Plant and animal residue decomposition and transformation of S and P in soil

Microbial respiration (C02 evolution), inorganic SO4-S and available P were monitored in a S deficient soil amended with dhaincha, cowdung and rice straw at a rate of 1 g per 50 g soil during 30 days incubation. A basal dose of 250 mug N, 200 mug P and 250 mug K g-1 soil was applied. Dhaincha showed the highest decomposition rate and rice straw showed the lowest rate, while that of cowdung was intermediate. After 30 days of incubation, 53, 17 and 39% C was decomposed from cowdung, rice straw and dhaincha, respectively. Decomposition was also found to be related to its nutrient status (C:N:S ratio). Considerable S mineralization was recorded in dhaincha and cowdung amended soil and attained the maximum at 15th day (13.8 mug g-1 S) and 30 (9.8 mug g-1 S), respectively. During rice straw decomposition S was immobilized markedly. Application of plant and animal residues caused significant increase in P mineralization. Net mineralization was 95.5, 87.6 and 50.8 mug P g-1 soil in dhaincha, cowdung and rice straw amended soil, respectively.