NITROGEN MINERALIZATION OF MUNICIPAL SOLID WASTES IN SOILS DURING LABORATORY INCUBATIONS

Transcription

1 Sarhad J. Agric. Vol., No., 7 NITROGEN MINERALIZATION OF MUNICIPAL SOLID WASTES IN SOILS DURING LABORATORY INCUBATIONS Zahir Shah, Shabana Roshan, Zahid Shah and M. Tariq ABSTRACT Sustainable land application of organic wastes need sound knowledge of the chemical composition and N mineralization rates. This study was conducted to investigate the N mineralization of municipal solid wastes (MSW) in two different soils using a lab incubation experiment at NWFP Agricultural University, Peshawar during -. MSW in Peshawar were collected from four locations viz. vegetable market, Town-, Town and University. Field moist soil collected from two soil series (Pirsabak and Katti Khel) at cm were amended with dried ground (< mm) MSW at three rates equivalent to, or kg N ha - and then incubated in ventilated plastic containers at o C. Sub-soil samples were taken out at, 8,,, 6, 78 and 9 days and analyzed for mineral N. The results revealed that application of MSW significantly (P<.) increased total mineral N by fold compared to the control. Mineral N productions and N mineralization rates exhibited temporal variations and varied significantly with waste locations and their application rates and soil types. During the first days of incubation, net N mineralization rates were either negative (immobilization) or very low as evident from their low mineral N production. Immobilization could be attributed to the lack of readily mineralizable organic substrates in MSW at the time of their application or due to the fact that added MSW was fresh and was not stabilized. After days incubation period, soils amended with MSW exhibited a clear phase of net N mineralization. At day 78 and 9, net N mineralization rates in MSW treated soils were significantly higher than those of the control. Net N mineralization rates increased from.6 mg N kg - soil day - in control to mg N kg - soil day - in MSW treated soils representing 9 times increase over control. Over all MSW at kg N ha - rates produced more mineral N than that at kg. The N mineralization rate was relatively high in Katekhel than in Pirsabak soil series indicating that the presence of salts in Katekhel series had no adverse effect on the N mineralization process. These results suggested that dried and ground MSW can be used on agricultural lands as a source of N but need to be applied at least days before sowing of a crop. INTRODUCTION The municipal solid wastes (MSW) of the provincial capital Peshawar city are dumped on open ground at three locations close to the residential areas. The open dumps not only cause unpleasant odor and nuisance but also pose a potential risk of spreading infectious diseases in the nearby areas. There is also a great risk of site contamination with heavy metals such as Zn, Cu, Fe, Mn, Cr, Pb, Cd and Ni and leaching of toxic materials to surface and ground waters. The discharge of municipal wastes into water bodies reduces its quality by causing eutrophication due to its high N, P and C contents, increases biochemical oxygen demand (BOD) in water, and causes microbiological contamination by various bacteria (i.e. Faecal Coliforms and E. Coli). Similarly heavy metals from MSW may enter into food chain through fish and pose a significant health risk to human. According to one report, about tons of municipal solid wastes are produced per day in Peshawar of which only tons are picked up (Director General, City, Municipal and Dev. Depit.,, Personal Communic.). It has been found that MSW of Peshawar city contain considerable amounts of N and K, and small amount of P (Shah and Anwar, ; Shah et al. ). The same paper mentioned that the MSW of Peshawar city contained small amounts of heavy metals and were therefore recommended for use on agricultural lands as organic fertilizer/conditioner after necessary processing. Land application of MSW may be the best option as most organic wastes are valuable resource of plant nutrients especially N, P, K, S, Ca, Mg and organic C and may therefore improve physical, chemical and biological properties of a soil (Cameron et al. 997; Zaman et al. 998; Zaman et al. a; Shah and Anwar, ). Both under laboratory and field conditions, N mineralization rates and microbial biomass have been shown to increase after a single application of organic wastes (Paul and Beauchamp, 996; Zaman et al. 999a and b, Zaman et al. b). Even today in agriculturally advanced regions of China, Japan, India, France, Australia and New Zealand, the total quantity of nutrients recycled back to agricultural land in organic wastes is still greater than that applied in chemical fertilizers. After World War, the introduction of chemical fertilizers as readily available source of plant nutrients resulted in the production and accumulation of large amounts of organic wastes worldwide. In many countries, large amounts of organic wastes are disposed through burning in the incinerators, dumping in the landfills and flushing into rivers and oceans. Such methods of waste disposal are causing environmental problems such as contamination/pollution of surface and ground water (encouraging eutrophication and enrichment of drinking water with nitrate), air (emission of particulates, dioxin, greenhouse and ozone depleting gases to the atmosphere), and soils with heavy metals Department of Soil & Environmental Sciences, NWFP Agricultural University, Peshawar - Pakistan

