Response Characteristics Of Typical Crop Soil Organic Carbon Fractions To Carbon Input Under Long-term Fertilization In China

Soil organic carbon is an essential indicator to measure the soil fertility. Soil organic carbon represents a high heterogeneity. Because of different chemistry and existing forms, soil organic carbon fractions show different decomposibility and fertility functions. Therefore, investigating soil organic carbon fractions is important for better understanding the stabilization and fertility mechanims of soil organic carbon. Black soil, fluvo-aquic soil, red soil and yellow paddy soil of China were as the research objects, through field sampling, laboratory analysis and soil physico-chemical fractionation procedure, this study was conducted to investigate the relationship between soil organic carbon fractions and carbon inputs under the long-term different fertilization modes. The main results showed as follows:(1) Application of fertilizer plus manure significantly improved the storages of soil total organic carbon and fractions carbon. Compared with no fertilizer treatments(CK), soil total organic carbon storage was significantly increased by 12—85%、15—27% 、13—124% and 7—33% in black soil, fluvo-aquic soil, red soil and yellow paddy soil under the manuring treatments. For black soil, fluvo-aquic soil and red soil, soil organic carbon storages with different carbon pool were significantly increased, but in unprotected carbon pool and physically-protected carbon pool were the most obvious; For yellow paddy soil, soil organic carbon storages only were increased in unprotected carbon pool and physically-protected carbon pool, and had no significant changes in chemically-protected carbon pool and biochemically-protected carbon pool. These studies were shown that application of fertilizer plus manure is effective fertilization mode, soil organic carbon is very sensitive to agricultural measures and is a good indicator in unprotected carbon pool and physically-protected carbon pool. Chemically-protected carbon pool and biochemically- protected carbon pool is the stable carbon pool, it is very important to measure soil organic carbon storages.(2) The relationship between soil organic carbon and cumulative carbon input in different soil types, soil total organic carbon and fractions carbon showed a significant linear increase with cumulative carbon input in black soil, fluvo-aquic soil, red soil, which illustrated that organic carbon of these soil types is not affected by carbon saturation limit and has a large potential of carbon sequestration, and has not yet reach carbon saturation under the current conditions. But soil total organic carbon and fractions carbon showed a significant "saturation curve" increase and no significant linear increase with cumulative carbon input in yellow paddy soil, this means that it has been reached carbon saturation under the current conditions.(3) The efficiency of soil organic carbon sequestration was in the order: black soil(23%) > red soil(10%) > fluvo-aquic soil(5%), respectively under the long-term fertilization. Black soil showed the highest efficiency of soil organic carbon sequestration in chemically-protected carbon pool and biochemically-protected carbon pool, which was 6—9%, and red soil showed the highest in unprotected carbon pool, which was 5—8%. These results demonstrated that organic carbon of black soil directly stored in relatively stable carbon pool, but organic carbon of red soil preferentially storage in activate carbon pool, and then transfer to a most stable carbon pool.