Waste Management 29 (2009) 2437–2445

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Waste Management

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Economical and environmental implications of solid waste compost applicationsto agricultural fields in Punjab, Pakistan

M. Akram Qazi a, M. Akram a, N. Ahmad b, Janick F. Artiola c, M. Tuller c,*

a Soil and Water Testing Laboratory, Thoker Niaz Baig, Lahore, Pakistanb Institute of Geology, University of the Punjab, Quaid-e-Azam Campus, P.O. Box 54590, Lahore, Pakistanc Department of Soil, Water and Environmental Science, The University of Arizona, P.O. Box 210038, Tucson, AZ 85721, United States

a r t i c l e i n f o a b s t r a c t

Article history:Accepted 4 May 2009Available online 5 June 2009

0956-053X/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.wasman.2009.05.006

Abbreviations: CC, ceiling concentrations; DAP, delectrical conductivity; EPA, US Environmental Protectsolid waste; MSWC, municipal solid waste compost;profit; PC, pollutant concentration; SOM, soil organicphosphorus; VCR, value-to-cost-ratio.

* Corresponding author. Tel.: +1 520 621 7225; faxE-mail address: mtuller@cals.arizona.edu (M. Tulle

Application of municipal solid waste compost (MSWC) to agricultural soils is becoming an increasinglyimportant global practice to enhance and sustain soil organic matter (SOM) and fertility levels. Potentialrisks associated with heavy metals and phosphorus accumulations in surface soils may be minimizedwith integrated nutrient management strategies that utilize MSWC together with mineral fertilizers.To explore the economic feasibility of MSWC applications, nutrient management plans were developedfor rice–wheat and cotton–wheat cropping systems within the Punjab region of Pakistan. Three-year fieldtrials were conducted to measure yields and to determine the economic benefits using three manage-ment strategies and two nutrient doses. Management strategies included the application of mineral fer-tilizers as the sole nutrient source and application of mineral fertilizers in combination with MSWC withand without pesticide/herbicide treatments. Fertilizer doses were either based on standard N, P and Krecommendations or on measured site-specific soil plant available phosphorus (PAP) levels. It was foundthat combining MSWC and mineral fertilizer applications based on site-specific PAP levels with the use ofpesticides and herbicides is an economically and environmentally viable management strategy. Resultsshow that incorporation of MSWC improved soil physical properties such as bulk density and penetrationresistance. The PAP levels in the surface layer increased by the end of the trials relative to the initial sta-tus. No potential risks of heavy metal (Zn, Cd, Cr, Pb and Ni) accumulation were observed. Treatmentscomprised of MSWC and mineral fertilizer adjusted to site-specific PAP levels and with common pestmanagement showed highest cumulative yields. A basic economic analysis revealed a significantly highercumulative net profit and value-to-cost ratio (VCR) for all site-specific doses.

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1. Introduction

The rice (Oryza sativa L.) – wheat (Triticum aestivum L.) and cot-ton (Gossypium hirsutum L.) – wheat cropping systems are amongthe largest agricultural production systems in the world (Ladhaet al., 2003). They cover an area of approximately 8.3 million hawithin the Punjab, a semi-arid to arid region in Pakistan with an-nual precipitation ranging from 55 to 247 mm (FAO, 2004). Cottonaccounts for about 8.2% of Pakistan’s agricultural production andcontributes about 3.2% to the gross domestic product (GDP).

Intensive farming operations, unbalanced application of chemi-cal fertilizers without prior analysis of soil nutrient status, inade-

ll rights reserved.

iammonium phosphate; EC,ion Agency; MSW, municipalOM, organic matter; NP, netmatter; PAP, plant available

: +1 520 621 1647.r).

quate land management and cultivation of high yielding cropvarieties have caused a significant decline in soil organic matter(SOM) and crop productivity over the last decades (Saha et al.,2007; Zia et al., 1998). SOM levels in soils under rice–wheat andcotton–wheat crops are categorized as poor to low (Nizami andKhan, 1989; Zia et al., 1998). In addition, traditional sources of soilorganic matter such as animal waste, crop residues and green man-ure are rapidly declining due to burning of waste and residues andutilization of straw as animal feed (Lal, 2005; Skoulou and Zabanio-tou, 2007; Tejada et al., 2008). While maintaining adequate SOMlevels is important for sustaining favorable physical growth condi-tions and fertility for crop production (Madrid et al., 2007), manyrural farming communities in the Punjab consider application ofgreen manure uneconomical and as a waste of land resources be-cause they do not see immediate cash returns (Akram et al., 2007).

An alternative source of organic matter is municipal solid wastecompost (MSWC). The application of MSWC to agricultural land isbecoming an increasingly important global practice to enhance andsustain soil organic matter status (Madrid et al., 2007; Weber et al.,2007) and crop production (Montemurro et al., 2007). In many

Table 1Soil physical and chemical properties at the beginning of the field trials.

