Carbon addition reduces labile soil phosphorus by increasing microbial biomass phosphorus in intensive agricultural systems

Accumulation of inorganic and labile organic phosphorus (P) in intensive agricultural systems leads to P loss from soil which can cause serious environmental problems. Soil microbes are important in mobilizing soil non‐available P, however, little is known about the role of soil microbes in immobilizing P to reduce P loss. Here, we test whether stimulating microbial biomass to immobilize P could reduce the amount of labile P available for leaching. The distribution characteristics of Olsen P, organic P and microbial biomass P were determined in three intensive agricultural systems. In addition, we conducted a pot experiment with three P and four carbon (C) levels. CaCl 2 extractable P was measured and used to indicate the risk of P leaching. We found that there was a positive relationship between soil organic C and microbial biomass P. Carbon addition drove the process of P immobilization and reduced CaCl 2 extractable P. Microbial biomass P increased by 64% ( p  < .05) with the addition of C, and Olsen P and CaCl 2 extractable P decreased by 28% and 17%, respectively. Our results show that C addition increased microbial immobilization of P and reduced forms of labile P susceptible to leaching. Stimulating microbes to immobilize P by adding C to soils may have the potential to reduce P loss from intensive agricultural systems, reducing their environmental impact.