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Burcu Tasatar, Koray Haktanır Soil Science Department, Faculty of Agriculture, Ankara University, Ankara ABSTRACT In this research, DUSA (Industrial Yarn Manufacturing) and SEKA (Paper and Cellulose Production) manufacturing (both are located in Izmit) Wastewater Treatment Plant sludge samples were used. And, these sludges' physical, chemical, and biological effects on agricultural soil, taken from İzmit Alikahya village were search. For this purpose, soil-sludge mixtures moisturized up to 70% of their water absorption capacity (maximum 0.5 % evaporation permitted) were prepared and kept at 28 °C for the period of five months. Waste sludge applied (control, 20, 40, 80, 160 t ha-1) soil samples were analyzed at 10 different incubation periods to determine nitrogen mineralization (NH4+-N and NO3--N), soil respiration (CO2 evolution), and urease enzyme activity. The physical and chemical properties of soil and sludges were analyzed before and after the mixing to find out if particular sludge sample at given rate had changed soils' physical and chemical properties. Then, positive changes were doubled checked to determine correct sludge dosage. Finally, all results were compared with statistical methods. Finding of the research have shown that in both soil-sludge mixtures, depending on sludge dosage rate, there were increase in organic matter, available phosphorus, electrical conductivity (EC) and cation exchange capacity (CEC); decrease in pH value; and, no noticeable change in other physical and chemical properties of soil-sludge mixtures. SEKA sludge sample was more effective than DUSA's sludge in total nitrogen. But, DUSA's sample was more effective in pH drop and in the increase of density, organic matter, electrical conductivity, available phosphorus and total phosphorus content. Ureas enzyme activity, one of the soil's biological properties, increased with sludge application rate and decreased with incubation time was more for SEKA sludge than DUSA. However, the amount of CO2 decreased in both sludge, but SEKA sludge had more CO2 evolution. When incubation period ended, there was rapid mineralization observed in both sludge samples. The amount of NH4+-N has increased with the dosage rate, and nitrification was strongly affected by incubation period (p<0.01). INTRODUCTION Disposal of municipal sewage sludge and effluents has recently received much publicity because of the increasing amounts of these wastes produce by urban and industrial activities. Due to growing concern over disposal of sewage sludge in the oceans and the high cost of incineration, land application and land filling are becoming more common. Currently about 60% of the sewage sludge produced in the U.K., amounting to 18 million tones annually is applied to agricultural soils as organic manure (Chander and Brookes, 1991). The application of dried sewage sludge and sludge effluents to agricultural land is becoming a wide spread practice because of the high content of organic and inorganic N, P and other plant nutrients in such sludges. Soil enzymes play an important role in the mineralization of organic substances and making nutrient ions available. Due to the reactions of urease and phosphates NH4+ and PO4- are made available to plants from organic substances in soils. (Reddy et al.1987). The percentages of sludge C and N mineralized in soil vary with the sludge type applied to the soil, as well as with the amount and the composition of the organic matter in the sludges (Hattori, 1988). Epstein et al. (1976) showed that laboratory incubations of soil with high rates of sewage sludge could cause an increase in cation exchange capacity (CEC). Respiration rate is the most widely used index of soil microbial activity. Enzyme assays in conjunction with respiration rate measurements can provide a clearer picture of the overall soil microbial population and its activity (Stroo and Jencks, 1985). The purpose of this research is to determine the effect of two different sewage sludges on soil nitrogen mineralization (NH4+-N and NO3--N), CO2 evolution, and urease enzyme activities in soil after 140 days incubation period. The physical and chemical properties of