2 Zahir Shah et al. Nitrogen utilization of municipal solid 68 and other organic substances. Therefore safe and efficient disposal of organic waste through useful means of recycling are critical to avoid environmental problems. However soil may not be regarded as a dumping place for organic wastes (Cameron et al. 997) and every waste has to be evaluated for its physical, chemical and biological activities before it is recommended for use on agricultural lands. It is therefore critical to enhance our understanding of the efficient recycling of the municipal solid wastes by determining their N mineralization rates. This study was undertaken to measure rates of N mineralization in soils amended with dried and ground (< mm) MSW collected from Peshawar city of North West Frontier Province, Pakistan. MATERIALS AND METHODS Characteristics of Municipal Solid Wastes Municipal solid wastes (MSW) samples were collected from four different locations viz. city vegetable market, dumping grounds of city garbage for Town-, Town, and at near Agricultural University in Peshawar during -. From each dumping ground, samples were randomly taken from different spots and then composited. MSW samples were transferred to the shed of Agricultural University Research Farm, Peshawar and spread on a plastic sheet in a shade to dry. Non-biodegradable materials such as glass, papers and plastic bags were removed and then ground (<. mm). Characteristics of the said MSW samples are described elsewhere (Shah et al. ). Description of Soil Series Two soil series viz. Pirsabak and Katti Khel located near Charsadda on Chrasadda-Nowshera road were used in this study. Pirsabak Soil Series The soil of this series was silty loam, calcareous, non-saline and non-sodic for more than ft and was classified as coarse loamy mixed hyperthermic typic ustocript. Katti Khel Soil Series The soil of this series had the same characteristics as of Pirsabak soil series except that this soil was saline and saline-sodic and was classified as course loamy mixed hyperthermic acric haplaquepts. Soil Sampling and Processing Soil samples at cm depth were collected from selected soil series (viz. Pirsabak and Katti Khel) located in District Charsadda at Nisata on Charsadda- Nowshera Road. During sampling, some characteristics of soils were tested in the field to confirm that samples were taken from the right series. For example, both soils showed effervescence with HCl and observed the presence of cankers down the soil profile indicated the calcareousness characteristics of both soils. Both soils were nonsticky upon wetting exhibiting lack of clay. After treatment with thymol blue, the colour of Pirsabak soil turned pink to red while that of Katti Khel soil turned blue indicating the presence of salts in the later than in the former. After collection, soil samples were broken down gently by hand. Stones and visible plant roots and litters were removed and sieved (< mm). Field moist soil sample were used in the incubation. Soil from Pirsabak series was silty loam, had a ph of 9., organic matter.8% and was calcareous, non-saline non-sodic in the top 9 cm soil depth. Katti Khel soil was silty loam with a ph of 9.9, organic matter.6 % and was saline and saline-sodic. Incubation Procedure A non-leaching incubation technique was used to determine N mineralization rates (Abbasi et al., ). Field moist soil samples ( g at gravimetric water content of 9 %) were amended with dried and ground (< mm) MSW at three rates equivalent to, and kg N ha -. The MSW-soil mixture was transferred to ventilated plastic container and incubated at o C for 9 days. To maintain the constant moisture content during the incubation period, the soil-waste mixture in plastic containers was weighed every days and the moisture losses were adjusted by adding distilled water. Sub-soil samples ( g oven) were taken out from each container at, 8,,, 6, 78 and 9 days and analyzed for soil mineral N (NH + -N and NO - -N). Soil Analysis Mineral N content in soil samples was determined by the steam distillation method as described by Mulvaney (996), and total N in soil or waste samples was determined by the regular Kjeldahl method as described by Bremner (996). Soil ph and EC were determined in soil:water suspension (:) using ph-meter (Model German Type B- using calomel electrode) for the former and Electrical Conductivity Meter for the later (Thomas, 996). The gravimetric water in soil was determined by drying samples in oven at o C for hrs. Net mineralization rates (mg N kg - soil day - ) in control and MSW amended soils were calculated by subtracting the pre-mineral N concentration from the

