Geoderma 207–208 (2013) 205–211

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Agronomic application of food processing industrial sludge to improvesoil quality and crop productivity

Kalyani Mahapatra a,⁎, D.S. Ramteke b, L.J. Paliwal a, Narendra K. Naik c

a Department of Chemistry, RSTM Nagpur University, Nagpur, Indiab EIRA Division, NEERI, Nehru Marg, Nagpur 20, Indiac Department of Biotechnology, Rungta College of Science and Technology, Durg, Chhattisgarh, India

⁎ Corresponding author. Tel.: +91 9420250901; fax:E-mail addresses: mahapatrakalyanii@yahoo.co.in (K

ds_ramteke@neeri.res.in (D.S. Ramteke), ljpaliwal@yaho

0016-7061/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.geoderma.2013.05.014

a b s t r a c t

a r t i c l e i n f o

Article history:Received 18 April 2012Received in revised form 3 May 2013Accepted 16 May 2013Available online 13 June 2013

Keywords:Crop productivityEnvironmentLand applicationPlant nutrientsSludgeSoil

Sludge, a by-product of wastewater treatment processes, is an alternative to conventional means of disposal andincreasingly applied to agricultural lands as a source of fertilizer. In the presentwork, sludge generated from foodprocessing industry was applied to agricultural soil as a conditioner and its effect on physio-chemical propertiesof the soil and crop productivity were studied. The industrial sludge was amended in different proportion(10–50 t/ha) with soil and the feasibility of these amendments were studied. The results revealed that applica-tion of sludge to soil increased its pH, EC, CEC and other nutrients such as organic matter and phosphorous. A re-duction in the soil nutrients (nitrogen and potassium) in post-harvest soil indicates their uptake from soil by theplant and thus, productivity increases. No indication/evidence of harmful effects of heavy metals from sludgeon quality of soil and cultivated product was found, when the amendment was controlled within the range of50 t/ha for both dry and wet sludge applied. However, deterioration in the growth rate was observed beyond30 t/ha amendment due to the excess organic and nutrient load accumulated in the soil. The effect of bio-fertilizer and chemical fertilizer to support the crop productivity were also studied. Thus, food processing indus-trial sludge application positively affects crop productivity and significantly improves soil quality. Still,much is tobe learnt from this study and the present investigation needs to be continued to determine whether the agricul-tural objectives are satisfied in longer term.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Sludge treatment or its disposal is the major problem of wastewa-ter treatment plant if it is not utilized as a fertilizer or for some othereconomical purpose. Sludge contains essential plant nutrients and or-ganic matter that can help/enhance crop production. Therefore, landapplication of sludge not only reduces its disposal costs but also pro-duce an alternative to landfill disposal or incineration which is morebeneficial and environment friendly. The agricultural use of sludgeprimed this salvaged material valuable and provides enough profitto defray other treatment costs. The present paper aimed to work inthis context and optimized the quantity of sludge to be applied on ag-ricultural land that would not harm soil quality and crop productivity.

Although the agricultural application of sewage sludge has becomean alternative to common waste treatment due to practical and eco-nomic reasons, a relatively high concentration of heavy metals presentin sewage sludge generated from the dense urban and industrial areaspose a threat to environment (Selivanovskaya and Latypova, 2003;

+91 712 2249752.. Mahapatra),o.co.uk (L.J. Paliwal).

rights reserved.

Singh et al., 2004;Wong et al., 2007). Sewage sludge application alwaysposes a risk to the environment resulting from nutrient imbalances andtoxic element accumulation and leaching. Metal transfer from sewagesludge to soil and subsequently, to groundwater and plants representspotential health and environmental risks (Bhogal et al., 2003; McBrideet al., 1997). Evidences for metal percolation have been reported in nu-merous long-term sludge application experiments (Streck and Richter,1997). Accumulation of heavy metal in soil can result in a loss of soilfunctions that may raise concerns about environmental quality protec-tion,maintenance of human health and productivity. Soil pollutionmayhave implications in phytotoxicity at high concentrations and result inthe transfer of heavy metals to the human diet from crop uptake orsoil ingestion by grazing livestock (Kabata-Pendias and Mukherjee,2007; Kabata-Pendias and Pendias, 2001; Nicholson et al., 2003).Based on the available evidences regarding various aspects of sewagesludge application on soil fertility and consequent effects on plant pro-ductivity, the possibility of its utilization for agronomy and horticulturewere reviewed by some researchers (Singh and Agrawal, 2008; Singh etal., 2011). According to them land application of sewage sludge is one ofthe important alternatives for its disposal. Being rich in organic and in-organic plant nutrients, sewage sludgemay be a substitute for fertilizer,but presence of potential toxic metals often restricts its uses.

