Abstract
The decomposition of organic materials in Dark Red Soil under field conditions was measured using a glass-fiber filterpaper method. The samples examined were seven green menure (sorghum, pigeon pea, sesbania, guinca grass, pampas grass, clotararia, oats) and four composts prepared from bagas, poultry manure, cattle feces and sugarcane leaves. The order in the total carbon decomposition rate of organic materials after 3 y was green manure > poultry manure ≒ bagas > manure made from sugarcane leaves ≒ cattle feces. Three mathematical models were examined to compare the fitness of the decomposition values, and the following double-compartment first-order kinetics model was the best among the models : D_t = C_1e^<-k1t> + C_2e^<-k2t> (C_1 +C_2 =100%), where D_t is the amount of residual carbon of organic materials at time t (month) and C_1 (labile fraction) and C_2 (non-labile fraction) are the initial proportions decomposed according to the rate constants k_1 and k_2, respectively. The C_1 value was positively correlated with the total carbon of the organic material, the amount of ethanol-benzene soluble fraction and the amount fo hot water plus ethaanol-benzene solible fraction. The C_2 value was positively correlated with the amount of lignin. Using the decomposition rate obtained by this model, the long-term changes in total carbon in the soil by successive application of organic material was estimated. According to the estimation, it will take about 20 y to leach a stationary state.