3 Sarhad J. Agric. Vol., No., 7 68 post mineral N concentration at specific incubation time divided by the number of incubation days between those sampling dates (Abbasi et al., ). Statistical Design and Analyses The two soil series (Pirsabak and Katti Khel), municipal solid wastes collected from different locations (Vegetable market, Town-, Town and University) and three rates (no N, kg N and kg N ha - ) were replicated times in a xxx factorial experiment. Statistical analyses were performed on data by using analysis of variance (ANOVA). Least significant difference values (LSD) were calculated only when the treatment or their two or three-ways interaction effects were significant. All the analyses were performed using SYSTAT (99). The graphs were made in graphic package using Sigma-Plot-version-8. RESULTS AND DISCUSSION Total Mineral N over 9 Days Incubation Period The concentrations of total mineral N (sum of N from all sampling dates) in both Pirsabak and Katti Khel soil series over 9 days incubation were significantly (P<.) affected by MSW locations and their application rates, and their two or three-ways interactions. The three-way interaction (soil x application rates x waste location) was significant at P<. and shown in Figure a-b. The application of MSW to Pirsabak soils increased total mineral N concentrations by times compared to the control (Fig. a). Total mineral N also varied significantly with the locations of MSW. The highest amount of N was released by soil amended with MSW collected from Town- followed by Town and University; while the lowest amount was released from that of vegetable market wastes. The two application rates of MSW did not exhibit consistent trend and changed with waste location. Soil treated with MSW from Town and University at kg N ha - released more mineral N than those at kg N ha - ; while opposite trend was observed in soil treated with MSW from vegetable market. In Katti Khel soils, total mineral N was also significantly higher in MSW treated soils than the control and varied with locations and application rates of MSW (Fig. b). Soil amended with MSW collected from university had higher total mineral N than those of Town-, Town and vegetable market. This order of N production was different from that of Pirsabak soils, which could be due to the difference in chemical properties of the two soils. Unlike in soil from Pirsabak series, higher application rates of MSW at kg N ha - released more mineral N than at kg N ha - in soil from Katti Khel series. The control (with no waste amendment) treatment showed that Pirsabak soil released more mineral N than Katti Khel soil, but such differences were statistically nonsignificant (P<.). Net N Mineralization Rates (mg N kg - soil day - ) During 9 Days Incubation Soil series, locations of MSW and their application rates had a significant (P<.) effect on net N mineralization rates during the incubation. In Pirsabak soil, net N mineralization rates (mg N kg - soil day - ) in MSW treated soils and in the control were either very minimal or negative indicating immobilization phase during the first days of incubation (Fig a-d). Net N mineralization, the difference between gross N mineralization and microbial immobilization, occurs only when the decomposing organic substrates with low C:N ratios (<) release more mineral N than the microbial demand. This further implies that the added MSW did not have enough readily available sources of organic N at the time of its application. Immobilization phase could also be due to the fact that the added MSW was fresh and was not biologically stabilized at the time of application. Our results are consistent with those of Zaman et a.l (a) and Iglesias () who also observed immobilization phase in soil treated with organic wastes during incubation. Our study therefore demonstrates that fresh MSW may not be applied to agricultural crops in immediate demand of N to avoid N deficiency. Other organic wastes (wheat straw, mung residues, peas residues) were also reported to have encouraged N immobilization during the first few weeks of their application to soil (Shah et al., ; Shah and Khan, ). Therefore MSW should be rather composted to stabilize its biological activity or may be applied in combination with chemical N fertilizer. At day, net N mineralization rates in all treatments increased but differences between MSW treated and the untreated control soils were not significant. At day 78 and 9, the net N mineralization rates in MSW treated soils were significantly higher than that in the control. The net N mineralization increased from.6 mg N kg - soil day - in control to mg N kg - soil day - in MSW treated soils representing 9 times increase over the control. The higher net N mineralization after 6 days indicates that the organic substrates in the added MSW became matured and stabilized. Nitrogen in organic wastes applied to soil may be separated into five pools: (i) nitrate; (ii) exchangeable ammonium ions and other nitrogenous materials which can be readily converted to

