Characteristics of Active Organic Carbon in Black Soil under Long-term Fertilization

The characteristics of soil organic carbon and active organic carbon under 30-yr long-term fertilization were investigated in a black soil located in Jilin Province,northeastern China.Results showed that the contents of different active organic carbon were in decreasing order of labile organic carbon(LOC) light fraction organic carbon(LFOC) microbial biomass carbon(MBC) water soluble organic carbon(WSOC).Application of chemical fertilizer alone had little influence on soil organic carbon(SOC) and active organic carbon,while applications of manure and manure plus chemical fertilizers significantly increased SOC and active organic carbon.With manure and manure plus chemical fertilizers application,LFOC and WSOC contents were significantly increased by 122%-258% and 237%-351%,whereas LOC and MBC increased by 72%-98% and 83%-112%,respectively,compared with that chemical fertilizers alone.The sensitive responses of different active organic carbons to long-term fertilizations were observed in the following order: LFOCWSOCMBC≈LOC.LFOC was the best indicator among the available carbon fractions to indicate the SOC change in black soil under long-term fertilization.