206 K. Mahapatra et al. / Geoderma 207–208 (2013) 205–211

Many researches support and establish the positive effects ofsewage sludge amendment on crop yield and on physio-chemicalproperties of soil. For instance, Sigua et al., 2005a, 2005b stated thatrepeated applications of sewage sludge indicate no harmful effectson soil quality and forage quality. Their results show that repeatedland application of sewage sludge would not increase soil sorptionfor nutrients and trace metals. They suggested that successive landuse of sewage sludge for at least three years followed by no sewagesludge use for at least two years may be a good practice because itwill boost and/or maintain sustainable forage productivity and atthe same time minimize probable accumulation of nutrients, espe-cially trace metals. They advised that possibilities for economicallysound application strategies are encouraging, but more research is re-quired to find optimal timing and rates that minimizes negative im-pacts of sludge on environment, particularly on soil quality. Min etal., 2011 applied Anaerobically Digested Slurry (ADS) to soil to evalu-ate its effects in mitigating crop damage from parasitic Nematodes.They suggested that application of ADS might be feasible for mitigat-ing Nematode damage, but the rate and timing should be consideredcorrectly to determine the best application method. Müller da Silvaet al., 2011 assessed the effects of dry and wet sewage sludge on thegrowth and nutrient cycling of Eucalyptus grandis plantations inBrazil. They recommended that sewage sludge application positivelyaffect leaf litter production and significantly increase nutrient transferamong the components of the ecosystem.

Based on the above mentioned information on land application ofsludge as a fertilizer, pot culture experiments were conducted usingTrigonella foenum graecum (Fenugreek) plant to find the impact offood processing industrial sludge on soil properties and crop produc-tivity. The industrial sludge (both dry and wet sludge) were amendedin different proportion (10–50 t/ha) with soil and the feasibility ofthese amendments was studied. The quantity of sludge required toget better productivity was optimized without much change in theproperties of post-harvest soil. To support the crop production,biofertilizer and chemical fertilizer were also applied and their im-pacts were studied.

2. Materials and methods

2.1. Materials

Sludge samples (dry and wet) were collected from wastewatertreatment plant, Haldiram food processing industry, Nagpur, India.It is one of the largest sweets and snacks manufacturing industry inIndia where a number of food products were processed viz. frozenfoods, namkeens, sweets, cookies, papads, chips, packaged dry fruits,bhujia, dal mixtures etc. Wet sludge sample was collected directlyfrom digester after discharge and the dry sludge was collected fromthe industrial sludge bed after drying. All the chemicals used for prep-aration of reagents were of analytical grades and purchased fromMerck Pvt. limited, India. All the glassware were washed with soap,rinsed with nitric acid and then washed with deionized water beforeuse. Deionized water was used to prepare all required solutions.

2.2. Experimental design

Two sets of experimental treatments were conducted separatelyfor each, dry sludge and wet sludge. Each set of treatment containedeight pot culture experiments including control for the germinationof crop (Trigonella foenum graecum) under various soil and sludgecompositions. Clay pots, having capacity of approx. 15 l and diameterof 9 in. were taken. Each pot was filled with 5 kg of soil–sludgemixture containing differed amount of sludge viz. 10 t/ha, 20 t/ha,30 t/ha, 40 t/ha, and 50 t/ha. To check any additional requirementof fertilizer, two pots with 5 kg of soil–sludge mixture containing30 t/ha of sludge in each pot, were supplemented by biofertilizer

(Azotobacter) in one and chemical fertilizer (Urea) in other pot. Thefertilizers were supplied to soil in the form of blended seeds beforesowing them in two different pots. Hence, total sixteen pot cultureexperiments were conducted.