4 Zahir Shah et al. Nitrogen utilization of municipal solid 68 ammonium; (iii) organic N compounds which are potentially available and constitute the bulk of the mineralizable substrate; (iv) microbial biomass and (v) essentially unavailable N which is resistant to microbial attack and mineralization processes (Jenkinson and Ladd, 98; Juma and Paul, 98). Pool (v) would be the main source of N immobilization during the first days of incubation (Fig. ) and pools (iii) and (iv) serve as the substrate for rapid release of mineral N at day 78 and 9. It is clear from our study that the organic N in MSW would only be available to plants after it is stabilized after 6 days. These results help to explain the N mineralization phase observed in other studies in the composted city wastes (Cheneby et al., 99; Iglesias, ). The effect of the two application rates of MSW on net N mineralization was not consistent and varied with incubation time and locations of MSW. For example, at day 78 in vegetable market wastes, the two application rates exhibited similar mineralization rates (.87 mg N kg - soil day - ), but at day 9, the application rate of MSW at kg N ha - resulted in significantly higher mineralization rates ( mg N kg - soil day - ) than that (.6 mg N kg - soil day - ) at kg N ha -. Similar inconsistent net N mineralization trends were observed in MSW from other locations. Overall N mineralization rates in soil treated with MSW from different locations are ranked in the order: vegetable market > town- > town > university. In Katti Khel soil series, the net N mineralization rates in MSW treated soils were also negative during the first days of incubation and then became positive at day. After day 6, net N mineralization rates in MSW treated soils increased by 8 to folds compared to the control. Net N mineralization rates in soil amended with MSW at kg N ha - were higher than that at kg N ha -, but such differences were not statistically significant at α.. However, net N mineralization was significantly higher in the wastes amended than in the control soil. By comparing the MSW from four locations, the net N mineralization rates were in the order: University > Vegetable market > Town- > Town. CONCLUSION AND RECOMMENDATIONS The N mineralization rates in MSW treated soils exhibited temporal variations during the incubation. During the first 6 days of incubation, mineral N concentrations in treated soils were minimal due to immobilization phase and increased afterward due to faster mineralization. The N mineralization rates varied with locations and application rates of MSW. The present study has improved our understanding regarding N mineralization rates of MSW as affected by soil types, wastes location and application rates. However, the results have raised a number of important issues, which need to be addressed in future research. For example, we need to improve our understanding of the long-term effect of land application of MSW on soil quality such as accumulation of heavy metals in surface and subsurface soils, N mineralization rates, microbiological and enzyme activity. Acknowledgments This study was part of an ALP funded project on recycling of organic wastes for sustainable agriculture. The authors wish to thank PARC, Islamabad for providing funds for this study through ALP project.

5 Sarhad J. Agric. Vol., No., 7 68 Total minieral N (mg N kg - soil) over 9 days 7 No N kg N ha - kg N ha - Pirsabak soil series vegetable market Town- Town University Total minieral N (mg N kg - soil) over 9 days 7 Katti Khel soil series vegetable market Town- Town University Fig. Total mineral N production (mg N kg- soil) over 9 days incubation period. Vertical bars indicate LSD value at alpha..

6 Zahir Shah et al. Nitrogen utilization of municipal solid 686 Net N mineralization rate (mg N kg - soil day - ) - a Vegetable market waste No N N at kg N ha - N at kg N ha - day-8 day day- day-6 day-78 day-9 - b Town- waste day-8 day day- day-6 day-78 day-9 Net N mineralization rate (mg N kg - soil day - ) - c Town waste day-8 day day- day-6 day-78 day-9 - d University waste day-8 day day- day-6 day-78 day-9 Fig. Incubation time (days) Net N mineralization rates (mg N kg - soil day - ) at individual sampling dates in Pirsabak soil series amended with different rates of municipal solid wastes collected from four locations in Peshawar. Vertical bars indicate LSD at α..