soil and sludges were analyzed before and after the mixing to find out if particular sludge sample at given rate had changed soils' physical and chemical properties. MATERIALS AND METHODS Soil and Sludge Description : The soil used was from Izmit-Alikahya Village (0-20 cm depth) . Sewage sludges from DUSA (Industrial Yarn Manufacturing) and SEKA (Paper and Cellulose Production) manufacturing plants' (both are located in Izmit) wastewater treatment plants. Experimental Design : The soil sample and sludge samples were stored on ice in transit, and sieved (2<mm) and stored at 4°C for no longer than 1 week before assay of NH4+-N and NO3--N at the beginning. The soil sample 400 cm 3 volume plastic pots were filled with 200 g of soil. Both sludge were air -dried and then added to the pots containing 200 g. soil at 5 rates equivalent to 0, 20, 40, 80, and 160 t ha-1 on a volume (107 ºC, oven dry) basis and soil and sludge in each pot were mixed well. No chemical fertilizer was added with these treatments. The incubation experiment was conducted using a randomized block design with 3 replications (3 pots) per treatment. Finally ground (<2mm) sludge was thoroughly mixed with sieved (<2mm) soil. The pots were placed in an incubator at 28 °C. Throughout the incubation period, water losses exceeding 10% of the initial values were compensated for by addition of distilled water. Sampling and Analysis : Samples were taken at 1, 7, 14, 28, 42, 56, 70, 105, and 140 days of the incubation period for the following analyses. For each sample, pH and electrical conductivity (EC) were measured in a 1:2.5 water extract (Richards, 1954); organic material by using modified Walkley-Black Method (Jackson, 1962); grain size distribution by Bouyoucos (1951); soil cation exchange capacity (CEC) was determined by saturation with ammonium acetate at pH 7 (Chapman, 1965); total phosphorus was determined by the Vanado Molybdate method (Kacar, 1996); the soil was extracted with 60% of HClO4 and the extract assayed for available phosphorus (atomic emission spectrophotometer) (Kacar,1990). The soil samples was analyzed for concentrations of water soluble Ca++ , Mg++ using EDTA titration method, Na+, K+ using flame photometer, CO3 -2, HCO3- using 0.01 H2SO4, Cl- using the titration with 0.01 N AgNO3, and SO4-2 using calculation method (Richards,1954). The soil was extracted with 1 N NH4OAc , pH 8.2; and extract assayed for Na+ and K+(flame photometer) and Ca and Mg (titration with 0.01 N EDTA) (Borekci, 1991). Total nitrogen was assessed using the Kjeldahl method, as specified by Bremner (1965). For NH4+-N and NO3--N, moist soil was placed in 150 ml Erlenmeyer flasks with 100ml of 2M KCl. Flasks were placed on a rotary shaker for 30 min and contents filtered through whatman filter paper No. 42. Soil extracts were used for the measurement of NH4+-N and NO3--N by steam distillation using MgO and Devarda's alloy (Bremner, 1965). CO2 evolution was determined according to the method of Isermayer (1952), Urease enzyme activity was measured by Hoffman and Teicher Method (1957). Seka and Dusa plants' sludges physical and chemical properties were determined like soil sample as you see above. Statistical analyses were evaluated by ANOVA and differences among the groups were separated by LSD (Duncan's multiple range test, P<0.01). RESULTS and DISCUSSION Some Physical and Chemical Properties of Soil-Sludge Mixtures : The physical and chemical characteristics of the sludges and soil are shown in Table 1. Some physical and chemical properties of soil amended with Dusa and Seka sludges changed after 140 days of incubation period. Table 2 presents the changes in pH, EC, CEC, total and available phosphate, organic matter, organic carbon, total nitrogen, and C/N rate. The changes are calculated as the difference between the measured parameter for before treatments were applied and after 140 days treatments were applied. In both sludges used in the present study was approximately neutral, so in the soil, pH was decreased by the highest Dusa sludge treatment and Seka's 20, 40 treatments.  