All the 16 pots were conditioned for 3–4 days before sowing ofseeds. Equal numbers of Fenugreek seeds were sown in all the potsat a particular distance apart. Each plant was irrigated with distilledwater and maintained under unsaturated conditions (moisture con-tent equivalent to 70%) to avoid the possible lixiviation of metalsand salt. The experiment was conducted in a greenhouse to avoidany contamination and infection to the crop during the germinationperiod. The temperature was maintained between 20 °C and 25 °Cthroughout the growth period. Lighting in the greenhouse was natu-ral. The experiment lasted for 15 days. In this experimental period,the plants developed completely and the effects of sludge werevisible.

2.3. Soil characterization

Soil samples were characterized before and after the experiment.At the end of the experiment, soil sample from each pot was takenand air dried, crushed, and passed through a 2 mm sieve. Metals con-tent of soil was extracted after digestion with 3:1 (v/v) concentratedHCl\HNO3 following 3051a method (USEPA, 1997b) and measuredby Atomic Absorption spectrophotometer (AAS) Perkin Elmer withgraphite furnace. The pH and electrical conductivity (EC) were deter-mined in saturation extract; pH was measured by a Crison micro-pH2000 (Thomas, 1996) and EC with a Crison 222 conductivity meter(Rhoades, 1996). Organic carbon (OC) content was determined bythe Walkley–Black method (Nelson and Sommers, 1996). N contentwas analyzed by the Kjeldahl method (Bremner, 1996) and phosphorus(P) according to Watanabe and Olsen (1965). Soil Cation ExchangeCapacity (CEC) was determined with NH4OAc/HOAc pH 7.0 (Sumnerand Miller, 1996). Soil cations (Ca2+, Mg2+, Na+ and K+) movedwith NH4OAc/HOAc pH 7.0 were measured by Perkin–Elmer 2280atomic absorption spectrophotometer. Soil texture was determinedaccording to Bouyoucos (1962).

2.4. Sludge characterization

Sludge samples were air-dried and crushed to pass a 2 mm sieve.A fraction of sample was crushed to pass through a 0.074 mm sieve.This fraction was used to determine organic carbon (OC), N andtotal metal content. EC and pH were determined in saturation extract.Organic carbon (OC) was analyzed byWalkley–Black method (Nelsonand Sommers, 1996). N was determined by the Kjeldahl method(Bremner, 1996) and phosphorus (P) according to Watanabe andOlsen (1965). Total metal content of sludge were determined by3051a method (USEPA, 1997b) and measured by Atomic Absorptionspectrophotometer (AAS) Perkin Elmer with graphite furnace. Sludge'sCation Exchange Capacity (CEC) was determined with NH4OAc/HOAcpH 7.0 (Sumner and Miller, 1996). Sludge cations (Ca2+, Mg2+,Na+ and K+) moved with NH4OAc/HOAc pH 7.0 were measured byPerkin–Elmer 2280 Atomic Absorption Spectrophotometer.

2.5. Plants analysis

At the end of the experiment, samples of plants were washedusing deionized water, dried at 80 ° C for 48 h, finely ground andstored at 5 °C until metals analysis. Cr, Ni, Cu, Zn, Cd, Co, Fe, Mn andPb concentrations were assessed by Perkin–Elmer 2280 Atomic Ab-sorption Spectrophotometer after dried tissues were digested in nitricacid and sulphuric acid following the standard procedure describedby Gerard et al., 2000.

Table 1Physio-chemical analysis of soil and sludge prior to experiment.

Properties Soil characterization Sludge characterization

Dry sludge Wet sludge

Textural analysisSand (%) 5.54 – –

Silt (%) 35.66 – –

Clay (%) 58.80 – –

Physical characteristicsBulk density (gm cm−3) 1.33 0.77 0.12Porosity % 67.37 76.67 77.48Water holding capacity % 48.03 98.54 94.94

Chemical characteristicpH (1:2.5) 7.55 6.71 6.58EC (1:2.5)(MScm−1, 25 ° C) 0.37 6.80 4.05Ca (meq l−1) 0.78 0.42 0.60Mg (meq l−1) 1.62 1.62 0.80Na (meq l−1) 6.15 93.65 28.52K (meq l−1) 1.48 45.74 43.58

