Effects of long-term different fertilization on labile organic carbon in red paddy soil

A long-term field experiment was set in Jiangxi Institute of Red Soil (116°20′24″E,28°15′30″N) in Jinxian county of Jiangxi province, China. One of the aims of the experiment was to study the effects of extensive use of various fertilisers over a long period of time on labile organic carbon pool in red paddy soil. The treatments on use of fertilizers were: (1) no added fertiliser (CK), (2) chemical fertilizers only (NPK), (3) organic fertilizers only (OM) and (4) a combination of chemical and organic fertilisers (NPKM). Results showed contents of soil microbial biomass carbon (MBC), potential mineralization carbon (PMC) and dissolved organic carbon (DOC) in red paddy soil decreased as the soil depth increased. Contents of MBC, PMC, DOC at same soil horizon in different fertilizations decreased in an order of NPKMOMNPKCK. Extensive use of organic fertilizers or a combination of organic and inorganic fertilizers increased MBC, PMC and DOC in red paddy soil, resulting in an increased soil carbon pool. The percentage of different forms of labile organic carbon over the total soil carbon in the A horizon was significantly higher than that in P horizon. And at the same soil horizon, it was found that the percentage of PMC to total soil carbon (R2) the percentage of MBC to total soil carbon (R1) the percentage of DOC to total soil carbon (R3). Under different fertilizations, the percentages of the labile organic carbon to total soil carbon was NPKMOMNPKCK. It was also found that soil labile organic carbon were not only sig-nificantly correlated to soil organic carbon but also interrelated themselves.