In Seka sludge applied pots pH was measured between 7.60 to 7.65 and Dusa sludge applied pots pH was measured between 6.81 to 7.77. EC increased with sludge additions for both sludge because of the higher salt content of both sludges. Sewage sludges increased CEC in each sludge soil mixures after incubation period. Increasing CEC was evident for soil that had been incubated in the laboratory, especially in the 15 to 30-cm depth samples. This is probably due to the slight increase in organic carbon (Cavallaro et al.1993). Epstein et al. (1976) reported that sewage sludge increased CEC as estimated by the sum of exchangeable cations or "effective CEC." After 140 days of incubation period available P was high at the beginning of the incubation period. Increasing P availability has been associated with sewage sludge and other organic amendments (Barbarick and Workman 1987; McCoy et al. 1986). Organic matter content significantly (p<0.01) increased with application of the highest dosage of Dusa sludge compare to Seka sludge. There is no significant difference in total nitrogen content after incubation period.  Some Biological Properties of Soil-Sludge Mixtures : Enzyme activities are generally considered to be a more direct expression of soil biological activity or of the activities of specific processes of nutrient cycling and organic matter turnover, than measurements of microbial numbers (Hattori, 1988). The changes in the activities of urease enzyme in the soil amended with Dusa and Seka sludges at 5 rates equivalent to 0, 20, 40, 80, and 160 t ha -1 are shown in Table 3. Table 3 shows that soil urease activity was significantly (p<0.01) changed after application of different doses of two sewage sludges during incubation period. Urease enzyme activity in soil amended with Seka sludge. Before sludge application soil urease enzyme activity was found 16.97 mg N 100 g-1. Urease enzyme activity changed in soil amended with Seka sludge between 17.51 to 35.45 mg N 100 g-1 in the first day of incubation period. In Dusa sludge, urease activity changed between 27.33 to 54.30 mg N 100 g-1 depend on the application doses in the first day. Soil urease enzyme activity values decreased to 23.83 to 19.60 mg N 100 g-1 in Dusa sludge and 15.29 to 18.57 mg N 100 g-1 in Seka sludge depend on the sludge application doses and incubation time during the incubation period. These values was found significantly (p<0.01) important according to variance analysis. Hoffman and Hofmann (1966) classified soil urease activity levels low (>8), normal (between 8-16), and high (16<). Dusa sludge effected on soil urease enzyme activity more than Seka sludge in 160 t ha -1 dosage rate in first, 7, 28, 42,and 56 days of incubation. This result was found significantly (p<0.01) important depend on variance analysis. Dusa and Seka sludges effected soil urease enzyme activity differently. In all treatments sludge rates increased urease enzyme activity but urease enzyme activity decreased depend on incubation period in amended soil with both sludges.  Before sludge application, CO2 evolution was found 3.15 mg CO2 /100 g 24 hour in soil. In the first day of the incubation period CO2 evolution was found between 2.04 to 6.47 mg CO2/100 g.24 hour in soil amended with Dusa sludge and between 2.98 to 6.40 mg CO2/100 g.24 hour in soil amended with Seka sludge. CO2 evolution increased until 7th day of incubation period depend on sludge dosage incerease. Following incubation times, CO2 evolution decreased in soil amended with both Dusa and Seka sludges depend on doses and incubation period. CO2 evolution that is a result of soil microbial activity and soil organic matter decomposition decreased depend on application doses and increasing time. CO2 evolution decreases especially in higher rates doses during incubation period this shows inhibition of general-purpose microorganisms in soil (Diaz-Burgos et al.,1993). In all treatments Seka sludge increased CO2 evolution more than Dusa sludge and this was found significantly (p<0.01) important as a result of variance analysis.  