Cropping system Rice–wheat Cotton–wheat

Physical soil propertiesSoil texture Loam Sandy loamSand content (%) 43.6 64.4Silt content (%) 37.2 21.2

2438 M.A. Qazi et al. / Waste Management 29 (2009) 2437–2445

countries, the application of composted MSW to agricultural fieldsis considered a low-cost alternative to open landfill disposal orincineration (Bruun et al., 2006). In Pakistan, large quantities ofMSW are currently deposited in unlined open landfills (PEPA,2005). This method of disposal is raising public health concernsdue to elevated risks for air pollution and contamination of potablewater (Woodbury, 1992). The potential marketability of MSWCgenerated substantial interest from private Pakistani enterprisessuch as Waste Busters. This company invested in composting facil-ities and community waste management projects in 1996, sellingMSWC to farming communities in the Punjab region. Reuse ofcomposted MSW can reduce open landfill disposal and associatedenvironmental impacts (Noble and Coventry, 2005). In addition,MSWC applied to agricultural soils provides excellent means tosupply organic matter and improve nutrient status (Jilani, 2007)and physical properties (Annabi et al., 2007; Weber et al., 2007).However, there is justified concern regarding potential accumula-tion of heavy metals in surface soils from composted MSW (Madridet al., 2007; Weber et al., 2007), including the possible migration oftoxic metals into the food chain (During and Gath, 2002).

Municipal solid waste composts are considered low-nutrientfertilizers with a plant available nitrogen/phosphorus (N/P) ratioof approximately 1:2 (Spargo et al., 2006). In contrast, optimal soilN/P ratios for most crops range between 7:1 and 10:1 (Heckmanet al., 2003; Sikora and Enkiri, 2004). Applications based on nitro-gen demand only, can require MSWC rates close to 100 tons per ha,leading to N/P imbalance and phosphorus accumulation close tothe soil surface. Elevated soil P levels can be problematic fromenvironmental point of view, as colloid facilitated transport withsurface runoff leads to phosphorus loading of surface water bodiesand associated risks of eutrophication (Eghball, 2002; Kundu et al.,2007). To avoid excessive phosphorus loadings, Juang et al. (2002)and Singer et al. (2004) emphasize the need for phosphorus –rather than nitrogen-based compost application rates.

To reduce the risks of excessive heavy metal and phosphorusaccumulations, it is not advisable to utilize compost as the solenutrient source for crop production (Manios, 2003; Shah and An-war, 2003). Therefore, the development of a well-balanced andintegrated nutrient management plan that utilizes MSWC in con-junction with mineral fertilizers is needed to improve and sustainsoil fertility (Mohammad, 1999; Manna et al., 2007; Singh et al.,2007) while minimizing detrimental environmental impacts.

To this end, we conducted 3-year field trials with six differenttreatments comprising three management strategies with twonutrient doses. The primary objective of the trials was to evaluateeffects of MSWC applied in conjunction with mineral fertilizers on:(1) physical soil properties and organic matter content; (2) soil Pstatus and wheat, cotton and rice yields and (3) heavy metal con-tents in the surface soil (0–15 cm). The study is complemented by asimple economic analysis.

Clay content (%) 19.2 14.4Bulk density (g cm�3) 1.58 1.60Porosity (cm3 cm�3) 0.43 0.40Penetration resistance (kPa) 965 1220

Chemical analysisEC (dS m�1)a 1.3 0.9pHa 7.9 8.0SOM (g kg�1) 8.2 5.0Plant available soil phosphorus (mg kg�1) 8.7 1.7

Soil plant available metals (DTPA extractable)Chromium (mg kg�1) <0.06 <0.06Cobalt (mg kg�1) 0.017 0.017Nickel (mg kg�1) 0.137 0.185Cadmium (mg kg�1) 0.021 0.045Lead (mg kg�1) 3.23 1.56Zinc (mg kg�1) 1.69 1.69

a Determined in saturated paste extract.

2. Materials and methods

2.1. Site characteristics

Three-year field trials were established in fall of 2002 to evalu-ate environmental and economical impacts of MSWC applicationsto rice–wheat and cotton–wheat cropping systems. The cotton–wheat trial was setup at the Cotton Research Raiwind substationof the Agriculture Department of Punjab (31� 23886N and 74�21686E) with a long history of desi/asiatic cotton (Gossypium arbo-retum L.) – wheat (Triticum aestivum L.) crop rotation. Annual rain-fall during the field trial ranged from 495 to 627 mm. The dailyaverage minimum air temperature during cotton season (May–October) was 25.8 �C and maximum temperature was 37.1 �C.

During wheat season (November–April), the average dailyminimum air temperature was 13.8 �C and maximum was24.9 �C. The soil of the research plots was classified as sandy loam(Typic Camborthide). Physical and chemical soil propertiesdetermined prior to the trial are listed in Table 1. The rice–wheattrial was established at the Adaptive Research Farm of the PunjabDepartment of Agriculture in Gujranwala, Pakistan (32� 21726 Nand 74� 23071 E) with an annual precipitation during the trial from626 to 761 mm. About 70% of the total precipitation occurredduring rice season in summer (July–October) and 30%during wheat season in winter. The daily average minimum airtemperature during rice growth was 22.1 �C and maximum tem-perature was 32.7 �C. During wheat season (November–April) theaverage daily minimum air temperature was 10.6 �C and maxi-mum was 20.1 �C. The soil of the research plots was classified asloam (Udic Haplustalf) with physical and chemical propertieslisted in Table 1.

