Utilization of rice straw for paddy soil fertility improvement

Results from the laboratory part showed that with submerged paddy, calcareous Lop Buri soil series, rice straw reduced soil pH and NH4-N content but increased EC, soil reduction and available K content. The combination of rice straw and chemical fertilizer lower soil pH than that with chemical fertilizer alone and gave higher EC, soil reduction and available K content. For submerged paddy, acid sulfate Rangsit soil series, rice straw increased soil pH, EC, soil reduction and available soil P and K contents but decreased soil NH4-N content. The combination of rice straw and chemical fertilizer gave higher soil pH, EC, soil reduction and available K and P contents than with chemical fertilizer alone. From the greenhouse experiments with Lop Buri soil series, application of chemical fertilizer in combination with rice straw or rice straw compost resulted in better growth rate, N, P and K absorption and higher rice yield than that with only chemica fertilizer. The increase in percentage of rice yield from those receiving chemical fertilizer supplemented with rice straw at 3, 6 and 9 g/kg soil with respect to chemical fertilizer were 132, 117 and 88 percent respectively whereas those of supplemented with rice straw compost at 3, 6 and 9 g/kg soil with respects to chemical fertilizer were 66, 106 and 148 percent respectively. For Rangsit soil series, the application of chemical fertilizer in combination with rice straw resulted in lower growth and lower rice yield than that with only chemical fertilizer. However, the combination of chemical fertilizer with rice straw compost gave better growth rate and higher rice yield than that with only chemical fertilizer in which at the application rate of rice straw compost of 9 g/kg soil gave the highest increase in percentage of rice yield of 13 percent with respect to chemical fertilizer. Furthermore, it was observed that application rate of rice straw compost of 9 g/kg soil gave the highest increase in percentage of rice yield of 13 percent with respect to chemical fertilizer. Furthermore, it was observed that application of rice straw with chemical fertilizer under prolong submerged condition increased the efficiency of rice straw in increasing rice yield, especially, at the lower application rat of 3 g/kg soil. At this rate, it gave the highest increase in percentage of rice yield of 7 percent with respect to chemical fertilizer. Therefore, rice straw could be used directly in combination with chemical fertilizer without prior treatment as a compost. Furthermore, it was required at a lower rate than the compost to give similar results. In addition, with calcareous Lop Buri soil series, application of rice straw in combination with chemical fertilizer gave significant higher growth, yield and total N P and K uptake of Khao Jao, Haum Suphanburi rice and Suphanburi 1 rice than that with only chemical fertilizer. The appropriate application rate of rice straw as a supplement of chemical fertilizer was at 3 g/kg soil and the appropriate method of application of rice straw in combination with chemical fertilizer was application of rice straw together with chemical fertilizer and pre submergence for 1 week before transplanting.