A suitable fractionation method of phosphorus (P) is a key to effective assessment of soil P componential features. Here a new biologically-based P (BBP) method was used to evaluate the P fractions in the upland and paddy soils across large-scale area in China. The soil P was divided into four components:① soluble or rhizosphere-intercepted (CaCl2-P), ② organic acid activated and inorganic weakly bound (Citrate-P), ③ enzyme mineralization of organic P (Enzyme-P), ④ potential activation of inorganic P (HCl-P). Then, the relationships between biologically-based P fractions and standard Olsen-P were investigated, and driving factors of P fractions were identified. The results showed that P content was in order of HCl-P>Citrate-P>Enzyme-P>CaCl2-P. All P components of upland soil displayed higher levels than those of paddy soil. Moreover, the P components were highly positively correlated with the Olsen-P, suggesting that each P component contributed to soil P availability. However, it was found that Olsen-P was most highly correlated with CaCl2-P and Enzyme-P (R2=0.359; R2=0.386) in upland soil, while Olsen-P was most highly with Citrate-P (R2=0.788) in paddy soil. This result indicated that available P of upland soil was mainly from organic P mineralization and soluble P, and available P in paddy soil was mainly from inorganic P activation. Redundancy analysis (RDA) showed that the P components were mainly affected by soil pH and silt content, which suggested that it could enhance the P availability via regulating soil pH in the agricultural activities.
Keywords: bio-availability; environmental factors; paddy soil; phosphorus fractionation; upland soil.