Straw return enhances soil phosphorus availability and resupply potential: A global meta-analysis

Straw return is widely used to recycle crop residues and improve soil phosphorus (P) availability. However, its effects on microbial biomass P (MBP), phosphatase activity, and P fractions have rarely been integrated across studies, limiting the interpretation of available P (AP) responses in relation to P resupply and fertilizer management. Here, we compiled 177 studies with 4438 paired observations and used meta-analysis and machine-learning approaches to quantify soil P responses to straw return and identify their main predictors. Straw return only modestly increased soil total P (TP) by 5.5%, but significantly increased AP and MBP by 18.1% and 47.4%, respectively. Acid and alkaline phosphatase activities increased by 21.2% and 15.7%, respectively. Within the Hedley-type fractionation dataset, responses decreased in the order labile P > moderately labile P > non-labile P. AP responded more strongly under moderate hydrothermal conditions. AP and alkaline phosphatase showed the greatest increases at AN < 50 mg kg^-1. Moreover, AP, alkaline phosphatase, and labile and moderately labile P showed pronounced responses in the 20-40 cm soil layer, indicating that straw-induced P changes extend beyond surface soils. Overall, assessing AP together with MBP, phosphatase activity, and P fractions provides a basis for improving site-specific phosphorus management under residue return systems.