Abstract: Soil microbial biomass P(SMBp) is an important resource of plant P nutrition. It changes widely and is influenced by soil conditions. Following additions of different quantities of KH232PO4 (0，10，20，40，80，240 mg P kg-1 soil) together with glucose (5000 mg C kg-1)and urea (200 mg N kg-1 soil), the soils were incubated at 25℃ for 30d. Soil microbial biomass C and P were determined at 2，6，12，18，30d. The purpose was to investigate the influence of inorganic P on soil microbial biomass P and C/P. The results showed that the added phosphates had no significant impact on soil microbial biomass C (SMBc). However, the added P was soon absorbed and accumulated by soil microbial biomass. At the second day, more than half of soil microbial biomass P was contributed by the added inorganic P. When soil Olsen-P was lower than 50 mg kg-1, soil microbial biomass P increased by about 0.65 mg kg-1 soil with increasing 1 mg kg-1 Olsen-P. In contrary, the ratio of soil microbial biomass C to P decreased with increasing soil Olsen-P.

Key words: Inorganic phosphate, Soil microbial biomass P, 32p