Abstract: Seven soils with different land use types were collected from semi-arid area and treated by dry-sieving. Distribution of microbial biomass P (MBP), available P (AP), organic P (OP), labile organic P (LOP), moderately labile organic P (MLOP), moderately resistant organic P (MROP) and highly resistant organic P (HROP) were studied. The results showed that the content of MBP and OP in whole soil and aggregates were 5.86-12.24 mg·kg-1, 0.12-0.35 g·kg-1, the irrigated arable soil and the grassland soil had the highest and lowest value, respectively. The amounts of MBP and OP in large aggregates (＞2 mm) were higher than in small aggregates (＜2 mm), and the AP in small aggregates was higher than in large aggregates. The result also showed that large aggregates had higher content of MROP and HROP, large and small aggregates were both rich in LOP and MLOP. These results suggest that the large aggregates may be the pool of soil P transformation, and the small aggregates are the source of soil available P. There were significant correlation between MBP and different types of soil phosphorous.

Key words: Soil aggregates, Microbial biomass P, Soil organic P, Semi-arid area