Cation Exchange Capacity (CEC)Ca++

C mol(p+)kg−144.80 50 45

Mg++

C mol(p+)kg−142.20 67 72

Na+C mol(p+)kg−1

0.06 7.34 0.23

K+

C mol(p+)kg−10.03 0.67 0.58

CECC mol(p+)kg−1

73.63 1270 1644

ESP% 0.09 0.58 0.02

Fertility statusOrganic carbon % 0.51 12.38 14.33N Kg ha−1 1264.40 3075.06 3069.51P2O5 Kg ha−1 30.36 71.45 59.01K2O Kg ha−1 76.86 106.86 176.89

Heavy metalsCd mg kg−1 0.08 0.31 0.04Cr mg kg−1 0.01 4.27 0.34Co mg kg−1 0.01 6.09 0.21Cu mg kg−1 0.12 0.93 0.15Fe mg kg−1 48.70 642.70 19.10Mn mg kg−1 2.73 27.30 2.54Ni mg kg−1 0.01 1.60 0.06Pb mg kg−1 0.02 5.25 0.59Zn mg kg−1 4.78 2.07 0.52

207K. Mahapatra et al. / Geoderma 207–208 (2013) 205–211

3. Results and discussion

3.1. Properties of experimental soil and sludge

The physical analysis of the experimental soil indicated that soiltexture is clay with 5.54% sand, 35.66% silt and 58.80% clay. Table 1shows the result of soil and sludge analysis prior to experiment. Thetable also illustrate that sludge contained high nutrient load such asnitrogen ranged from 3069.5 to 3075.1 kg/ha, phosphorous and

Table 2Growth pattern of Fenugreek plant grown in soil amended by dry sludge.

Dry sludge amendment Sowing day Germination day Grow

Dry sludge control 18-08-2010 20-08-2010 3.7Dry sludge 10 t/ha 18-08-2010 20-08-2010 3.8Dry sludge 20 t/ha 18-08-2010 20-08-2010 3.8Dry sludge 30 t/ha 18-08-2010 20-08-2010 3.9Dry sludge 40 t/ha 18-08-2010 20-08-2010 3.5Dry sludge 50 t/ha 18-08-2010 21-08-2010 3.1Dry sludge 30 t/ha with Biofertilizer 18-08-2010 19-08-2010 4.0Dry sludge 30 t/ha with Chemical fertilizer 18-08-2010 21-08-2010 3.6

organic carbon with high mineral content like sodium, potassium,calcium and magnesium. However, the heavy metals concentrationhas been found under admissible limits (USEPA, 1997a). Since, theamount of required nutrients varies from crop to crop and differsfor type of soil, direct application of food processing industrial sludge(with high load of minerals, organics and nutrients) to agriculturalland may cause deterioration of the soil texture, and in turn, the pro-ductivity. Therefore, it was decided to optimize the quantity of sludge(both dry and wet sludge) to be added in agricultural land. This wasperformed by making different soil–sludge composition containingvariable amount of sludge from 10 to 50 t/ha of soil. The feasibilityof these amendments was studied and the quantity of sludge requiredto get better productivity without much change in the properties ofpost-harvest soil was optimized.

3.2. Effect of sludge amendment on plant growth

Many studies have been reported showing enhancement in cropyield after sludge application to agricultural land. This is because ofthe presence of macro and micronutrients present in sludge (Arslanet al., 2007; Barriquelo et al., 2003; Berti and Jacobs, 1996). Similar re-sults were obtained in the present work. The entire sequence ofgrowth rate and the variations are shown in Table 2 for dry sludgeand Table 3 for wet sludge amendments. It results revealed a measur-able increase in growth rate during the germination period i.e. from0 days to 15 days for all the applied amendments. Up to 30 t/haamendment, a linear increase in growth rate was detected as com-pared to control. Beyond that, growth rate was deteriorated due tothe excess organic and nutrient load accumulated in the soil throughsludge. It was also found that plant growth was much better in thepot filled by dry sludge–soil mixture as compared to wet sludgemixed to soil. The growth rate was hampered in the pot where chem-ical fertilizer was applied with 30 t/ha soil–sludge composition. Max-imum sequential growth of Fenugreek was found in the pot wherebiofertilizer was added with 30 t/ha soil–sludge mixture. Howeverit was not remarkable because addition of biofertilizer makes theamendment expensive. Thus 30 t/ha dry sludge mixed in soil wasfound to be optimum for plant growth.

