Effects of land use type on soil organic carbon and its fractions

To address how land use change affects soil organic carbon and its fractions, we sampled soil and measured contents of soil organic carbon, microbial biomass carbon, readily oxidizable carbon and light fraction carbon in five different land use types, i.e. artificial grassland(AG), grazing exclusion(GE), cropland(CP), fallow(FL) and free grazing grassland(FG). The content of soil organic carbon was(14.98 ± 3.47) g·kg-1 in AG,(12.41 ± 6.40) g·kg-1 in GE,(12.20 ± 5.59) g·kg-1 in CP,(10.39 ± 5.08) g·kg-1 in FL and(9.45 ± 3.19) g·kg-1 in FG. Soil organic carbon content in AG was significantly higher than that in other types of land use, and that in FG was the smallest among the five land use types. Soil organic carbon content was similar between GE and CP. The pattern of microbial biomass carbon, readily oxidizable carbon and light fraction carbon among the five land use types were similar to that of soil organic carbon. The contents of soil organic carbon and its fractions decreased gradually with increasing soil depth. In the five land use types, the ratio of microbial biomass carbon, readily oxidizable carbon and light fraction organic carbon to total soil organic carbon were 0.24%-0.66%, 0.002%-0.019% and 0.05%-0.25%, respectively. These results suggest that different fractions of soil organic carbon differ in the sensitivity to environmental change. Our results confirms that the index of soil microbial carbon can be regarded as the sensitive index indicating the change of soil organic carbon and soil fertility, which can reflect the change of soil organic carbon in the early stage