2.2. Plot layouts and management

The trials were conducted in triplicate on 65-m long and 60-mwide fields that were divided into 39 plots (5-m wide and 20-mlong). In each trial 18 experimental plots (6 treatments � 3 repli-cates) were arranged based on a randomized complete block de-sign and interspaced by untreated plots of equal size to avoidadverse effects of drifting pesticides and herbicides. To allow pond-ing for rice growth, and flood irrigation of the wheat and cottoncrops, each plot was thoroughly leveled and surrounded with smallsoil ridges. The experimental plots for the wheat–rice trial wereplanted with wheat (INQLAB-91) each year in November, and inJuly of the following year rice (B-SUPER) was transplanted. A 3 to5 cm water level was continuously maintained during rice season.The plots for the wheat–cotton trial were planted with the samewheat variety in November and with desi/asiatic cotton (RAVI) inApril of the following year. Desi cotton has lower yield potentialbut very fine fiber quality and is a popular variety in the Punjab re-gion. Agronomic practices, seedbed preparation, insect/pest con-trol and irrigation were performed according to standardrecommendations of the Agriculture Department of Punjab, Paki-stan. Above ground crop residues were completely removed afterharvest. Ground water as well as surface water was used to

Table 2Evaluated treatments.

Treatment Description

T1 Mineral fertilizer (S1) – standard dose (D1)T2 Mineral fertilizer (S1) – site-specific dose (D2)T3 4:1 Mineral fertilizer/MSWC and pesticides (S2) – standard dose (D1)T4 4:1 Mineral fertilizer/MSWC and pesticides (S2) – site-specific dose

(D2)T5 4:1 Mineral fertilizer/MSWC w/o pesticides (S3) – standard dose (D1)T6 4:1 Mineral fertilizer/MSWC w/o pesticides (S3) – site-specific dose

(D2)

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flood-irrigate the fields for both wheat and cotton crops, which is acommon practice for farming communities in this area.

In both trials six treatments (T1 to T6) comprising three manage-ment strategies (S1 to S3) with two nutrient doses (D1 and D2) wereevaluated (Table 2). A 4:1 mineral fertilizer – MSWC ratio wasemployed to supply organic matter at economically feasible andbeneficial levels while keeping cumulative heavy metal levels forlong-term applications well below US EPA (1995) cumulative pol-lutant loading rate limits. Management strategies included: (1)application of mineral fertilizer as the sole nutrient supplement(S1); (2) application of mineral fertilizer in combination withMSWC at a ratio of 4:1 with pesticide and herbicide treatments(S2) and (3) combined mineral and MSWC application at a ratioof 4:1 without pesticides and herbicides (S3). Within each manage-ment strategy nutrients were applied in two different doses. Doseone (D1) was based on standard N, P and K recommendations bythe Agriculture Department of the Punjab without site-specificanalysis of soil nutrient levels. The second dose (D2) was calculatedbased on measured site-specific plant available soil phosphoruslevels and optimum PAP target values of 16 mg kg�1 for wheat–cotton and 21 mg kg�1 for wheat–rice (Akram et al., 1994). Appliedmineral fertilizer rates are listed in Table 3. Phosphorus was ap-plied as diammonium phosphate (DAP), nitrogen was applied asurea, and potassium as KCl. All P, K and half of the N fertilizer wereapplied uniformly at sowing. In the wheat–rice trial the remaininghalf of N fertilizer was applied with the first irrigation 20 days aftergermination of wheat and 35 days after transplanting rice. Fivekilogram Zn ha�1 was also applied to the rice crop one week aftertransplanting. Applied herbicides were Arelon 75 SP and Isoproturonfor wheat and Machete 60 EC for rice crops. The used pesticideswere Padan and Cartep for rice and wheat crops, respectively. Inthe wheat–cotton trial the remaining half of N fertilizer was ap-plied after the first irrigation for wheat and 40–45 days after sow-

Table 3Applied mineral fertilizer rates.

Season and crop Mineral fertilizer doses (kg ha�1)

Conventional (D1) Site-specific (D2)

N P2O5 K2O N P2O5 K2O

Wheat–rice system2002–03 Wheat 135 100 40 135 80 402003 Rice 115 100 40 115 30 402003–04 Wheat 135 100 40 135 73 402004 Rice 115 100 40 115 37 402004–05 Wheat 135 100 40 135 49 402005 Rice 115 100 40 115 72 40

Wheat–cotton system2002–03 Wheat 135 100 40 135 196 402003 Cotton 115 85 35 115 91 352003–04 Wheat 135 100 40 135 91 402004 Cotton 115 85 35 115 82 352004–05 Wheat 135 100 40 135 59 402005 Cotton 115 85 35 115 19 35

ing cotton. Applied herbicides were Arelon 75 SP and Isoproturon forwheat and Nurrelle for cotton crops. The used pesticides were Del-taphos and Imidacloprid.

