Microbial biomass and nutrients in soil at the different ages of Citrus in Three Gorges Reservoir area

Microbial biomass, organic carbon (OC), total nitrogen (TN), and microbial biomass C (MBC), N (MBN) in soil were determined at the different ages of Citrus in Three Gorges Reservoir area, China. The results showed that pH increased readily with age of citrus tree, that with age OC increased readily, whereas MBC, MBN, MBC/OC and MBN/TN increased in soil increased quickly, and tended to be highest contents under 20-year citrus tree, after that they decreased. TN in soil was lowest in 20-year citrus site, and was highest in 30-year citrus site. The results suggested that although the increase in the age of citrus favor to accumulation OC, the degree of immobilization of carbon and nitrogen and substrate available is highest before 20-year citrus.