated hereaf-

256 Marchesini et al.

Table 2. Chemical and microbiological characteristics of the compost used (values on dry matter)

Moisture 12.6% Total aerobic bacteria pH 7.4% Total anaerobic bacteria Organic matter 21.5 ~ % Fungi Organic C 11.6% Ammonifiers Total N 1.5% Aerobic N-fixing bacteria NH4-N 18 mg kg Aerobic cellulolytic bacteria NO 3-N 366 mg kg Anaerobic cellulolytic bacteria C/N 7.7 Escherichia cord Total P (as P) 0.33% Fecal streptococci Total K (as K) 0.4% Sulfite-reducing clostridia Total Ca 3.2% Salmonella Total Mg 0.7% Total Fe 2.0% total Cu 460 mg/kg

3.3 x 10S.g -t 3.9 x 107.g -t 5.0 x 106.g -I 6.5 x 107.g -1 not detectable 5.7 x 102.g -l not detectable 0.0g -I O.Og -l 3.3 X 106.g -I 0.0 (50 g)- t

a by combustion at 400~

ter as total dry matter, is used for brevity in the presentation of data. Analytical results were processed by three-way analysis of variance (treat- ment, year, crop parameter) and successively by Duncan's multiple-range test.

phosphorus, Olsen method; assimilable potassium, extraction with 1 N ammonium-acetate solution; CaCO3, CO 2 developed on attack by HC1. The same methods had been applied to analyze soil and compost before the experiments began, in 1981 (Tables 1 and 2).

Soil sampling

Samples of the vegetation-free soil contained in the greenhouse pots in Januyary 1986 were taken for chemical and microbiological analyses. Ali- quots were taken from various points in each pot and brought together to form a single sample from each trolley. The soil was allowed to dry in a dark dry place for one night, then sieved (2-mm mesh sieve) and placed in screw-top plastic containers which were stored in a cool environment (Pochon and Tardieux, 1962)

Chemical analysis

Analysis was performed on average samples for each treatment. The methods followed were those proposed by the Societ~ Italiana della Scienza del Suolo (1985).. The following is a summary. Dry matter, oven drying at 105~ for 18h; pH, with pH-meter using combined electrode on a suspen- sion of soil in distilled water 1:2.5; organic carbon, oxidation with potassium bichromate; organic matter, estimated by combustion at 400~ or cal- culated conventionally as organic carbon (organic C x 1.72); total nitrogen, Kjeldahl method; C/N ratio, organic carbon/total nitrogen; assimilable

Microbiological analysis

Each of the 22 samples was analyzed twice. Serial tenfold dilutions in quarter-strength Ringer's solu- tion (Harrigan and McCance, 1966) were prepared starting from a homogenized 1:10 suspension of the soil sample in a 0.1% Na-pyrophosphate/water solution (Pochon and Tardieux, 1962). Aliquots (1 ml) of the various dilutions were then inoculated either into liquid culture media contained in test tubes (multiple-tube technique for determination of the most probable number, MPN, using a triplicate set of test tubes) or, alternatively, into agarized media (triplicate set pour plates). Where required, anaerobic incubation was performed using the Gas-Pak System (BBL). The microbial groups de- termined, the media and the incubation conditions were: total aerobic bacteria, plate count agar (7 days at

28~ total anaerobic bacteria, Todd Hewitt

broth + 1.4% agar (10 days at 28~ in anaero- biosis);

fungi, malt agar with addition of rose bengal, 33 mg 1-l, and tetracycline, 100 mg 1-l (6 days at 28~

aerobic nitrogen-fixing bacteria (Azotobacter), liq-

uid medium (Pochon and Tardieux, 1962) (15 days at 28~ microscopic verification of the growth of Azotobacter;

anaerobic nitrogen-fixing bacteria, liquid medium (Augier, 1957) (30 days at 28~ in anaerobiosis), findings for gas production and rH reduction;

ammonifiers, asparagine liquid medium (Pochon and Tardieux, 1962) (15 days at 28~ amm- onium detection with Nessler reagent;