The applied MSWC was provided by Waste Busters, a privateenterprise that launched a community waste management projectin Lahore, Pakistan in 1996. The MSWC originated from recycledmixed municipal solid waste and is marketed as ‘‘Green Force”compost. Waste Busters collects raw solid waste from urban cen-ters and manually separates organic material and other recyclablecontents. Windrow composting is applied to generate the com-post that is sold as soil amendment to local farming communities.The measured total heavy metal concentrations in the ‘‘GreenForce” compost were below ceiling concentrations (CC = maxi-mum concentration permitted for land application) and pollutantconcentration (PC = maximum concentration for biosolids whosetrace element pollutant additions do not require tracking) stan-dards for sewage sludge and domestic septage established bythe US Environmental Protection Agency (EPA) in 1995 (Table4); nonetheless, Cd levels were close to the CC standard. The or-ganic matter (OM) content and available N, P and K levels of the‘‘Green Force” compost were determined to be: 400 g kg�1 OM,5 g kg�1 N, 5 g kg�1 P2O5 and 10 g kg�1 K2O on dry-weight basis.The electrical conductivity (EC) and pH were measured as60 dS m�1 and 7.5, respectively. The amounts of fertilizer andMSWC required for reaching recommended PAP target values of16 and 21 mg kg�1 (adapted from McLean et al., 1982) are listedin Table 5.

The MSWC was homogenously spread over the soil surface 20–30 days before sowing and incorporated through plowing to adepth of 15-cm. Grain and paddy yields for each treatment wereobtained from manually harvested plants from three randomly dis-tributed 9-m2 subplots. Grain yield was adjusted to 140 and 120-ggrain moisture per kg for rice and wheat, respectively. Seed cottonwas hand-picked from the entire treatment plots. All abovegroundbiomass was removed after harvest.

2.3. Soil sampling and analysis

Four soil samples for chemical analyses were randomly col-lected with a 5-cm auger from the top 15-cm soil layer from eachtreatment plot immediately before the trial and after each cropharvest. The samples were thoroughly mixed, air dried, passedthrough a 2-mm sieve, and stored in sealed plastic jars. The OMcontent was determined using the chromic acid hot oxidationmethod (Walkley and Black, 1934). Soil PAP was determined usinga sodium bicarbonate extraction (Olsen and Sommers, 1982) andcolorimetry. Soil Plant available metal concentrations were mea-sured using soil–DTPA extracts (Lindsay and Norvell, 1978) andatomic absorption spectroscopy using a Spectra AA-50 unit (Var-ian, Palo Alto, CA). EC and pH were measured in saturated paste ex-tract. Three undisturbed core samples collected to a depth of 15-cm from each treatment plot before the trial and after each wheat,rice, and cotton harvest were used to determine bulk density qb

Table 4Total metal concentrations of the applied municipal solid waste compost (MSWC). USEPA (1995) established pollutant concentration (PC) standards, ceiling concentrations(CC), and cumulative pollutant loading rate limits (CPLR).

Pollutant MSWC (mg kg�1)a PC (mg kg�1)a CC (mg kg�1)a CPLR (kg ha�1)a

Cadmium 34 39 85 39Chromium 40 1200 3000 3000Copper 480 1500 4300 1500Lead 73 300 840 300Nickel 49 420 420 420Zinc 1622 2800 7500 2800

a Calculated based on the dry mass.

Table 5Municipal solid waste compost (MSWC) application rates.

Season and Crop Treatment Wheat–rice MSWC(kg ha�1)

Wheat–cotton MSWC(kg ha�1)

2002–03 Wheat T1 and T2 – –T3 and T5 4000 4000T4 and T6 3200 7800

2003 Rice/Cotton T1 and T2 – –T3 and T5 4000 3400T4 and T6 1200 3600

2003–04 Wheat T1 and T2 – –T3 and T5 4000 4000T4 and T6 2800 3600

2004 Rice/cotton T1 and T2 – –T3 and T5 4000 3400T4 and T6 1600 3400

2004–05 Wheat T1 and T2 – –T3 and T5 4000 4000T4 and T6 2000 2400

2005 Rice/cotton T1 and T2 – –T3 and T5 4000 3400T4 and T6 2800 800

Cumulative T3 and T5 24,000 22,200T4 and T6 13,600 21,600

2440 M.A. Qazi et al. / Waste Management 29 (2009) 2437–2445

(Blake and Hartge, 1986). Soil surface penetration resistance wasdetermined with a proctor penetrometer (Bradford, 1986) with across-sectional tip area of 3.23 cm2 (0.5 in2) at the time of everycrop harvest (five readings were randomly taken within each treat-ment plot).

2.4. Data analysis

Analysis of variance (ANOVA) and mean separations were per-formed using the general linear model (GLM) procedure of SASInstitute Inc. (2004). The least significant difference (LSD) proce-dure at a probability level of 0.05 was used to determine statisti-cally significant differences among treatment means. A simpleeconomic analysis was performed to evaluate net profits and va-lue-to-cost-ratios for management strategies and fertilizer doses.

3. Results and discussion

3.1. Soil physical properties

As shown in Table 6, in both trials the application of MSWC (T3

to T6) reduced bulk density and penetration resistance relative tosole mineral fertilizer treatments (T1 and T2), thereby creating amore favorable physical environment for plant growth with in-creased porosity and water holding capacity in the top soil. Thepresence (T3 and T4) or absence (T5 and T6) of herbicides and pes-

Table 6Treatment effects on soil physical properties.

