Layer Chicken Parent Stock Pelleted Litter as Fertilizer in Soybean Production

137 (1): 53-60, June 2008 ISSN 0031-7683 Layer Chicken Parent Stock Pelleted Litter as Fertilizer in Tawadchai Suppadit 1*, Laongdown Sangla 2 and Ladda Udompon 3 1 The Graduate Program in Environmental Management, School of Social and Envmtl Dvlpmt National Institute of Development Administration Bangkapi, Bangkok, Thailand 2 Chiang Mai Field Crops Research Center, Office of Agrl Research and Dvlpmt, Region 1 Department of Agriculture, Ministry of Agriculture and Cooperatives Sansai, Chiang Mai, Thailand 3 Sanitation and Health Impact Assessment Division, Department of Health Ministry of Public Health, Muang, Nonthaburi, Thailand Alternative waste management practices need to enhance the safe and economical production of layer chicken parent stock. An appropriate method to enhance safety and benefit is to reuse layer chicken parent stock litter as fertilizer for soybean production. Research was done to study the growth of soybeans, lipid, and protein content in seeds, and heavy metal content in leaves and seeds after the experiment. The experiment was conducted at an artificial housing constructed in Muang district, Ratchaburi province, Thailand from May to September, 2006. The research comprised 6 treatments: pelleted layer chicken parent stock litter (PLCPSL) at rates of 0, 0.02, 0.04, 0.06, 0.08 kg/pot mixture and chemical fertilizer (12 24 12) at a rate of 0.01 kg/pot were provided to soybean cultivar Chiang Mai 60 (CM. 60). Results showed that PLCPSL could be used as fertilizer for soybean production with an optimum rate of 0.08 kg/pot mixture, which gave the best performance in terms of the number of nodes, height, dry matter accumulation, and total yield, exceeding the results obtained from using chemical fertilizer. Also, the nutrient content in the soil after the experiment increased as the PLCPSL content increased. Seed protein showed the highest level when using PLCPSL at a rate of 0.08 kg/pot, whereas seed lipids showed the lowest content. After the experiment, the heavy metal content (lead, cadmium, and mercury) in the leaves was higher than standard values. Key Words: fertilizer, heavy metal, layer chicken, litter, nutrient, soybean INTRODUCTION Layer chicken raising is an important livestock industry in Thailand. In 2005, the total number of layer chickens was 41,210 [Department of Livestock Development (DLD) 2006] and this number increased by 0.478% annually from 2001 2005. The increasing number of layer chickens has led to an increase in the raising of layer chicken parent stocks. In 2004, *Corresponding author: tawatc.s@nida.nida.ac.th stawadchai@hotmail.com Thailand imported 669,305 layer chicken parent stocks (DLD 2005). The expansion in the rearing of layer chicken parent stock has had a negative impact on the environment due to some significant residual wastes, such as the litter (rice husk-based) (Suppadit 2007). If not treated correctly litter produces a foul odor which affects the environment negatively. The litter can also become a source of disease pathogens and produce poisonous gases from fermentation. When the litter is washed away into a surface water source, it 53