After harvesting, the plant grown in 30 t/ha dry sludge amend-ment was further analyzed for its nutrient properties (N, P and K)and heavy metal concentration. The result indicated a considerableuptake of nutrients by the plant as compared to control. However,not much change was observed in the concentration level of heavymetals in plant except iron (Table 4). This indicates that the crop cul-tivated on sludge amended soil (containing up to 30 t/ha dry sludge)will not make any harmful effect after its consumption.

3.3. Effect of sludge amendment on physio-chemical properties of soil

The high concentration of nutrients, useful for plant, present insludge is the reason of its agricultural application (Dolgen et al., 2007;Kidd et al., 2007; Stacey et al., 2001). Many research have supportedand established the beneficial effects of sewage sludge amendment on

th after 5 days (cm) Growth after 10 days (cm) Growth after 15 days (cm)

5.2 7.35.4 7.55.5 7.95.3 7.75.0 7.74.9 7.36.0 7.95.2 7.4

Table 3Growth pattern of Fenugreek plant grown in soil amended by wet sludge.

Wet sludge amendment Sowing day Germination day Growth after 5 days (cm.) Growth after 10 days (cm) Growth after 15 days (cm)

Wet sludge control 18-08-2010 20-08-2010 2.6 4.9 7.1Wet sludge 10 t/ha 18-08-2010 20-08-2010 2.7 4.9 6.9Wet sludge 20 t/ha 18-08-2010 20-08-2010 3.0 5.1 7.0Wet sludge 30 t/ha 18-08-2010 20-08-2010 2.7 4.9 7.3Wet sludge 40 t/ha 18-08-2010 20-08-2010 2.6 4.8 6.5Wet sludge 50 t/ha 18-08-2010 21-08-2010 2.5 4.4 6.6Wet sludge 30 t/ha with Biofertilizer 18-08-2010 19-08-2010 3.6 5.1 7.6Wet sludge 30 t/ha with chemical fertilizer 18-08-2010 20-08-2010 3.0 4.9 7.3

208 K. Mahapatra et al. / Geoderma 207–208 (2013) 205–211

crop yield and physio-chemical properties of soil such as improved soilstructure, increased soil moisture and porosity, provision of plant nutri-ents, increased humus content, cation exchange capacity (Barzegar etal., 2002; Speir et al., 2003) and enhanced soil biological activity(Saviozzi et al., 1999).

In the present work the physio-chemical analysis of different soil–sludge composition was performed after crop harvesting. The specificparameters analyzed were: soil pH, EC, ESP, OC; available nitrogen,phosphorus and potassium. The variations in different parameterswith respect to different amendments for both dry and wet sludgeare discussed below.

3.3.1. Effect of sludge amendment on soil pHSoil pH, is one of the most informative and commonly measured

chemical properties of soil which directly influences plant growth. Itis a major factor affecting the availability of elements to plants. Inacidic soil, phytotoxic elements are more likely available which candamage the plant cells of the crop. As soil pH increases, availabilityof these toxic elements becomes lesser (except selenium and molyb-denum whose availability increases with pH). In order to ensure thatplants are not getting adversely affected by phytotoxic metals, highersoil pH needs to be maintained. It is, therefore, advised that sewagesludge must not be applied to land with a pH less than 5.0.

In the present work, the pH of the food processing industrialsludge applied to land was feasible for plant growth and it is in therange of 6.58 to 6.71. Sludge application increases the pH of the soilfor all the amendments from 10 t/ha to 50 t/ha as compared tocontrol. This is due to the dissolution of sodium, potassium and alka-line metals present in sludge. Results are presented in Fig. 1. Similarresults were obtained by other researchers and they also noticed anincrease in soil pH after sludge application to land (Cavallaro et al.,1993; Rato Nunes et al., 2008a, 2008b; Zhang et al., 2004). Workingon acidic soils, Mokolabate and Haynes, 2002 found that addition oforganic residues increased the pH of the soil. The response had directrelationship with the pH of the added organic materials.

