Practices sustaining soil organic matter and rice yield in a tropical monsoon region

Sandy soils are usually dominant in tropical monsoon regions, due to the high weathering potential associated with high temperatures and precipitation. The organic matter content of sandy soils is low due to low clay content and high microbial activity. Therefore, soil management practices that alter the soil organic carbon (SOC) content may be important for the sustainable management of crop yields. Thus, the present study investigates the distribution of rice yield and SOC content under different land management practices and analyzes the relationship between rice yield and SOC with pertinent management practices (manure and fertilizer applications). The soil horizons from 0-to 40-cm depths were collected in each layer to measure SOC and soil properties at 64 sites. At each sampling site, farmers were given questionnaires and the record book for the standards for good agricultural practices of farm owners were gathered to assimilate information on rice yield and their practices during 2010-2014. The mean rice yield of the whole crop year and SOC were 2.93 Mg ha(-1) and 47.09 Mg C ha(-1), respectively, in the irrigated areas, and were 2.38 Mg ha(-1) and 32.08 Mg C ha(-1) in the rain-fed areas. Significantly higher values were obtained in the irrigated areas (p < 0.05). There was a significant positive correlation between rice yield and SOC in both the irrigated areas (R-2 = 0.72, p < 0.01) and the rain-fed areas (R-2 = 0.85, p < 0.01); however, the slopes of these regression equations were significantly different. In both irrigated and rain-fed areas, manure should be applied every year, with an optimal application rate of N, P, and K fertilizers being selected. The combination of manure, fertilizer, and increasing irrigation facilities the maintenance of SOC levels and substantially increases rice yields.