increases nutrients for water plants. Water plants that grow in abundance eventually reduce oxygen in the water and negatively affect aquatic animals (Suppadit 2002). However, if the litter is properly handled, it can become fertilizer for crop production. A study by Udompon (2006) revealed that fertilizer made from the litter of layer chicken parent stock has higher nutrient content than broiler litter (2.9% N, 1.6% P and 2.3% K) (Suppadit 2000), with nitrogen (N), phosphorus (P), and potassium (K) levels of 3.7, 4.9, and 2.35%, by weight, respectively. However, the process of transforming the litter of layer chicken parent stock into fertilizer is rather complicated. There are also problems with flies, dust, and smell. One acceptable method to solve this problem is pelleting. In their experiment, Suppadit et al. (2002) had the litter of layer chicken parent stock undergo a pelleting process with satisfactory result. The pelleting process created a temperature of 90 C and consequently reduced environmental pollution. Both the environmental problems and the potential usefulness of the litter of layer chicken parent stock are the motives behind this study on pelleted litter of layer chicken parent stock to produce fertilizer for soybeans, a crucial cash crop in Thailand (Suppadit 2000). This practice is expected to increase the income of farmers who raise layer chicken parent stock and reduce soybean production costs, because the litter-based fertilizer from this source can replace chemical fertilizer. MATERIALS AND METHODS Pelleted Layer Chicken Parent Stock Litter (PLCPSL) Preparation Layer chicken parent stock farms were randomly chosen from among those located in Saraburi province, Thailand. The PLCPSL was modified and pelleted through the method used in the study by Suppadit et al. (2002). The pelleting process produced temperatures up to 90 C and the pellet size was 6 mm in diameter and 2 cm in length. The chemical characteristics, nutrients and heavy metals in the PLCPSL after analysis were 9.81 mmhos/cm electrical conductivity (EC), ph 7.5, 38.5% organic matter (OM), 2.39% nitrogen (N), 76,600 mg/kg phosphorus (P), 44,800 mg/kg potassium (K), 135,200 mg/kg calcium (Ca), 5,300 mg/kg magnesium (Mg), 4,500 mg/kg iron (Fe), 900 mg/kg zinc (Zn), 140 mg/kg copper (Cu), 690 mg/kg manganese (Mn), 13.2% moisture, 9:1 C:N ratio, 46.4 mg/kg lead (Pb), 14.1 mg/ kg cadmium (Cd), and 1.7 mg/kg mercury (Hg). Experiment location Trials were conducted at Muang district, Ratchaburi province from May to September 2006. The trials were done in an artificial greenhouse that measured 6 m wide x 8 m long x 2 m high (96 m 3 ) under a plastic roof. Corrugated iron and blue netting were used as border around the greenhouse. The black plastic pots in which the soybeans were planted were 28 cm wide (616 cm 2 ) x 22.5 cm high. Experimental design This study was a completely randomized design with 4 separate replications (Gomez & Gomez 1984). The treatments were as follows: T0: Control (without PLCPSL or chemical fertilizer). The initial nutrient analysis showed 5,700 mg N, 50 mg P, and 380 mg K. T1: Soil (9.98 kg) mixed with PLCPSL (0.02 kg) per pot. The initial nutrient analysis showed 6,167 mg N, 1,581 mg P, and 1,275 mg K. T2: Soil (9.96 kg) mixed with PLCPSL (0.04 kg) per pot. The initial nutrient analysis showed 6,633 mg N, 3,114 mg P, and 2,170 mg K. T3: Soil (9.94 kg) mixed with PLCPSL (0.06 kg) per pot. The initial nutrient analysis showed 7,100 mg N, 4,646 mg P, and 3,066 mg K. T4: Soil (9.92 kg) mixed with PLCPSL (0.08 kg) per pot. The initial nutrient analysis showed 7,566 mg N, 6,178 mg P, and 3,961 mg K. T5: Chemical fertilizer formula 12 24 12 (1 2 1), 0.01 kg/pot, applied 20 days after emergence following suggestions issued by the CMFCRC (2002). The initial nutrient analysis showed 6,900 mg N, 2,450 mg P, and 1,580 mg K. The soybean cultivar Chiang Mai 60 (CM. 60) was used for the evaluation. Soil from the Ratchaburi soil group, Muang district, Ratchaburi province was used and mixed with PLCPSL for a total weight of 10 kg/ pot (T1 T4). The soil weight of T0 and T5 was 10 kg/ pot, and was not mixed with PLCPSL. After two wk, soybean seeds were inoculated with Rhizobium spp. for N fixation and planted in each plastic pot, then thinned one wk after emergence, leaving four seedlings per pot. These were watered until the R7 stage (beginning maturity). The entire plot area was weeded by hand. Tobacco was used for insect control. Data recorded were planting date, stage of emergence, number of nodes, height, leaf area, dry matter, yield (4 plants/ pot x pods/plant x seeds/pod x 1 seed weight), number 54

