Distribution characteristics of microbial biomass carbon in different soil aggregates in semi-arid area

Seven soil samples under different managements were collected from semi-arid area of Inner Mongolia. Soil aggregates were obtained with dry sieving method. The contents of organic C and microbial biomass C were analyzed. The results showed that the soil with highest content of organic C had the highest proportion of large soil aggregates. The content of microbial biomass C in whole soil was highest in irrigated soil and was lowest in cole-potato rotation soil,and the amounts were 336 and 189 mg·kg-1, respectively. Soil microbial biomass C in aggregates ranged from 153 to 324 mg·kg-1, and it was highest in the 5 mm fraction of irrigated soil but lowest in the 0.25 mm fraction of grassland soil. There was a close correlation between soil organic C and microbial biomass C. The large aggregates (2 mm) contained more higher amounts of both the soil organic C and microbial biomass C than the small aggregates. No significant correlation was found between soil microbial biomass C and K2SO4-extracable C. The small aggregates contained much higher K2SO4-extracable C than the large aggregates. No significant correlation was found between soil microbial biomass C and K2SO4-extracable C.