Influential Factors Of Microbial Biomass C/P In Calcareous Soil

Soil microbial biomass P is a valuable resource to plant P nutrient, and also play an important role in the transformaion of soil phosphorus. Calcareous soil is the main type soil in the North of China. In this study, two calcareous soils with different Olsen-P were treated with different residues of winter wheat, maize, cotton, soybean and different inorganic P addition of 0,25 , 50 and 100 mg P kg^-1 soil as KH₂PO₄ The soils were incubated at 25℃ for 90 days. Soil microbial biomass C and P, soil CO₂ respiration, microbial community were routinely measured during the incubation. The main resultsSoil microbial biomass C/P was significantly influenced by soil available P. Adding high inorganic P resulted in high soil available P and soil microbial bimass C and P. Soil microbial biomass P increased from 6.7 μg g^-1 to 39.9 μg g^-1. However, the ratio of soil microbial biomass C/P significantly and proportionally decreased with the quantity of added inorganic P. The lowest ratio value was 3. Adding crop straw together with inorganic P could increase the ratio. In particular, the ratios were much higher than others at initial 60 days during the 90 days incubation.Highest C/P ratio of 639 were determined at the treatments with adding soybean straw. Adding crop straws lightly influenced soil microbial biomass P and the ration of soil microbial biomass C/P.There was a link between microbial community structure and soil microbial biomass C/P. Higher values of C/P resulted in lower microbial activity.