of pods/plant, number of seeds/pod and dry weight of 100 seeds. Seed germination and vigor of harvested seeds were recorded based on ISTA Rules (1985). Protein and lipids were measured using the Kjeldahl method with a Kjel Foss Automatic (Model 16210) and by Soxhlet Extraction method, respectively. Heavy metals in plant composition were measured using the methods of atomic direct aspiration for Pb and Cd and atomic absorption cold vapor for Hg with an Atomic Absorption Spectrophotometer (AAS). Heavy metals and macro- and micro-nutrients in the PLCPSL and soil were measured using the method of inductively coupled plasma atomic emission with an Inductively Coupled Plasma Emission Spectrophotometer. PLCPSL and soil chemical characteristics in terms of EC (Electrical Conductivity method), ph (ph Meter), and OM (Walkley Black method) before and after the experiment were analyzed based on the Occupational Health Division (1986) s Manual. Data were analyzed through an analysis of variance (ANOVA). When significant differences were observed, the Duncan s New Multiple Range Test (DNMRT) of the Statistical Analysis System (SAS version 6.12) was used to test for differences among the treatment means at a significance level of p<0.05 (SAS Institute 1996). RESULTS AND DISCUSSION Potential growth and yield The number of soybean nodes and soybean height at stage R8 (full maturity) was significant for all treatments (p<0.05) (Figure 1). Increasing the content of the PLCPSL corresponded to a slight increase in the number of nodes and plant height, which could be due to the increase in nutrients for soybean growth. The highest node/plant of 9 nodes and the tallest height of 101 cm were obtained from 0.08 kg/pot mixture (T4) while the lowest node/plant of 6.75 nodes and the shortest height of 83.8 cm were obtained from the 0 kg/pot mixture (T0). This is lower than values obtained in studies by Srisomboon (1999) and Chaiyo (2005), which reported 14.5 nodes/plant and heights of 90 102 cm. The soybean leaf areas were significant for all treatments (p<0.05), except for the R7 stage (Figure 2). At the reproductive growth stage (Fehr and Caviness 1977) of R1 (beginning bloom; 714 cm 2 /2 plants) and R3 (beginning pod; 799 cm 2 /2 plants), the chemical fertilizer treatment (T5) showed the highest value of leaf areas because of the effects of the fertilizer application (applied at 20 days after emergence). Nevertheless, at the R5 stage (beginning seed; 866 cm 2 /2 plants), the PLCPSL rate of 0.08 kg/pot mixture (T4) showed the highest value. As the soybean Node (number) 10 9 8 7 6 5 4 3 2 1 0 T0 T1 T2 T3 T4 T5 Treatment Height (cm) 120 p<0.05 p<0.05 100 80 60 40 20 0 Node Height Figure 1. Number of main stem nodes and height of soybean cultivar CM. 60 at different levels of PLCPSL and chemical fertilizer 55

