Decomposition of Rice Straw and Mineralization of Carbon, Nitrogen, Phosphorus and Potassium in Wheat Field Soil in Western Uttar Pradesh

The decomposition of rice straw buried in the soil in a wheat field under rice-wheat cropping system in western Uttar Pradesh was studied by nylon mesh bag technique and mineralization of C, N, P and K was measured. Three phases in the decomposition of the rice straw were noticed. The first phase lasted for 5 weeks in which the rate of decomposition was relatively faster, followed by the second phase of slow rate of decomposition from 6th to 15th week and then again a faster rate of decomposition in the third phase. By the end of 23rd week 79 per cent of the rice straw had decomposed. Douglas and Rickman model using cumulative degree-day as time unit described the seasonal decomposition of the rice straw satisfactorily (RMSE = 2.79). During decomposition of the rice straw C and K content decreased, N and P content increased and C:N ratio decreased with time. There was practically no N mineralization from the rice straw during the first phase but thereafter N mineralization proceeded gradually. Potassium release was however fast initially and then slowed down, whereas P mineralization proceeded gradually. About 4.5% of the total N, 22.5% of the total P and 79% of the total K present in the rice straw were released within five weeks since its burial in the soil. More than half of the nitrogen in the rice straw mineralized during the third phase of the decomposition. Application of starter N (20–30 kg ha⁻¹) to mitigate the N immobilization due to the rice straw incorporation in the soil is suggested.