Treatment Wheat–rice system Wheat–cotton system

Bulk density(g cm�3)

Penetrationresistance (kPa)

Bulk density(g cm�3)

Penetrationresistance (kPa)

T1 1.539 aA 901 b 1.598 aA 1241 a,bT2 1.526 a 1025 a 1.599 a 1264 aT3 1.453 c 621 d 1.546 b 1181 b,cT4 1.473 b 745 c 1.545 b 1158 cT5 1.448 c 593 d 1.543 b 1158 cT6 1.457 c 749 c 1.543 b 1167 c

Values at the beginning of trial1.580 965 1.598 1220

A Means within a column followed by the same letter are not significantly dif-ferent at the 5% probability level.

ticides in the MSWC treatments did not seem to have much effecton bulk density. Similar improvements of soil physical propertiesfor organic fertilizer applications were reported by Carter andSteward (1996), Haynes and Naidu (1998), Zebarth et al. (1999),Aggelides and Londra (2000), Franzluebbers (2002), Arriaga andLowery (2003) and Celik et al. (2004). A season by season compar-ison for the wheat–rice trial depicted in Fig. 1 reveals an increasingtrend in bulk density for treatments T1 and T2 where mineral fertil-izer was used as the sole nutrient supplement. All treatments uti-lizing MSWC (T3 to T6) as nutrient and organic carbon source showa decreasing trend over the 3-year trial period, which points to im-proved physical conditions for plant growth. It is interesting tonote that the different MSWC application rates (Table 5) did notlead to significant differences in bulk densities. The same seasonby season trend was observed in the wheat–cotton trial.

Season by season comparison of penetration resistance for bothtrials showed a slightly different picture. The penetration resis-tance of mineral fertilizer plots (T1 and T2) was well above theMSCW plots (T3 to T6) throughout the trial period. Treatments withsite-specific MSWC application rate (T4 and T6) in turn showedhigher penetration resistance than treatments with the conven-tional MSWC rate (T3 and T5). Again, the presence (T3 and T4) or ab-sence (T5 and T6) of herbicides and pesticides in the MSWCtreatments do not seem to have much effect penetrationresistance.

3.2. Soil organic matter

SOM contents after 3-years of field trials are listed in Table 7.Though in both trials increases in SOM relative to pretrial statuswere observed, there were no statistically significant differencesamong treatments. This is somewhat surprising given the fact thatno MSWC or other organic amendments where applied in treat-ments T1 and T2. Cadisch and Giller (1997) stated that the amountof organic matter accumulation in soils relative to the organic fer-tilizer application rate can vary significantly depending on the cli-matic and biophysical boundary conditions for decomposition andmineralization. While many studies have shown that a consider-able increase in SOM can be achieved through addition of organicwaste (e.g., Aoyama et al., 1999; Montemurro et al., 2006) our datashow no significant differences in SOM between investigated treat-ments. For the semi-arid climatic conditions of the Punjab region,the soil properties of the trial plots and prevailing managementpractices for the cotton–wheat and rice–wheat cropping systems,the addition of new organic matter (i.e., MSWC application) anddecomposition and mineralization processes seem to be in balanceafter the 3-year trial period. This is also evident from the season byseason comparison of SOM contents depicted in Fig. 2 for the rice–

Fig. 1. Soil bulk densities observed for the wheat–rice cropping system over the 3-year trial period (error bars indicate the standard error of means).

Table 7Organic matter and soil phosphorus status at the end of the 3-year trials.

Treatment Wheat–rice system Wheat–cotton system

Organic Carbon(g kg�1)

Phosphorus(mg kg�1)

Organic Carbon(g kg�1)

Phosphorus(mg kg�1)

T1 8.4 aA 17.0 a 6.8 aA 12.3 aT2 9.0 a 20.6 a 7.5 a,b 12.2 aT3 8.8 a 17.0 a 7.1 a 11.9 aT4 8.6 a 18.4 a 7.1 a 10.7 aT5 8.5 a 20.9 a 7.9 a,b 12.9 aT6 9.0 a 22.0 a 8.9 b 12.3 a

Values at the beginning of trial8.2 8.7 5.0 1.7

A Means within a column followed by the same letter are not significantly dif-ferent at the 5% probability level.

Fig. 2. Soil organic carbon contents observed for the wheat–rice cropping systemover the 3-year trial period (error bars indicate the standard error of means).

M.A. Qazi et al. / Waste Management 29 (2009) 2437–2445 2441

wheat cropping system. After initial fluctuations of SOM contentsduring cropping seasons one to four, SOM values seem to approacha steady level of about 9.0 g kg�1 in seasons five and six.

The slight increase of SOM relative to the pretrial levels that weobserved for the mineral fertilizer treatments (T1 and T2) is inagreement with findings reported by Zhang et al. (2006) and canbe attributed to an increase in belowground biomass (in the yearsprior to the trial only small amounts of urea were sporadically ap-plied to the plots).