cm 2 /2 plants 1000 P<0.05 900 P<0.05 800 P<0.05 700 600 500 400 300 200 100 0 R1 R3 R5 R7 Growth stage T0 T1 T2 T3 T4 T5 Figure 2. Leaf area of soybean cultivar CM. 60 at different levels of PLCPSL and chemical fertilizer Not significantly different g/plant 7 6 5 4 3 2 P<0.05 P<0.05 T0 T1 T2 T3 T4 T5 1 0 R1 R3 R5 R6 R7 R8 Growth stage Figure 3. Dry matter of soybean cultivar CM. 60 at different levels of PLCPSL and chemical fertilizer Not significantly different leaf area increased from the R1 stage to R5 stage, the data showed that increasing the PLCPSL content corresponded to an increase in the leaf area. Therefore, the 0.08 kg/ pot mixture (T4) was also the optimum rate for soybean production. This result agrees with that of Suppadit et al. (2005a), who reported that the soybean leaf area increased with the content of shrimp excrement mixed with the soil at a rate of 8% by weight (0.08 kg/pot). 56

Dry matter production differed significantly for all treatments only at stages R1 and R3 (p<0.05) (Figure 3). However, dry matter accumulation at stages R5, R6 (full seed), R7, and R8 did not differ (p>0.05). The rate of 0.08 kg/pot mixture (T4) showed the highest dry matter at stages R7 and R8 with 6.37 and 6.1 g/plant, respectively. In the early stages (R1 and R3 stages), dry matter accumulation was highest in the chemical fertilizer treatment (T5), and was higher than the 0.08 kg/pot mixture treatment (T4) because the chemical fertilizer could be absorbed by the plants immediately. The dry matter accumulation in all treatments had the highest levels at stage R7 and slightly decreased at stage R8. Contrasting results were reported by Chaiyo (2005), who found dry matter accumulation was greatest at stage R8. However, similar results were obtained by Hanway & Thomson (1967), who reported that leaf and stem dry matter were accumulated at an early stage (R7), and then decreased at the pod development and the seed filling stage. Meanwhile, pod and seed dry matter accumulated when carbohydrates were moved from sources (leaf and stem) to sinks (pod and seed) at the final stage. Moreover, Hanway & Weber (1971) reported that the stem dry matter accumulation of soybeans showed the highest value about 15 days after the flowering stage and had a lower value at the full maturity stage. They concluded that carbohydrates were also moved from the stems to the seeds to meet the growth demands for seed development. Yield (4 plants/pot) differed significantly for all treatments (p<0.05) (Table 1), with the highest yield of 22.5 g/pot coming from the 0.08 kg/pot mixture (T4) and the lowest yield of 5.51 g/pot from the 0 kg/pot mixture (T0). Increasing the content of PLCPSL corresponded to an increase in soybean yield. Furthermore, the Chiang Mai Field Crops Research Center (CMFCRC) (2002) has reported that plant yield is influenced by the yield components. This study showed that the highest yielding treatment, T4, resulted from high values for pod/plant, Table 1. Yield and yield components of soybean cultivar CM. 60 at different levels of PLCPSL and chemical fertilizer Treatment T0 T1 T2 T3 T4 T5 Yield (g/pot) 5.51 f 10.3 e 15.2 d 18.4 b 22.5 a 16 c Pods/plant (pod) 6 b 8.5 b 11.8 a 13 a 14.8 a 12.8 a Yield component Seeds/pod (seed) 1.8 b 1.83 b 1.91 ab 2.02 ab 2.14 a 1.94 ab 100 seeds dry weight (g) 10.7 d 12.2 c 12.5 c 13.8 b 15 a 13.4 b CV 3.01 19.3 9.3 4.1 Means in the same column with different superscripts are significantly different at p<0.05. seed/pod and 100 seed dry weight. Pataradilok (1991) reported that the yield/plant of soybean cultivar CM 60 planted in March was 12.5 g/plant, considerably more than all of the treatments in the present study. The number of soybean pods was significant for all treatments (p<0.05) (Table 1). Increasing the content of PLCPSL produced more pods/plant. The highest number of pods/plant was reported for the 0.08 kg/pot mixture (T4) (14.8 pods/plant), whereas the 0 kg/pot mixture (T0) had the lowest number (6 pods/plant). Contrasting results were obtained by Chaiyo (2005), who reported 16.5, and Kaewmeechai (1994), who reported 