Abstract: In an incubation test, a calcareous soil with low concentration of ava ilable P was amended with KH2PO4 (0, 25, 50, and 100 mg P·kg-1) and g round wheat straw (5 g C·kg-1), and incubated at 25 ℃ for 90 days. The aim was to investigate the change patterns of soil microbial biomass P and microbial P concentration as well as their relationships with soil available P. The results showed that both soil microbial biomass P and microbial P concentration increased with increasing inorganic P addition, with the maximum being 7137 and 10534 mg·kg-1, respectively. The combine d application of inorganic P (except 100 mg P·kg-1) and wheat straw decre ased the soil microbial biomass P and microbial P concentration, being most obvi ous at early incubation period. Soil microbial biomass P and microbial P concent ration had significant positive correlations (P<005) with soil available P (R2=026 and 040, n=49, respectively). The applied P could rapidly transform into microbial biomass P. The maximum apparent contribution rate of applied P to microbial biomass P was 71%. The added wheat straw could further improve the appar ent contribution rate.

Key words: population density, natural environment, man-land relationship, China.