Soil organic carbon active fractions as early indicators for total carbon change under straw incorporation

Changes in total organic C (C (T)), water-soluble organic C (C (WS)), microbial biomass C (C (MB)), C mineralization, particulate organic C (C (P)), labile organic C (C (L)), C management index (CMI), and C storage in surface Hapli-Ustic Cambisol (0-20 cm) under straw incorporation after both 2- and 10-year durations were investigated in a maize (Zea mays L.) field experiment in northeast China, in order to examine the effectiveness of these active C fractions and CMI as early indicators for total C change. The treatments included straw removal (0%S), 50% of straw incorporation (50%S), and 100% of straw incorporation (100%S). Under the straw incorporation, C (T) concentration and C storage did not significantly change under 2-year duration, while were significantly increased under 10-year duration. However, C (MB), total C mineralization (C (TM)), C (P), and C (L), and CMI were significantly increased under the straw incorporation even after only 2-year duration, and the responses were more significant after 10-year duration. There were positive correlations between all these C indicators with each other. Our findings demonstrate that the measured active C fractions (except for C (WS)) and CMI can provide an early indication of change in total soil organic C induced by straw incorporation.