Differential Responses of Soil Organic Carbon Fractions and Carbon Turnover Related Enzyme Activities to Wheat Straw Incorporation in Subtropical China

Soil organic carbon (SOC) fractions and C turnover related enzyme activities are essential for nutrient cycling. This is because they are regarded as important indicators of soil fertility and quality. We measured the effects of wheat straw incorporation on SOC fractions and C turnover related enzyme activities in a paddy field in subtropical China. Soil samples were collected from 0–10 cm and 10–20?cm depths after rice harvesting. The total SOC concentrations were higher in the high rate of wheat straw incorporation treatment (NPKS2) than in the not fertilized control (CK) (P?<?0.05). The concentrations of labile C fractions i.e., water soluble organic C (WSOC), hot-water soluble organic C (HWSOC), microbial biomass C (MBC), and easily oxidizable C (EOC)], were higher in the moderate NPKS1 and NPKS2 treatments than in CK and the fertilized treatment without straw (NPK) (P?<?0.05). The geometric means of labile C (GMC) and C pool management index (CPMI) values were highest in NPKS2 (P?<?0.05). The SOC concentrations correlated positively with the labile C fractions (P?<?0.05). Soil cellulase activity and the geometric mean of enzyme activities (GMea) were higher in NPKS2 than in CK in all soil layers (P?<?0.05), and the invertase activity was higher in NPKS2 than in CK in the 0–10?cm layer (P?<?0.05). Stepwise multiple linear regression indicated that the formation of the SOC, WSOC, HWSOC, MBC, and EOC was mostly enhanced by the cellulase and invertase activities (P?<?0.05). Therefore, the high rate of wheat straw incorporation may be recommended to increase soil C pool levels and soil fertility in subtropical paddy soils.