Organic carbon content and its liable components in paddy soil under water-saving irrigation

Variation of soil organic carbon (SOC) and its liable fractions under non-flooding irrigation (NFI) were investigated. In NFI paddies, the soil microbial biomass carbon (SMBC) and water extractable organic carbon (SWEC) content in 0-40 cm soil increased by 1.73-21.74% and 1.44-30.63%, and SOC in NFI fields decreased by 0.90-18.14% than in flooding irrigation (FI) fields. As a result, the proportion of SMBC or SWEC to SOC increased remarkably. It is attributed to the different water and aeration conditions between FI and NFI irrigation. The non-flooding water-saving irrigation increased soil microbial activity and mineralization of SOC, which broke down more soil organic nutrients into soluble proportion and is beneficial for soil fertility, but might lead to more CO2 emission and degradation in carbon sequestration than FI paddies.