autotrophic nitrifiers, ammonium liquid medium (Pochon and Tardieux, 1962) (40 days at 28~ detection of nitrites and/or nitrates using diph- enylamine-H2 SO 4 reagent;

denitrifiers, soil extract liquid medium, incubation under helium + acetylene (90:10 v/v) in rubber- stopper sealed Pankhurst tubes (15 days at 28~ gas-chromatographic detection of N20 production (Allievi et al., 1987);

aerobic and anaerobic cellulolytic microorganisms, liquid media with filter-paper smear (Pochon and Tardieux, 1962) (20 days at 28~ for aerobes, 20 days at 33~ in anaerobiosis for anaerobes). The dry weight of soil samples was determined

by oven drying aliquots of the samples at 105~ The same methods had been used for microbiologi- cal analysis of the compost (Table 2). Findings for each microbial group were processed by two-way analysis of variance followed by Duncan's test.

Results

Crop yieM

Total yield fell steadily from year to year. When the yield of seed was considered separately, no progressive yearly decline was observed (Fig. 1). In all cases the maximum dose of compost CX produced substantial increases even after several years, with the yield being approximately doubled. All the other fertilizing treatments produced in- creases, although to a lesser degree. It was also possible to observe a progressive increase in yield corresponding to the amount of compost in the soil, at least for soils C2 adn C3. No statistically significant difference was found between C 1 and M, even though it would seem to appear, from the data reported in Fig. 1, that the only year showing no production difference was 1984, the closest to the fertilizing treatment.

Effects of compost treatment

Chemical analysis of soil

257

The outstanding finding was the persistently higher content of organic substances and markedly higher content of other important nutrients in the maximum-compost soil CX compared with all others (Fig. 2). It also appears likely that the treat- ment with organic matter succeeded in limiting the progressive alkalinization of the soil by irrigation with water rich in carbonates. No significant dif- ferences were found between the control soil, the mineral-treated soil and those treated with increas- ing quantities of compost C1, C2 and C3. Only the assimilable phosphorus showed a slight rise corres- ponding to increasing amounts of organic matter added to the pots (treatments C1, C2, C3).

Microbiological analysis of soil

For seven out of nine groups of heterotrophic microorganisms, the highest number was that cor- responding to maximum compost (CX), and in six cases this difference was found to be statistically significant (Fig. 3). The opposite was true when the group of autotrophic nitrifying bacteria was con- sidered, and the smallest number was found for the CX samples. Microbial counts in the other cases did not appear to be correlated with the treatments.

Discussion

In a stage preliminary to this investigation the compost employed had shown no phytotoxic eff- ects even at dosages equivalent to 60,000 kg ha -1 .

The sunflower crop yield at three, four and five years after fertilizing treatments with organic and mineral substances showed higher productivity and thus better fertility in the cases of the maximum- compost soil CX. One of the factors responsible for this was the NPK content, which in the samples taken before the final crop was growth--five years after treatment--was still higher in the CX soil than in the others and in the control. However, yield was found to fall progressively from year to year, as was also the case for the untreated soil and for those treated with mineral fertilizer or mineral/ compost mixtures. This is also indicative of a pro- gressive reduction in nutrient reserves. The fact

258 Marchesini et al.

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Fig. 1. Sunflower crop yields 3, 4 and 5 years after treatment, with results o f Duncan ' s test. Rectangles indicate statistical populations. Treatments: O = control; M = N P K mineral fertilizer only; C1, C2 and C3 = compost at 10000, 20000 and 30000 kg h a - t, integrated

with mineral NPK; CX = compost at 95% (see Methods).

that the production of seeds alone undergoes no progressive reduction may be attributed to the fluc- tuation of assimilable nitrogen due to climatic fac- tors. Such fluctuations do not always coincide with a plant's nutritional requirements during growth.

