Methane Emission Related to Enzyme Activities and Organic Carbon Fractions in Paddy Soil of South China Under Different Irrigation and Nitrogen Management

Abstract

The objectives of this study were to obtain rational irrigation and nitrogen (N) management for reducing methane (CH4) emission from paddy field and understand how CH4 emission flux is affected by the changes in soil enzyme activities and organic carbon fractions under different irrigation and N management. Two-season field experiments were conducted with three irrigation modes, conventional irrigation (C), “thin-shallow-wet-dry” irrigation (T), and alternate drying and wetting irrigation (D), and two N treatments, 100% urea (FM1) and 50% urea and 50% pig manure (FM2), to investigate CH4 emission flux, soil enzyme activities, and organic carbon fractions and analyze the relationships between them. CH4 emission fluxes from early and late rice fields peaked at tillering stage (652.74 and 103.78 mg m−2 h−1). Compared to C mode, D and T modes increased early rice yield and D mode also increased total yield of both seasons. However, D and T modes decreased cumulative CH4 emissions over the whole growth period under FM2. CH4 emission flux was positively correlated with saccharase activity and microbial biomass carbon (MBC), but negatively correlated with cellulase activity. Path analysis indicates that cellulase activity had a direct negative effect on CH4 emission. FM2-D and FM2-T were rational irrigation and fertilizer treatments for rice production with higher yield and lower CH4 emission, and CH4 emission flux was affected by the changes in MBC, saccharase, and cellulase activities in soils under different irrigation and N management.