Intercropping controls the response of phosphorus availability to fertilization

Phosphorus (P) availability is fundamental for ensuring sustainable food production in global croplands. Intercropping is a sustainable way that promotes P availability, addressing the multiple challenges of scarcity of P rock and exacerbating pollution. Yet, how intercropping regulates the transformation of P availability from inorganic and organic P fractions in unfertilized cropland is poorly understood. Here, we conducted a 5-year field experiment to evaluate the effects of intercropping and P fertilization on the P fractions and to explore the mechanisms of these effects. Results showed that P fertilization increased inorganic and organic P fractions, on average, 1.64 and 2.30 times higher than those in unfertilized soil. Intercropping interacted with P fertilization to affect the content of P fractions. More specifically, soil labile inorganic P increased by unfertilized intercropping, while decreased by fertilized intercropping than monoculture. Unfertilized intercropping increased the ratio of labile inorganic P to moderately stable organic P, while decreasing soil moderately stable organic P. Furthermore, soil microbial diversity and biomass, as well as soil properties predicted changes in P fractions, especially microbial biomass carbon was positively correlated with labile inorganic P and the ratio of both P fractions, while negatively correlated with moderately stable organic P. Our findings suggest that intercropping increases P availability in unfertilized soil by transforming moderately stable organic P to labile inorganic P, and accumulation of microbial biomass mainly drive transformation process.