A maximal treatment with compost, such as that tested experimentally with treatment CX, is ob- viously far beyond the possibilities of actual ap- plication. Nonetheless, it was useful to highlight all effects taking place on the chemical and micro- biological features of the soil and on the crop yield. In any case, it is possible to suppose the effect to be progressive, in proportion to the amount of com- post applied�9 This hypothesis appears to find some confirmation in the finding that the presence of quite low levels of compost in soils C1, C2 and C3 had a beneficial effect on yield even after some

years, at least in the case of the two higher dosages (20,000 and 30,000 kg ha- ~). Purely mineral fer- tilization, although in significant quantity, after a period of at least three years appeared to no longer have a significant effect on crop yield: in fact, the increase was limited.

The results of the chemical and microbiological analyses performed on the soil five years after treat- ment showed some correlations. The much larger amounts of organic matter still present in the max- imum-treatment soil CX were correlated with the larger numbers of heterotrophic microorganisms found. The latter, being able to mineralize such substances, make nutrients available to the plants. This finding, together with the greater availability of assimilable phosphorus and potassium, is indica- tive of a general improvement in the chemical and

Effects of compost treatment 259

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Fig. 2. Results of chemical analysis of soil 5 years after t reatment (values on dry matter). Treatments: O = control; M = N P K mineral fertilizer only; e l , C2 and ( 3 = compost at 10000, 20000 and 30000kgha -1 , integrated with mineral NPK; CX = compost at 95% (see Methods).

microbiological status of the substrate on.which the plant grows, and may suffice to explain the con- siderable increase in yield.

The smaller quantity of autotrophic nitrifying bacteria (ammonium oxidizers) in pots containing larger quantities of organic matter (CX treatment) does not necessarily point to a direct inhibition of autotrophs by the organic matter. Some authors have even found a stimulating effect on autotrophic nitrite oxidizers (De Bertoldi et al., 1981; Pera et al., 1983). In any case, the presence of fewer nitrifiers does not appear to have any harmful effects on our crops.

A further microbiological note involves the presence of mycorrhizal fungi in the root system of plants grown in pots containing compost (C 1, C2, c3, cx).

The chemical and microbiological situation was not generally such as to permit any clear dif- ferentiation between the untreated control and the intermediate treatments M, C1, C2 and C3, or to point to correlations between the chemical and

microbiological parameters considered and the dose of compost used in the various treatments. At least with regard to the microbiological analyses, the statistical variability due to the built-in limita- tions of the methods which could be used may have masked slight differences, despite the considerable number of determinations performed to limit this variability. On the other hand, the crop yields cor- related well with these treatments. On this basis, it may be suggested that the microflora of the soils treated with organic fertilizer, compared with that of those not so treated, consists of a qualitatively different population offering more beneficial con- ditions for plant growth and at the same time ex- cluding the development of harmful organisms. It appears possible to exclude the hypothesis of the fertilizing effect being exhausted after some years.

In conclusion, our experimental findings confirm that composting is not only a method for the eli- mination of organic waste, but is able to produce an agriculturally useful compost if suitable mat- erials are used. Its usefulness consists not so much

2 6 0 Marchesini e t al .

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Fig. 3. Results of microbiological analysis of the soil 5 years after treatment with results o f Duncan ' s test. Mean values increase from left to right; rectangles denote statistical populations. Treatments: O = control; M = N P K mineral fertilizer only; C1, C2 and C3 = compost at 10000, 20000 and 30000kgha - t , integrated with mineral NPK; CX = compost at 95% (see Methods).

in providing the plant with considerable quan- tities of immediately available nutrients, as in help- ing to maintain or re-integrate that long-term nat- ural fertility which involves the biological cycles of the elements in cultivated land, thus preventing its exhaustion. The favorable effects are still present even ater some years, the dosages need not necess- arily be high.

Acknowledgements

The authors would like to thank Mr Giovanni Chiesa, Director of Research for the Castagnetti, spa Company of Grugliasco (Turin, Italy) for his invaluable aid, Dr Maria Rita Allione (R and D Dept. Management) for help in statistical proces- sing of the data, and Dr Ninetta Siragusa of the Turin Istituto Sperimentale per la Nutrizione delle Piante for assistance in the collection of chemical data.

References

Allievi L, Catelani D, Ferrari A and Treccani V 1987 A method for counting denitrifiers by N20 detection. J. Microbiol. Methods 7, 67-72.

