Effects of long-term fertilization on particulate organic carbon and mineral organic carbon of the 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 investigate the effects of extensive use of various fertilizers over two decades on particulate organic carbon and mineral organic carbon of the 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 that the content of the free particulate organic matter(fPOM) and occluded particulate organic matter(oPOM) in A horizon was higher than that in P horizon and that the deeper in soil horizon the lower the content of the fPOM and oPOM was.However,the content of mineral organic matter(mOM) exhibited a reverse trend.Extensive use of organic fertilizers, or a combination of organic and inorganic fertilizers helped increase the contents of fPOM and oPOM,content of organic carbon within fPOM and oPOM,and overall carbon level of soil organic matter(SOC) in red paddy soil.The level of the POM in soil aggregates,the content of organic carbon in POM decreased significantly over the size groups: 0.05～0.25mm,0.25～1mm,1～3mm,3mm.It was also found that contents of organic carbon of POM in size groups were higher than that in bulk soil.These results showed that micro-aggregates(0.25mm) enriched and maintain particulate organic matter of the red paddy soil.