3.3. Soil plant available phosphorus

In course of the 3-year field trials significant increases of plantavailable phosphorus levels relative to the initial status for allmanagement strategies and fertilizer doses were observed (Table7). Though there were some seasonal variations observed in thewheat–cotton trial, the overall phosphorus level in the uppermost15-cm almost sextupled after 3 years and was close to the targetsufficiency level of 16 mg kg�1 (please note that no phosphorusfertilizer was applied in the years prior to the field trials). For thewheat–rice trial the phosphorus levels more than doubled for alltreatments after three years and were close to the target suffi-ciency level of 21 mg kg�1. Based on the obtained data we can statethat after 3 years we did not measure excessive plant availablephosphorus accumulations in the surface soil for all investigatedtreatments. However, there were no statistically significant differ-ences among any type of applications (T1 to T6). This may be due tothe fact that over the trial period similar P2O5 rates were appliedwith mineral fertilizer and MSWC for the conventional and thesite-specific doses, respectively (Table 3).

3.4. Heavy metals accumulation

To evaluate potential detrimental accumulation of compost-borne heavy metals in the surface soil, we specifically tested forplant available (DTPA extractable) cadmium (Cd), chromium (Cr),nickel (Ni), lead (Pb) and zinc (Zn). The chemical analysis of ‘‘GreenForce” compost used in this study yielded total heavy metal con-centrations below US EPA (1995) established pollutant concentra-tion (PC) standards for sewage sludge and domestic septage (Table4). Based on soil analysis prior to the trial, see Table 1, the loam andsandy loam soils of the field plots can be classified as soils withnatural concentrations of Cd, Cr, Ni, Pb and Zn (Kabata-Pendiaset al., 1993).

For the wheat–rice trial, 3 years of MSWC applications in-creased the levels of Cd and Zn in the 0–15 cm depth by up to0.4 and 18 mg/kg, respectively. This may explain why plant avail-able (DTPA extractable) soil cadmium levels (0.15 cm) showedlarge increases relative to the pretrial levels, see Fig. 3. In particu-lar, soil plant available Cd levels nearly doubled for all manage-ment strategies and fertilizer doses. However, there were nostatistically significant differences among the mineral fertilizertreatments (T1 and T2) and the MSWC treatments (T3 to T6). Thissuggests that cadmium may have also originated from mineral fer-tilizer sources. A study by Merry and Tiller (1991) established cor-relation between soil Cd levels and extractable P in pasture soils ofSouth Australia, indicating that P fertilizer applications were a sig-nificant source for cadmium. All pre- and post-trial DTPA extract-able chromium (Cr) levels were below the 0.06 mg kg�1 AASdetection limit and are therefore not shown in Fig. 3. The mean val-ues of soil DTPA extractable nickel (Ni) did not show significant dif-ferences among all evaluated management strategies and fertilizerdoses (Fig. 3), and the levels did not significantly increase relativeto the pretrial levels. Lead (Pb) and zinc (Zn) DTPA extractable lev-els, were not significantly different among treatments, but theyshowed small increases relative to the pretrial levels (Fig. 3). Insummary, large increases in DTPA extractable Cd, and Zn in thesurface soil layer were observed for all treatments. Whereas, in-creases in soil Ni and Pb appeared to be minimal during the trialperiod. Presented data for the wheat–cotton trial (Fig. 3) indicatethat the application of MSWC did not significantly increase theconcentration of any of the observed DTPA-extractable metals overthe 3-year trial period relative to pretrial levels; they remained al-most unchanged. The levels of Zn, Cd, Cr, Pb and Ni were statisti-cally non-significant different between all six treatments. Thesefindings are in good agreement with data reported by Montemurroet al. (2005a,b) and Cala et al. (2005), who did not observe elevatedheavy metal concentrations in surface soils due to biosolid applica-tions. The observed Zn, and in particular Cd enrichment in loamsoil for the rice–wheat cropping system were probably due tothe much lower initial soil Zn and Cd levels. On the other handthe much higher natural Cd of sandy loam soil used for the cot-ton–wheat trial may have helped mask the three years of MSWCadditions.

3.5. Crop yields

The 3-year cumulative grain and straw yields for the wheat–ricesystem listed in Table 8 show that wheat grain yield was not sta-tistically significant different between treatments over the threeyear period. However, rice grain yields were significantly differentamong management strategies, but not between fertilizer doses.The data indicate that treatments T3 and T4 (MSWC applied in con-junction with mineral fertilizer and pesticides and herbicides treat-ments) had the highest (statistically significant) yields followed bytreatments T1 and T2 where mineral fertilizer was the sole nutrientsupplement. Season by season comparisons of yields show steady

Fig. 3. Heavy metal levels (DTPA extractable) at the end of the 3-year trials relative to pretrial levels (error bars indicate the standard error of means; means with the sameletter on top of the error bar are not significantly different at the 5% probability level).

Table 8Effects of management strategies and fertilizer doses on wheat, rice, and cotton yields.

Treatment Cumulative grain yield (kg ha�1) Cumulative straw yield (kg ha�1)

Wheat Rice Wheat Rice

Wheat–rice systemT1 8713 aA 11107 b,c 12531 b,c 39744 a,bT2 8104 a 11693 b 11607 b,c 40719 aT3 8894 a 12641 a 13298 a,b,c 37589 bT4 8090 a 13118 a 10676 c 39256 a,bT5 8541 a 10389 c 13893 a,b 37085 bT6 9000 a 10304 c 15885 a 39760 a,b

Wheat–cotton systemWheat Cotton Wheat Cotton

T1 9661 aA 2496 a 16720 a 12020 aT2 11305 b,c 2660 b 18265 a,b 12233 aT3 11280 b,c 2361 c 18554 a,b 12167 aT4 11367 c 3037 d 20076 b 14033 bT5 10406 a,b 2961 e 18167 a,b 14020 bT6 10555 a,b,c 2962 e 18658 a,b 13000 c

A Means within a column followed by the same letter are not significantly different at the 5% probability level.