7 Sarhad J. Agric. Vol., No., Net N mineralization rate (mg N kg - soil day - ) - a Vegetable market waste No N N at kg N ha - N at kg N ha - day-8 day day- day-6 day-78 day-9 - b Town- waste day-8 day day- day-6 day-78 day-9 Net N mineralization rate (mg N kg - soil day - ) - c Town waste day-8 day day- day-6 day-78 day-9 - d University waste day-8 day day- day-6 day-78 day-9 Incubation time (days) Fig. Net N mineralization rates (mg N kg - soil day - ) at individual sampling dates in Katti Khel soil series amended with different rates of municipal solid wastes collected from four locations in Peshawar. Vertical bars indicate LSD at α.. REFERENCES Abbasi, M. K., Z. Shah and W.A. Adams.. Mineralization and nitrification potential of grassland soils at shallow depth during laboratory incubation. J. Plant Nutr. Soil Sci. 6: 97-. Abbasi, M. K., Z. Shah and W.A. Adams.. Effect of the nitrification inhibitor nytrapyrin on the fate of nitrogen applied to a soil incubated under laboratory conditions. J. Plant Nutr. Soil Sci. 66: -6. Bremner, J.M Nitrogen-Total. Pages. 8-. In Sparks, D.L. (ed.). Methods of Soil Analysis: Part -Chemical methods. Soil Sci. Soc. Amer., Book Series No.. SSSA and ASA Inc. Madison. WI. USA. Cameron, K. C., H. J. Di and R. G. McLaren Is soil an appropriate dumping ground for our wastes? Aust. J. Soil Res. : 99. Cheneby, D., B. Nicolardot, B. Godden and M. Penninckx. 99. Mineralization of composted N, labelled farmyard manure during soil incubations. Biol. Agric. Hort. (): 6. Iglesias, J.E.. Nitrogen availability from a mature urban compost determined by the N isotope

8 Zahir Shah et al. Nitrogen utilization of municipal solid 688 dilution method. Soil Biol. Biochem. (): 9. Jenkinson, D.S. and J.N. Ladd. 98. Microbial biomass in soil: Measurement and turnover. Pages -7. In Paul E.A. and J.N. Ladd (ed.) Soil Biochemistry. Vol.. Marcel Dekker, New York. Juma, N. G., and E. A. Paul. 98. Mineralizable soil nitrogen: Amounts and extractability ratios. Soil Sci. Soc. Amer. J. 8: Mulvaney, R.L Nitrogen-Inorganic Forms. Pages. -8. In Sparks, D.L. (ed.). Methods of Soil Analysis: Part -Chemical methods. Soil Sci. Soc. Amer., Book Series No.. SSSA and ASA Inc. Madison. WI. USA. Paul, J. W. and E.G. Beauchamp Availability of manure slurry ammonium for corn using N labeled (NH ) SO. Canad. J. Soil Sci. 7:. Shah, Z., R. Ullah and T. Hussain.. Can crop residue and glucose carbon stimulate dentrification and N mineralization in soil under submerged conditions? Pak. J. Soil Sci. (): 6. Shah, Z. and A.A. Khan.. Evaluation of crop residues for mineralizable nitrogen in soil. Sarhad J. Agric. 9(): 8-9. Shah, Z. and M. Anwar.. Assessment of municipal solid wastes for nutrient elements and heavy toxic metals. Pak. J. Soil Sci. ():-. Shah, Z., S. Roshan, A.U. Bhatti, and M. Afzal.. Chemical composition of municipal solid wastes of Peshawar city. Soil and Environ. (): SYSTAT Inc. 99. SYSTAT. for Windows, Evanston, IL, USA Thomas, G.W Soil ph and soil acidity. Pages 7-9. In Sparks, D.L. (ed.). Methods of Soil Analysis: Part. Chemical methods. Soil Sci. Soc. Amer. Book Series No.. SSSA and ASA, Inc., Madison, Wisconsin, USA Zaman, M. H. J. Di. and K. C. Cameron. 999b. Gross N mineralization and nitrification rates and their relationships to enzyme activities and soil microbial biomass in soils treated with dairy shed effluent and ammonium fertilizer in the field. Soil Use Mgt. : Zaman, M., H. J. Di, K. C.Cameron and C. M. Frampton. 999a. Gross N mineralization and nitrification rates and their relationships to enzyme activities and soil microbial biomass in soils treated with dairy shed effluent and ammonium fertilizer at different water potentials. Biol. Fert. Soils. 9: Zaman, M., H.J. Di, K. Sakamoto, S. Goto, H. Hayashi and K. Inubushi. a. Effects of sewage sludge compost and chemical fertilizer applications on microbial biomass and N mineralization rates. Soil Sci. Plant Nutr. 8 () 9. Zaman, M., K.C. Cameron, H.J. Di and K. Inubushi. b. Changes in mineral N, microbial biomass and enzyme activities in different soil depths after surface applications of dairy shed effluent and ammonium fertilizer. Nutrient Cycling in Agroecosystems Zaman, M., K.C. Cameron, H. J. Di and M. J. Noonan Nitrogen mineralization rates from soil amended with dairy pond waste. Aust. J. Soil Res. 6: 7.