Fractions and spatial distributions of agricultural riparian soil phosphorus in a small river basin of Taihu area, China

Abstract Soil samples were collected from three different ranks riparian soil profiles in a small river basin of Taihu area in China. The method of modified Hedley phosphorus sequential fraction was employed to characterize soil phosphorus fractions. The results showed that the riparian soil total phosphorus (TP) contents, organic phosphorus (OP) and inorganic phosphorus (IP) of the basin ranged from 234.98 to 542.29, 49.76 to 73.81, 161.17 to 492.54 mg kg−1, respectively. HCl-Pi, NaOH-Pi and residual Pi were the major part of IP, accounting for 28, 28 and 26% of IP respectively, but NaHCO3-Pi was accounted for 18% of IP. Overall, the various forms of phosphorus, except for Residual P, had a decreasing trend with soils depth. The vertical distributions of TP and IP had same rank order (Riparian Hejiabang > Riparian wuxidang > Riparian Yincungang), while the opposite trend was observed for OP. Surface soils in Riparian Yincungang had lower SOM (soil organic matters):OP ratios than Riparian Wuxidang and Riparian Hejiabang, reflecting the higher probability of OP mineralization in uncultivated soils. Besides, there was significant correlation between phosphorus fractions and SOM, bulk density and capillary porosity.