Biochar Addition Regulates Soil Phosphorus Fraction and Improves Release of Available Phosphorus Under Freezing-Thawing Cycles

Currently, the shortage of phosphorus resources is becoming more and more serious, in general, phosphorus fertilizer is easily fixed by soil causing low the utilization rate and excess accumulation in soil. Freezing-thawing cycles (FT) is a seasonal phenomenon occurring in high latitudes and altitudes regions, which has a great influence on the form of phosphorus in soil. This study investigates the effect of biochar on phosphorus form and availability under freezing-thawing and constant temperature conditions. The research results show that biochar and freezing and thawing cycles can not only directly change the soil phosphorus pool, but also change the soil physicochemical properties (e.g., pH, electrical conductivity, organic matter) and microbial communities, which further affect the adsorption and mineralization of phosphorus in the soil. Moreover, according to Hedley-P classification results, under FT condition, the content of labile phosphorus pool is always greater than those under TH (Thermostatic incubation) condition. Freezing and thawing cycles may promote the conversion of phosphorus from other components to unstable phosphorus pools. The results of this study will be devoted to understand the changes in soil phosphorus composition under the effects of biochar addition and freezing-thawing cycles, providing references for agricultural production in areas where freezing-thawing occurs