2442 M.A. Qazi et al. / Waste Management 29 (2009) 2437–2445

increases in wheat and rice grain yields over the 3-year trial period,indicating a general increase in soil fertility in all treatments. Sig-nificantly higher wheat straw yields were observed in treatmentsT5 and T6 (MSWC/mineral fertilizer without pesticides) over the3-year trial period (Table 8). This can be linked to improved phys-ical growth conditions (reduced bulk density and penetrationresistance). In contrast, significantly higher rice straw yields wereobserved for treatments T2, T4 and T6 (site-specific fertilizer appli-cation rates) when compared to the treatments with standardapplication rates. No significant differences in wheat straw yieldswere observed among management strategies. Season by seasoncomparison showed that grain and straw yields increased steadilyfor all treatments and fertilizer application rates over the 3-yeartrial period. In summary, repeated applications of MSWC to loam

soil under rice–wheat cropping systems and proper insect pestmanagement improved rice yields significantly. Singh et al.(2001) noted an increase in paddy yield with the use of farmyardand green manure in combination with mineral fertilizer. Zakaet al. (2003) observed significant increase in rice and wheat yieldswith the use of farmyard manure (FYM), rice straw, and Sesbania.Similarly, numerous other studies (Selvakumari et al., 2000; Mish-ra and Sharma, 1997; Ahmad et al., 2002; Parmer and Sharma,2002) show increased rice and wheat yields when organic fertilizerwas applied as sole nutrient source or in combination with mineralfertilizers.

For the wheat–cotton system cumulative wheat yields were notsignificantly different among most treatments (Table 8). Only T1,where mineral fertilizer was applied at the standard recommended

M.A. Qazi et al. / Waste Management 29 (2009) 2437–2445 2443

rate, showed statistically significant lower yield than treatments T2

to T4. Overall, there is no clear indication that MSWC application atsite-specific or standard rates lead to significant increase or de-crease of wheat grain yield. Singer et al. (2004) reported similarfindings indicating that the effect of compost application on wheatgrain yield is statistically not significant different from mineral fer-tilizer applications. Similar results were also obtained for sun-flower (Montemurro et al., 2005b). However, the statistical trendsuggests that site-specific fertilizer rate yields (T2, T4 and T6) wereslightly elevated relative to the treatments with standard fertilizerapplication rates. For cotton, statistically significant differences be-tween different nutrient doses and management strategies wereobserved. Repeated MSWC applications in combination with min-eral fertilizer at site-specific doses (T2 and T4) showed highest cot-ton yields (Table 8). The highest yield was obtained with treatmentT4. It is interesting to note that higher yields were obtained withfertilizer applications adjusted to site-specific soil P levels (T2, T4

and T6) despite the fact that the cumulative P2O5 application rateof 538 kg P2O5 ha�1 was slightly below the treatments where fertil-izer was applied based on standard recommended rates with555 kg P2O5 ha�1 (T1, T3 and T5). This is a promising result fromenvironmental and economical point of view that shows the poten-tial positive impact of adjusting mineral fertilizer and MSWC appli-cation rates to soil test P levels.

This positive impact was not visible for cumulative wheat strawor cotton biomass production. However, a season to season com-parison of wheat straw yields showed an increase in growing sea-sons three and five. Cotton straw yield remained fairly constantduring the trial period. The same seasonal trends were observedfor grain yields.

3.6. Economical considerations

New management plans for rice–wheat and cotton–wheat crop-ping systems within the Punjab region of Pakistan cannot beadopted unless tangible economical benefits to the local farmingcommunities can be demonstrated. To this end, a simple economicanalysis was performed to calculate the cumulative net profit andvalue-to-cost-ratio for each trial and treatment (Table 9). This wasdone using commodity sales prices including gross returns (GR)from selling cotton seeds, wheat and rice grains, and straw at localmarkets, and the total costs of production (TCP), including labor,MSWC, mineral fertilizer, herbicides, pesticides, wheat and cottonseeds, rice transplants and irrigation. The net profit (NP) was calcu-lated by subtracting TCP from GR, and the value to cost ratio (VCR)was determined as the ratio of GR and TCP. However, difficult toquantify benefits to the Pakistani national economy (such as thereduction of municipal solid waste that would otherwise be depos-ited in unlined open landfills and associated benefits for publichealth), were not included in this economic study.

For the wheat–rice trial the cumulative net profit was highestfor treatments T1, T2 (mineral fertilizer standard dose and site-spe-cific application rates), treatment T4 (MSWC/mineral fertilizer with

Table 9Effects of management strategies and fertilizer doses cumulative net profits and value–co

Treatment Wheat–rice system

Cumulative net profit USD ha�1 Value–cost ra

T1 4551 aA 5.04 bT2 4695 a 5.76 aT3 4326 a,b 3.51 dT4 4603 a 4.49 cT5 3960 b 3.59 dT6 4587 a 5.07 b

A Means within a column followed by the same letter are not significantly different a

pesticides) and treatment T6 (MSWC/mineral fertilizer w/o pesti-cides) (Table 9). A comparison of value-to-cost-ratios (VCR) showsslightly different results. The VCR was highest for treatment T2 fol-lowed by treatment T6, treatment T1, and treatment T4. Again, site-specific fertilizer application rates yield economically betterresults.

