Effects of the different long-term fertilizations on fractions of organic carbon in Fluvo-aquic soil

The density fractionation scheme was used to study the changes of organic carbon fractions and their distribution in Fluvo-aquic soil under different long-term fertilizations. The results showed that compared to no fertilization (CK), contents of coarse free particulate organic carbon (cfPOC), physical protected intra-microaggregate particulate organic carbon (iPOC) and mineral-associated soil organic carbon(mSOC) were all increased significantly under the balanced chemical fertilization(NPK), straws plus with chemical fertilization (NPKS), and manure added with chemical fertilization (NPKM and 1.5NPKM). The cfPOC fraction with the highest magnitude of increased by 114.5%–278.9％ indicates it was more sensitive to the fertilizations than other organic carbon fractions. The mSOC, accounting for 67.0% to 80.4% of total organic carbon (TOC), was main form for organic carbon sequestration in Fluvo-aquic soil. Application of unbalanced chemical fertilization (N and NP) was apt to increase free POC content, and for other fertilizations, about 49.1%–58.1% of TOC was transferred to mSOC, 26.2%–31.7% to free POC and 15.7%–20.9% to iPOC. It could be concluded that long-term manure application with chemical fertilizers or straw incorporation to soil was more benefit to organic carbon pools upgrade in Fluvo-aquic soil.