The use of biologically based phosphorus fractions to evaluate soil P availability in reduced P‐input paddy soils

Abstract

Abstract Chemical soil phosphorus (P) extraction has been widely used to characterize and understand changes in soil P fractions; however, it does not adequately capture rhizosphere processes. In this study, we used the biologically based phosphorus ( BBP ) grading method to evaluate the availability and influencing factors of soil P under four P fertilizer regimes in a typical rice–wheat cropping rotation paddy field. Soil P was assessed after seven rice‐growth seasons at multiple growth stages: the seedling, the booting and the harvest stage. Soil CaCl 2 ‐P, citrate‐P and HC l‐P (inorganic P, Pi) as well as enzyme‐P (organic P, Po) were not significantly different between soil treated with P fertilizer during the wheat season only ( PW ) and during the rice season only ( PR ) compared with soil treated during both the rice and the wheat seasons ( PR +W) at all three rice‐growth stages. No P fertilizer application during either season (Pzero) significantly reduced the concentration of soil citrate‐P and HC l‐P at the rice‐seedling and harvest stages. Significant correlations were observed between the HC l extraction and Olsen‐P ( R 2 = 0.823, P < 0.001), followed by enzyme‐P ( R 2 = 0.712, P < 0.001), citrate‐P ( R 2 = 0.591, P < 0.001) and CaCl 2 ‐P ( R 2 = 0.133, P < 0.05). Further redundancy analysis ( RDA ) suggested that soil alkaline phosphatase (S‐ ALP ) activity played a role in soil P speciation changes and was significantly correlated with enzyme‐P, citrate‐P and HC l‐P. These results may improve our ability to characterize and understand changes in soil P status while minimizing the overapplication of P fertilizer.