3.3.2. Effect of sludge amendment on electrical conductivity (EC) of soilSoil Electrical Conductivity (EC) is a chemical property of Soil

which directly affects crop productivity. All the major and minor

Table 4Comparison of heavy metal and nutrient uptake by plant grown in normal soil (control) an

Heavy metal content Cdmg kg−1

Crmg kg−1

Comg kg−1

Cumg kg−1

Control ND ND ND NDFenugreek ND ND ND ND

Nutrient content Total N %

Control 5.59Fenugreek 6.50

ND—Not detected.

nutrients, essential for plant growth, are absorbed by the plant as cat-ions or anions. These ions, which are dissolved in the soil water, carryelectrical charge and represent the EC level of soil. Thus, EC level ofsoil indicates how many nutrients are available to crops to imbibefor better yield. Soil EC is also related to specific soil properties thataffect crop yield, such as topsoil depth, pH, salt concentrations andwater-holding capacity.

In the present experiment, amendment of sludge to soil raised itselectrical conductivity with respect to increasing sludge concentra-tion from 10 t/ha to 50 t/ha as compared to control. This was agood indication of nutrient availability to plant. The reason behind in-crease of EC level of soil was the rise in soil minerals coming fromsludge. It was also evident from the elevation in concentration levelof calcium, magnesium, sodium and potassium after application ofsludge to soil. The results are depicted in Fig. 2. Analogous resultswere obtained by Stamatiadis et al. (1999) and Ahmed et al. (2010)after application of sewage sludge to soil and sandy soil. Accordingto Richards (1954) soil EC 4.0 dSm−1 at 25 °C is the boundary be-tween normal and saline soils. Over and above this value, yields ofmany crops get restricted. In this work, the EC of untreated soil(control) was 0.37 dSm−1 which increases to 1.64 dSm−1 in case ofdry sludge and 0.48 dSm−1 for wet sludge amendment (50 t/ha),showing is a good indication of soil productivity.

3.3.3. Effect of sludge amendment on soil organic carbon (OC)Organic carbon of the soil is directly related to soil fertility and po-

tential of agricultural productivity. High organic matter content helpsin improving the physical and chemical properties of sandy (desert)soil (Garcia-Gil et al., 2004; Veeresh et al., 2003). In most of the agri-cultural soils, organic matter is increased by leaving residue on thesoil surface, rotating crops with grass or perennials, incorporatingcover crops into the cropping rotation, or by adding organic residuessuch as animal manure, synthetic fertilizer or sewage sludge.

In the present experiment, organic carbon raised in all the amend-ments with increasing sludge dose from 10 t/ha to 50 t/ha as comparedto control (Fig. 3). These results are similar to the observations found byother researchers, who noticed an increase in soil organic carbon aftersludge amendment (O'Brien et al., 2002; Zhang et al., 2004). Generally,the sludge application to farming land leads to an increase in its organic

d 30 t/ha sludge amended soil (dry sludge).

Femg kg−1

Mnmg kg−1

Nimg kg−1

Pbmg kg−1

Znmg kg−1

0.07 0.04 ND ND 0.060.16 0.12 ND ND 0.08

Total P (mg g−1) Total K (mg g−1)

8.93 6.239.04 6.90

6.6

6.8

7

7.2

7.4

7.6

7.8

8

Control 10 20 30 40 50 30 withbio

30 withchem

Soil

pH

Concentration of sludge (t/ha)

Wet Sludge

Dry Sludge

Fig. 1. Variation in post-harvest soil pH amended by different proportions of sludge.

0

1

2

3

4

5

6

7

Control 10 20 30 40 50 30 withbio

30 withchem

Soil

Org

anic

Car

bon

%ag

e

Concentration of sludge (t/ha)

Wet Sludge

Dry Sludge

Fig. 3. Variation in post-harvest soil OC %age amended by different proportions ofsludge.

209K. Mahapatra et al. / Geoderma 207–208 (2013) 205–211

carbon (Rato Nunes et al., 2008a, 2008b) owing to contribution of stableand soluble OM, both characterized by increase of soil microbial miner-alization (Gagnon et al., 2001). Gallardo et al. (2009a) observed anincrease in soil Organic matter after sludge application (30 t/ha) to ag-ricultural land, elucidating the favorable impact of sludge on soil micro-bial activity.