50 70 pods/plant. The number of seeds/pod was significant for all treatments (p<0.05) (Table 1), with the highest value of 2.14 seeds/pod for the 0.08 kg/pot mixture (T4), while the 0.02 (T1) and 0 kg/pot mixture (T0) had the lowest value of 1.83 and 1.8 seeds/pod, respectively. Similar results were obtained by Kaewmeechai (1994), who reported that the standard number of seeds/pod for soybean cultivar CM 60 is 2 3 seeds/pod. The 100 seeds dry weight was significant for all treatments (p<0.05) (Table 1). Increasing the content of PLCPSL corresponded to an increase in seed weight. The results varied similarly to soybean pod number per plant. The 0.08 kg/pot mixture (T4) showed the highest 100 seeds dry weight of 15 g, whereas the 0 kg/pot mixture (T0) had the lowest dry weight of 10.7 g. These figures are slightly low when compared with Kaewmeechai (1994), who reported a seed weight of 15 17 g. Seed quality The effect of PLCPSL treatments on seed germination and vigor was significant (p<0.05) (Table 2), with the highest values of 50.4 and 41.9% for the 0.08 kg/pot mixture (T4). The 0 kg/pot mixture (T0) showed the lowest values of 32.2% and 29.5%, respectively. Increasing the content of PLCPSL generally increased the percentage seed of germination and vigor. These figures were much lower than Table 2. Seed quality, protein and lipid content of soybean cultivar CM. 60 at different levels of PLCPSL and chemical fertilizer Treatment T0 T1 T2 T3 T4 T5 Germination 32.2 d 38.7 c 44 b 47.1 b 50.4 a 41.8 c Vigor 29.5 d 34.6 c 37.4 b 39.2 ab 41.9 a 38 b Protein 33 e 33.5 de 34.1 cd 36.3 b 37.1 a 34.7 c Lipid 20.8 a 20.6 a 20.6 a 19.8 b 19.6 b 20.2 ab CV 6.08 5.48 1.3 2.5 Means in the same column with different superscripts are significantly different at p<0.05. 57

Sangla (2004) who reported that soybean seed germination and vigor should be higher than 80%. The level of seed protein of all treatments was significant (p<0.05) (Table 2). The 0.08 kg/pot mixture (T4) showed the highest value of 37.1%, whereas the 0 kg/ pot mixture (T0) had the lowest value of 33%. Increasing the content of PLCPSL related to an increase in seed protein content. All treatments were less than the 43.8% obtained by Kaewmeechai (1994). Seed lipid content was also significant for all treatments (p<0.05) (Table 2). Increasing the content of PLCPSL above the T3 rate of 0.06 kg/pot corresponded to a decrease in seed lipid content, because lipid content is inversely related to protein content. Therefore, the 0.08 kg/pot mixture (T4) showed the lowest value of 19.6%, whereas the 0 kg/pot mixture (T0) had the highest value of 20.8%. Similar results were obtained by the CMFCRC (2000), which reported an average lipid content of 20% for soybean cultivar CM 60 in experimental fields of the Sansai soil group. Heavy metal content in mixed soil After mixing the soil with the PLCPSL, the content of each heavy metal was 4.1 mg/kg Pb, 4.9 mg/kg Cd, and 1.7 mg/ kg Hg for all treatments. After the experiment (Table 3), the level of Pb in mixed soil differed significantly for all treatments (p<0.05), and ranged from 0.4 to 1.36 mg/kg. The 0.08 kg/pot mixture (T4) had the highest Pb content. Cd was also significant for all treatments (p<0.05). The 0.08 (T4) and 0.06 (T3) kg/pot mixture had the highest Cd content of 3.76 and 3.35 mg/kg, respectively. The lowest value was for the 0.02 (T1) and 0 (T0) kg/pot mixtures, with levels of 0.55 and 0.76 mg/kg, respectively. Hg was not significant for all treatments (p>0.05), and the values obtained ranged from 0.0782 0.0858 mg/kg. Increasing the content of PLCPSL corresponded to an increase in Pb and Cd. Heavy metal content decreased continuously after the experiment