Rice straw amendment and sulfateAffecting methane production and chemical properties in paddy soils

Abstract

Rice straw is an important organic source for paddy soil improvement, but it is also a source for methane (CH 4 ) fermentation in flooded paddy. In contrast, sulfate (SO 4 2-) is a source of electron acceptor in anoxic condition which plays a role in reducing CH 4 production. Therefore, this incubation was conducted with the aim of investigating the effect of rice straw amendment in combination with SO 4 2-on some soil chemical change in 3 different-textured paddy soils. Five rice straw amendment rates, 0, 6.25, 12.50, 18.75 and 25 t/ha; and 2 rates of SO 4 2-, 100 and 200 kg/ha were anaerobically incubated in loam, clay and loamy sand soils, arranged in 5x2 factorials with triplicate. Results showed that rice straw amendment significantly increased (p?0.01) CH 4 production with increasing rate of rice straw positively correlated with labile organic carbon (LOC), pH, and electrical conductivity (EC) in all soil types, except for pH in loamy soil which was negatively correlated. However, 200 kg/ha of SO 4 2-had stronger potential to suppress CH 4 production than 100 kg/ha, which showed in clay and loamy sand. The highest range of CH 4 production was in clay followed by loam and loamy sand at all rates of rice straw, except at 25 t/ha of rice straw in loam and clay which gave the same range. In addition, LOC, pH and EC also significantly increased (p?0.001) with increasing rate of rice straw regardless of SO 4 2-in each of soil types. The highest LOC and EC were found in clay followed by loam and loamy sand, but the same range of pH was observed in both of loam and clay, and lower in loamy sand. Although, rice straw application had potential to increase CH 4 production from paddy soils, it promoted soluble ions in soil.