The changes in the amount of NH+4-N in the soil amended with Dusa and Seka sludges at 5 rates equivalent to 0, 20, 40, 80, and 160 t ha -1 are shown in Table 5. First day of the incubation, the amount of NH+4-N was found between 160.53 to 270.67 mg kg-1 in soil amended with Dusa sludge and between 164.97 to 206.50 mg kg-1 in soil amended with Seka sludge. The amount of NH+4-N decreased depend on the time but it is increased depend on the increasing sludge application doses. In the research, between amonification and time and doses were found significant (p<0.01) relations. Sozudogru et al. (1996), was found quicker amonification in the first and second weeks of incubation and than amonification decreased step by step during incubation period. At the end of the incubation period all left NH+4-N (mg kg-1) amounts approached each other. (Dusa sludge 33.33-46.33 mg kg-1, Seka sludge 42.70-50.23 mg kg-1). Quick mineralization can explain with higher Nitrate content (3.26%) and narrow C/N rate (10.47) in the soil amended with Dusa sludge. Slow mineralization can explain with lower Nitrate content (1.14%) and wider C/N rate (21.38) in the soil amended with Seka sludge. There is no different effects of both sludges was found over soil's NH+4-N content except 160 t ha-1 application rate. Dusa sludge showed higher mineralization than Seka sludge in the 160 t ha-1 application rate.  The first day of the incubation, the amount of NO3--N was found between 203.50 to 285.00 mg kg-1 in soil amended with Dusa sludge and between 140.30 to 247.60 mg kg-1 in soil amended with Seka sludge. In soil samples amended with Dusa sludge, nitrification increased the highest level and was observed significant differences between doses in six weeks that is following amonification. Table 6 shows that NO3--N amount was significantly (p<0.01) changed depend on dosage rates and incubation period. In soil samples amended with Seka sludge, NH+4-N and NO3--N amounts were found lower than Dusa's samples but there is more homogeneity in mineralization dispersion. Sozudogru et al. (1996) was found similar results in their incubation research.  In all treatments Dusa sludge significantly (p<0.01) showed higher nitrification rate than Seka sludge. Seka and Dusa sludges effected amended soil positively. Dusa sludges had higher plant nutrient matter than Seka sludges. When Dusa sludge was applied to soil it increased soil biological activity rapidly. Both sludges can use as a soil improver or soil fertilizer without any inhibition in the soil if their metal content and trace element content were known. ACKNOWLEDGEMENTS This PhD thesis has been supported by TUBITAK through contract No: TOGTAG-1472. REFERENCES Barbarick, K .A., S.M. Workman. (1987). Ammonium bicarbonate-DTPA and DTPA extractions of sewage sludge amended soils.J.Environ.Qual.16:125-130. Bouyoucus, G.O.A. (1951). Recalibration of the hidrometer method for making mechanical analysis of soils. Agronomy Journal, 43, 434-438. Börekçi, M. (1991). Türkiye topraklarında katyon değişim kapasitesi ile değişebilir katyonların tayininde uygulanacak metodlar, T.C. Tarım ve Köyişleri Bakanlığı, Köy Hizmetleri Genel Müdürlüğü, Toprak ve Gübre Araştırma Enstitüsü Müdürlüğü, 174, Ankara, 37-40. Bremner, J.M. (1965). Methods of soil analysis, Part 2, Chemical and Microbiological Properties, Ed. C.A. Black, Amer. Soc. of Agron.Inc.Pub.Agron.Series No:9, Madison, Wisconsin, USA. Cavallaro, N., N.Padilla, , J. Villarrubia, (1993). Sewage sludge effects on chemical properties of acid soils. Soil Science, 156, 2, 63-70. Chapman, H.D. (1965). Methods of soil analysis Part 2. Chemical microbiological properties. Ed. C.A. Black. Amer. Soc. Of Agron. Inc. Publ. Agron. Series no: 9, Medison, Wis, USA. Chander,K., P.C.Brookes.1991. Effects of heavy metals from past applications of sewagw sludge on microbial biomass and organic matter accumulation in a sandy loam and silty loam U.K. soil. Soil Biol.Biochem.Vol.23, No.10:927-932. De Boodt, M., , O.Verdonck, I. Cappaert. (1973). Method or measuring the water release curve of organic substrates. Proceeding Symposium Artificial Media in Horticulture. 2054-2062. DIiaz-Burgos, A., B. Ceccanti, A. Polo. (1993). Monitoring biochemical activity during sewage sludge composting. Biology and Fertility of Soils. 16:145-150. 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Stroo, H.F., E.M. Jencks . (1985). Effect of Sewage Sludge on Microbial Activity in an Old, Abondoned Mineral soil. J. Environ. Qual., V.14, 3:301-304. |