due to adsorption or fixation by the soil, microorganism activity, leaching, and soybean absorption. Although their contents before experiment were above standard levels, their contents after the experiment were not, except Cd (the standard mean averages are Pb: 0.1 30; Cd: 0.1 2; and Hg: 0.1 1 mg/kg), as reported by Panichasakpatana (1996). Heavy metal content in leaves The values for leaf Pb, Cd, and Hg were significant for all treatments (p<0.05), and ranged from 3.5 to 34.3, 3.2 to 15.3, and 0.0184 to 0.426 mg/kg, respectively. The 0.08 kg/pot mixture (T4) showed the highest values of Pb, Cd, and Hg of 34.3, 15.3, and 0.426 mg/kg, respectively, whereas the 0 kg/pot mixture (T0) had the lowest values of 3.5, 3.2 and 0.0184 mg/kg, respectively. Increasing the content of PLCPSL corresponded to an increase of Pb and Hg accumulation in leaves due to a high concentration of heavy metals in PLCPSL. Sirisukhodom (1992) and Panichasakpatana (1996) reported that standard ranges in plants are Pb: 0.5 3, Cd: 0.1 1 and Hg: 0.001 0.01 mg/ kg. The contents observed in this study were considerably higher than these standard levels. Heavy metal content in seeds The concentrations of Pb, Cd, and Hg in the seeds ranged from 0.96 to 27.6, 0.0223 to 0.045, and 0.0009 to 0.0056 mg/kg, respectively. These values were significantly different among treatments (p<0.05), except for Cd (Table 3). The 0.08 kg/pot mixture (T4) showed the highest values of Pb, Cd and Hg (27.6, 0.045 and 0.0056 mg/ kg). Only the Pb content exceeded standard levels for all treatments when compared with the results obtained by Panichasakpatana (1996). The accumulation of heavy metals in the seeds was lower than that in the leaves. These results were similar to Chaiyo (2005), who reported that there was less accumulation of Pb, Cd, and Hg in seeds because leaves generally had more time than seeds to absorb heavy metals. Also, the results of Suppadit et al. (2005b) revealed that heavy metals in leaves and seeds Table 3. Heavy metals in soil after experiment, soybean leaf (R5), and soybean seed (R8) Treatments Soil after experiment * Soybean leaf Soybean seed Pb Cd Hg Pb Cd Hg Pb Cd Hg To 0.4 c 0.55 c 0.0782 3.5 f 3.2 c 0.0184 e 0.96 c 0.0223 0.0009 b T1 0.93 b 0.76 c 0.0824 18 d 14.1 b 0.0655d 14.2 b 0.036 0.0018 b T2 0.97 ab 2.06 b 0.0844 20 c 14.3 b 0.197 c 16.7 b 0.038 0.0024 b T3 1.08 ab 3.35 a 0.0853 24.6 b 14.5 b 0.347 b 16.9 b 0.04 0.0047 a T4 1.36 a 3.76 a 0.0858 34.3 a 15.3 a 0.426a 27.6 a 0.045 0.0056 a T5 0.9 b 2.05 b 0.0844 12.4 e 13.9 b 0.0546d 15.8 b 0.039 0.0045 a CV 26.6 19.8 22.2 2.58 2.83 20.2 11.3 19.5 27.4 Means in the same column with different superscripts are significantly different at p<0.05. * Ratchaburi soil group of all treatments was sampled from natural planting areas, and always contained a quantity of heavy metals. Not significantly different. 58

Table 4. Chemical characteristics and nutrients in soil after experiment Treatments EC (mmhos/cm) ph OM N P K Ca Mg Fe Zn Cu Mn T0 1.34 c 7.9 a 1.06 d 0.049 b 7.96 e 43.6 f 2,589 b 899 e 5.88 b 0.291 d 0.219 d 22.9 e T1 1.36 c 7.2 b 1.29 cd 0.065 b 89.1 d 166 d 26,200 a 1,078 c 6.10 b 0.702 cd 0.714 cd 43.3 c T2 1.8 b 7.08 b 1.46 c 0.073 ab 91.3 c 212 c 28,490 a 1,083 c 6.50 b 1.11 c 0.933 bc 44.2 c T3 1.97 b 7.34 b 1.84 b 0.093 ab 139 b 285 b 29,150 a 1,231 b 6.52 b 2.40 b 1.37 b 74.2 b T4 3.23 a 7.32 b 2.21 a 0.111 a 163 a 410 a 29,850 a 1,695 a 12.6 a 3.99 a 2.05 a 103 a T5 3.34 a 6.87 b 0.99 d 0.053 b 80.5 d 99.4 e 26,850 a 996 d 6.37 b 0.461 d 0.708 cd 32.8 d CV 10.6 4.91 15.4 18.5 10.9 3.23 11.4 4.39 19.5 24.8 17.4 4.94 Means in the same column with different superscripts are significantly different at p<0.05. affected