3.3.4. Effect of sludge amendment on exchangeable sodium percentage(ESP) of soil

ESP is a significant physio-chemical parameter of soil that directlyaffects soil productivity. It is a straight measure of sodium contentpresent in soil relative to other cations. When the exchangeable sodi-um percentage becomes high (exceeds 10–20% of exchange capacity),the pH value of such soil sample goes to above 8.5 and the soil showphysical conditions of low permeability, sticky when wet and hardwhen dry , nutritional disorders etc. which may be reflected as reduc-tion of crop growth and water logged conditions.

A regular increase in the soil ESP level was observed in both dryand wet sludge amendments with increasing the concentration ofsludge to soil from 10 t/ha to 50 t/ha (Fig. 4). The reason is the reten-tion of sodium content in soil from sludge which rises with increasingsludge dosage. Angin, and Yaganoglu, 2011 observed that sewagesludge application increased soil exchangeable sodium (Na) contentin all application rates. But, this increase does not make a differencefor agricultural productivity. However, it could be a problem inthe long-term usage because of its role in soil salinization ordeflocculation.

3.3.5. Effect of sludge amendment on cation exchange capacity (CEC)of soil

Clay particles and organic matter have negatively charged sitesthat hold positively charged ions on their surfaces. CEC describesthe ability of a soil to retain cations on soil colloids as a result of

0

0.5

1

1.5

2

2.5

Control 10 20 30 40 50 30 withbio

30 withchem

Soil

Ele

ctri

cal c

ondu

ctiv

ity

(m

scm

-1)

Concentration of sludge (t/ha)

Wet Sludge

Dry Sludge

Fig. 2. Variation in post-harvest soil electrical conductivity amended by differentproportions of sludge.

negative charges. CEC protects soluble cations from being leachedout of the plant root zone and therefore, is important for retaining nu-trients and making them available to plants. Two important elementsthat influences soil CEC are Soil organicmatter and clayminerals. An in-crease in soil organic matter through sludge may likely to increase soilCEC which can be defined as the number of cations adsorbed per unitweight of one hundred gram of dry soil.

Results of the current study indicated that CEC was significantlyhigher in the soil control as compared to experimental sludge–soilmixture (Fig. 5). This was expected that a large amendment of organ-ic matter would increase soil CEC, but it was not observed in the pres-ent study. Similar results were obtained by Sara Brallier et al., 1996.Liu and Haynes, (2010) observed that the long-term irrigation by ef-fluent with a high Na content will inevitably result in accumulation ofexchangeable Na in the soil. Although, in general, monovalent cationsare being held less strongly on cation exchange sites than divalentones, but by mass action the added Na displaces other cations(e.g. Ca and Mg) into soil solution that can be leached down thesoil profile, subsequently a decrease in soil CEC was observed. Thiscan also be explained by a decrease in exchangeable Ca and Mg insludge amended soil.

The above explanation is for the soil irrigated by wastewatercontaining high sodium content. Similar explanation can be used forthe present work. Since, the sludge applied to soil was of high sodiumcontent which increased soil ESP level regularly in both dry and wetsludge amendments with increasing the concentration of sludge tosoil from 10 t/ha to 50 t/ha. According to some researcher sampletreatment (i.e. air drying) may also be one reason that decreasesmeasured CEC (Bartlett and James, 1980; Menzies and Bell, 1988).

3.3.6. Effect of sludge amendment on nutrient parameters (N, P and K)of soil

Traditionally, Nitrogen (N) has been considered as one of the mostimportant nutrients for plants. It usually increases plant growth and

0

0.5

1

1.5

2

2.5

Control 10 20 30 40 50 30 withbio

30 withchem

Soil

ESP

%ag

e

Concentration of sludge (t/ha)

Wet Sludge

Dry Sludge

Fig. 4. Variation in post-harvest soil ESP %age amended by different proportionsof sludge.

0102030405060708090

100

Control 10 20 30 40 50 30 withbio

30 withchem

Soil

CE

C (

C m

ol(p

+)kg

-1)

Concentration of sludge (t/ha)

Wet Sludge

Dry Sludge

Fig. 5. Variation in post-harvest soil CEC amended by different proportions of sludge.