Cumulative NPs and VCRs for the cotton–wheat cropping sys-tem over the 3-year trial period (Table 9) confirm results obtainedfor the rice–wheat system. All treatments with fertilizer applica-tion rates adjusted to soil test P levels (T2, T4 and T6) yield higherNPs and VCRs than treatments with standard recommended fertil-izer rates (T1, T3 and T5). The highest cumulative NP was obtainedfor treatment T2, where only mineral fertilizer was applied basedon site-specific soil test P. However, there is no statistically signif-icant difference to treatment T4 with combined site-specific MSWC– mineral fertilizer application and pest management.

Results clearly indicate that site-specific fertilizer applicationrates determined based on the soil plant available phosphorus lev-els are more likely to yield higher economical returns than usingcommonly applied standard fertilizer rates recommended by theAgriculture Department of Punjab. This finding is important assite-specific rates also reduce detrimental environmental impactsof field-applied agrochemicals. It is also important to point out thatthe cumulative net profits of treatments with site-specific MSWC/mineral fertilizer applications (T4 and T6) were not much differentfrom treatment T2 where mineral fertilizer was applied at site-spe-cific rate. The slightly higher returns for treatment T2 are due to therelatively high costs for MSWC (about 3.3 cents kg�1). Not account-ing for the benefits for the national Pakistani economy (i.e. reduc-tion in municipal solid waste), potentially long-term beneficialeffects of MSWC amendments for soil fertility and physical proper-ties, and lower environmental impacts, the application of mineralfertilizer based on site-specific nutrient levels seems to be the mosteconomically beneficial strategy for local farming communities.However, if MSWC prices would be subsidized by the governmentas is the case for mineral fertilizers, treatments with MSWC/min-eral fertilizer at a ratio of 1:4 applied based on soil test P wouldbe a viable alternative. This use of MSWC and fertilizer could yieldbetter economic return than sole mineral fertilizer application.

4. Summary and conclusions

To evaluate environmental and economic impacts of MSWCapplications to rice–wheat and cotton–wheat cropping systemsin Punjab, Pakistan, 3-year field trials were conducted with six dif-ferent treatments comprising three management strategies withtwo nutrient doses. After three years significant improvements insoil physical properties for all treatments with MSWC were ob-served. Although quantitatively small, statistically significantreductions in bulk density and penetration resistance were mea-sured in plots with MSWC relative to those where only mineral fer-tilizer was applied. Plant available phosphorus levels increased

st ratios.

Wheat–cotton system

tio Cumulative net profit USD ha�1 Value–cost ratio

2847 a,cA 3.51 a3293 b 3.88 b2615 c 2.56 c3080 a,b 2.84 d2858 a,c 2.79 d2900 a 2.83 d

t the 5% probability level.

2444 M.A. Qazi et al. / Waste Management 29 (2009) 2437–2445

considerably relative to the initial status in all management strat-egies and fertilizer doses. While seasonal variations in plant avail-able P were observed in rice, cotton, and wheat crops, phosphoruslevels in the uppermost 15-cm of soil significantly increased andremained close to the recommended target sufficiency levels of16 and 21 mg kg�1 for the cotton–wheat and rice–wheat systems,respectively. No statistically significant differences between solemineral fertilizer application practice and the MSWC treatmentswere observed. Soil organic matter did not show any statisticallysignificant increase for any trials and treatments during the 3-yearperiod. Three years are probably not sufficient to evaluatelong-term impacts of continued MSWC applications on soil organicmatter accumulation. The levels of DTPA extractable heavy metalsincreased in the top layer following 3 years of MSWC and fertilizerapplications but were not found to be of concern, pending futureresearch on crop metal uptake and leaching.

A simple economic analysis revealed higher net profits for treat-ments with site-specific fertilizer application rates, though there isno statistically significant difference among management strate-gies. The VCRs for sole mineral fertilizer applications at site-spe-cific rates were higher than for treatments containing MSWC.The major reason for this difference is the high price local farmingcommunities pay for municipal solid waste compost, while min-eral fertilizer is relatively cheap and subsidized by the government.Considering benefits to the Pakistani national economy (i.e.,reduction of municipal solid waste for open landfill disposal), thecombined application of MSWC and mineral fertilizer in environ-mentally safe quantities is a viable option for sustaining andimproving soil fertility in rice–wheat and cotton–wheat systems.However, without governmental subsidies for deferring the cur-rently relatively high costs for MSWC it will be challenging to con-vince local farmers to use MSWC as a supplement to mineralfertilizer.

Acknowledgements

The authors express their gratitude to the Higher EducationCommission of Pakistan for sponsoring Mr. Akram Qazi’s visit atthe University of Arizona. Special thanks go to Jeffrey Silvertooth(UA) and Phyllis Berger (UA) for their insightful comments on anearlier version of the manuscript.

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