soybean yield potential and yield components as they stunted the growth of sensitive plants. Moreover, heavy metal toxicity in plants depends on soil fertility. Plants grown in fertile soil can tolerate heavy metal toxicity better than plants grown in infertile soil. Chemical characteristics and nutrients Table 4 shows soil chemical characteristics and nutrients after the experiment. Before the experiment, the EC was 1.43 mmhos/cm for all treatments; after the experiment it increased because of the content of the PLCPSL. Therefore, these values were significant for all treatments (p<0.05). The chemical fertilizer (T5) and the 0.08 kg/pot mixture (T4) showed the highest EC values (3.34 and 3.23 mmhos/ cm), respectively, while the lowest values were for the 0.02 (T1) and 0 kg/pot mixtures (T0) with values of 1.36 and 1.34 mmhos/cm, respectively. The results for the 0.08 kg/ pot mixture (T4) and chemical fertilizer (T5) were higher than the standard values for plants (<2 mmhos/cm). Soil ph before the experiment was 7.5 for all treatments. After the experiment, the ph values were significant for all treatments (p<0.05), ranging from 6.87 7.9. The optimum soil ph for soybean production is 6.5 7, as reported by the CMFCRC (2002). After the experiment, basically all treatments tended to have a lower soil ph, because the soil had moisture and organic matter, and later organic acids (fulvic acid and humic acid) and carbonic acid may have been created from organic degradation activities (Osotsapar 2002). Before the experiment, soil nutrients OM, N, P, K, Ca, Mg, Fe, Zn, Cu, and Mn were 1.14%, 0.057%, 5 mg/kg, 38 mg/kg, 2,226 mg/kg, 841 mg/kg, 4.09 mg/kg, 0.13 mg/kg, 0.53 mg/kg, and 13.4 mg/kg, respectively, for all treatments. After the experiment, however, these values were significant for all treatments (p<0.05), except Ca, with the highest contents obtained for the 0.08 kg/pot mixture (T4). The 0 kg/pot mixture (T0) had the lowest content of N, P, K, Ca, Mg, Fe, Zn, Cu, and Mn. For organic matter, the chemical fertilizer (T5) and 0 kg/pot mixture (T0) showed the lowest content. Soybean growth in T5 was greater than in T0 and, as a result, there was greater amount of residual roots that decomposed in the soil. Thus, soil Ca, Mg, Mn, Pb, and Cd concentrations were significantly greater in T5 as compared to T0. CONCLUSION Increasing the content of PLCPSL corresponded to an increase in soil nutrients and soil fertility. The growth and yield of soybeans responded to PLCPSL application. Application of PLCPSL at 0.08 kg mixture (T4) contributed to the best soybean growth and potential productivity, and was better than using 0.01 kg of chemical fertilizer. However, the productive performance of all treatments was lower than those obtained from other studies and actual fields, which may result from the environmental conditions including cultivar, pot conditions, soil characteristics such as ph, EC and heavy metals, climate, light concentration and planting season. PLCPSL can be used as a replacement nutrient source for chemical fertilizer in soybean production. However, PLCPSL contains higher amounts of heavy metals than other manures such as broiler litter. Heavy metals may be a concern for food and environmental safety because some heavy metal levels observed after the experiment in soils, leaves, and seeds were considerably higher than the standard levels. ACKNOWLEDGEMENTS The author would like to thank the Siriwan Company Limited for the pelleting and funding, and the Department of Agriculture, Ministry of Agriculture and Cooperatives, and Kasetsart University for materials and laboratory support. 59

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