0

10

20

30

40

50

60

Control 10 20 30 40 50 30 withbio

30 withchem

Soil

anva

ilabl

e ph

osph

orus

as

P2O

5 (K

g /h

a)

Concentration of sludge (t/ha)

Wet Sludge

DrySludge

Fig. 7.Variation in post-harvest soil available phosphorus amended by different proportionsof sludge.

210 K. Mahapatra et al. / Geoderma 207–208 (2013) 205–211

crop yield. The application of sewage sludge to agricultural soils couldbe considered as an alternative to urea fertilization (Gasco et al.,2002) due to their high contents in organic matter and essential nu-trients such as nitrogen and phosphorus (Tsadillas et al., 1999). How-ever the application rates must be carefully calculated to avoid addingtoo much N, which may be leached out of the soil in the form of nitrateand degrades the environment. Increasing the application rate of sludgewill increase the available amounts of N and P (Oudeh, 2002).

Similar to CEC, the concentration of nitrogen and potassium wereconsiderably reduced in all the experimental amendments as com-pared to unamended soil. This is because of the utilization of thesenutrients by the crop and also by microbial activity. Comparable re-sults were obtained by Sigua et al., 2005a, 2005b. They observedthat the concentration of soil nitrogen declined by almost 50%suggesting that enrichment of nitrogen by using sewage sludge wasinsignificant. Likewise Mohammadi, 2010 found that the decrease insoil potassium may be due to K fixation by the hydroxides of Al andFe found in clay interlayers of soil. These hydroxides form insolublecompounds of potassium i.e. potassium aluminosilicates and conse-quently fix potassium (Malakouti and Afkhami, 1999).

Contrary to nitrogen and potassium, addition of sludge in the soilsincreased its Phosphorous content with increasing the amount ofsludge added to soil. Phosphorus is an essential plant nutrient, indis-pensable for phospholipids, ATP and nucleic acids synthesis and itsdeficiency can limit plant growth (Schachtman et al., 1998). Similarto the present work Ngole (2010) and Mohammadi (2010) observedan increase in soil phosphorous after sludge amendment. The varia-tions of N, P and K of post-harvest soil of the present experimentare depicted in Figs. 6, 7 and 8.

0

200

400

600

800

1000

1200

1400

Control 10 20 30 40 50 30 withbio

30 withchem

Soil

avai

labl

e ni

trog

en (

Kg/

ha)

Concentration of sludge (t/ha)

Wet Sludge

Dry Sludge

Fig. 6. Variation in post-harvest soil available nitrogen amended by different proportionsof sludge.

4. Conclusion

The aim of the research work was to find the feasibility of usingfood processing industrial sludge to soil that can substantiallyincrease its nutrient content, enhance crop growth and improvesoil properties. It was observed that besides the higher concentra-tion level of Organic Carbon, Nitrogen, Phosphorus, Potassium andother minerals in sludge, its application to soil was found suitablefor all the amendments applied i.e. from 10 t/ha to 50 t/ha forboth dry and wet sludge. However, deterioration in the growthrate was observed beyond 30 t/ha amendment because of the excessorganic and nutrient load accumulated in the soil through sludge. Areduction in crop productivity was also observed in the pots due tosimilar reason where chemical fertilizer was applied with 30 t/hasludge amendments. An increase in crop productivity was also ob-served with biofertilizer; though it was not very significant consideringcost effectiveness.

Considerable reductions in the nutrients (nitrogen and potassium)in post-harvest soil were observed which indicates their uptake fromsoil by the plant. An adequate increase in soil pH, EC, Organic carbonand CEC indicates improvement in soil properties that may enhancecrop production. The crop produced is not harmful to human beingsas there is no intake of heavy metals. Further, after harvesting, pro-ductivity of soil was found suitable for next cultivation. However,more work is needed to examine the actual effect of food processingindustrial sludge amendment to agricultural land since its influencecan only be observed after long term application.

0

10

20

30

40

50

60

70

80

90

Control 10 20 30 40 50 30 withbio

30 withchem

Soil

anva

ilabl

e po

tass

ium

as

K2O

(K

g/ha

)

Concentration of sludge (t/ha)

Wet Sludge

Dry Sludge

Fig. 8. Variation in post-harvest soil available potassium amended by different proportionsof sludge.

211K. Mahapatra et al. / Geoderma 207–208 (2013) 205–211

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