Augier J 1957 A propos de la fixation biologique de l'azote atmospherique et de la numeration des Clostridium fixateurs dans les sols. Ann. Inst. Pasteur 92, 817-824.

Benedetti A, Cavallari L and Nigro C 1981 On the humic balance of the soil. Note I. Effect of different organic mat- erials. Ann. Ist. Sper. Nutriz. Piante 1 l, 1 19.

Chu L M and Wong M H 1984 Application of refuse compost: yield and metal uptake of three different food crops. Con- servation Recycling 7, 221-234.

Darmody R G, Foss J E, Mc Intosh M and Wolf D C 1983 Municipal sewage sludge compost-amended soils: some spa- tiotemporal treatment effects. J. Environ. Qual. 12, 231-236.

De Bertoldi M, Giovannetti, Pera A and Vallini G 1981 Impatto con la microflora del suolo. In Utilizzazione dei Fanghi e Compost in Agricultura, Collana del Progetto Finalizzato

Effects of compost treatment 261

"Promozione della QualitY. del' Ambiente", C.N.R. AR/2/20- 27, Roma, p. 127.

Florenzano G 1972 Elementi di Microbiologia del Terreno. REDA, Roma, 445 p.

Girono G 1975 I1 Girasole. Edagricole, Bologna, 54 p. Grappelli A and Tomati U 1981 Effetti sulla rizosfera, sulla

microflora del terreno e sul biochimismo delle piante. In Utilizzazione dei Fanghi e Compost in Agricoltura, Collana del Progetto Finalizzato "Promozione della Qualitfi dell' Am- biente", C.N.R. AR/2/20-27, Roma, p. 159.

Guidi G and Giacchetti M 1981 Variazioni di alcune proprietfi fisiche e chimiche del terreno. In Utilizzazione dei Fanghi e Compost in Agricoltura, Collana edel Progetto Finalizzato "Promozione della Qualit~ dell' Ambiente", C.N.R. AR/2/ 20-27, Roma, p. 97.

Guida G, Petruzzelli G, Pagliai M, Giachetti M, Lubrano L and La Marca M 1980 Applicazione di fanghi e compost su una coltura di mais. L'Agricoltura Italiana 109, 63-73.

Harrigan W F and McCance M E 1966 Laboratory Methods in Microbiology. Academic Press, London and New York, 362 p.

Mahmoud S A Z, Abd-el-Nasser M, Safwat M S A and Fargha- ly M M 1984 Replacing organic matter in arid lands. BioCycle 25, 43~44.

Nishio M and Kusano S 1980 Fluctuation patterns of microbial numbers in soil applied with compost. Soil Sci. Plant Nutr. 26, 581-593.

Paris P, Gavazzi C and Robotti A 1982 Valutazioni agrono- miche di compost da rifiuti solidi urbani. Proceedings of the SEP Pollution 1982 Congress "Cittfi e Ambiente", Padova, April 18 22, p. 341.

Pera A, Vallini G, Sireno I, Bianchin M L and De Bertoldi M 1983 Effect of organic matter on Rhizosphere microorgan- isms and root development of Sorghum plants in two different soils. Plant and Soil 74, 3 18.

Pochon J and Tardieux P 1962 Techniques d'Analyse en Micro- biologic du Sol. Ed. De la Tourelle, StMand4-Paris, 111 p.

SocietY. Italiana della Scienza del Suolo 1985 Metodi Nor- malizzati di Analisi del Suolo. Edagricole, Bologna, 100 p.

Terman G L and Mays D A 1973 Utilization of municipal solid waste compost: research results at Muscle Shoals, Alabama. Compost Sci./Land Utiliz. 14, 18-21.

Wang S H, Lohr V I and Coffey D L 1984 Spent mushroom compost as a soil amendment for vegetables. J. Am. Soc. Hort. Sci. 109, 698-702.

Wong M H 1985 Effects of animal manure composts on tree (Acacia confusa) seedling growth. Agricultural Wastes 13, 261-272.