Biochar affects the distribution of phosphorus in the soil profile by changing the capacity of soil to adsorb phosphorus and its distribution within soil macroaggregates

A large number of studies suggested that biochar can affect the adsorption of phosphorus (P) in soil and the distribution of P in soil aggregates, but it is still unclear whether biochar can indirectly affect the distribution of P in soil profiles through the influence of these two factors. Therefore, the ability of maize straw biochar to mitigate the risk of loss of P and improve the distribution of P in soil profile was evaluated by studying the capacity of soil to adsorb P from the soil and distribution fractions of it in diverse grain-sized aggregates of soil. A 5-year field trial site had received NPK fertilizer inputs at the same rate and one-time biochar inputs at different rates (0, 15.75, 31.5 and 47.25 t ha(-1)) at the beginning of the experiment. Langmuir and Freundlich equations were fitted to the sorption data of the soil and suggested that the applicataion of biochar can promote P absorption capacity of soil, particularly when the rates of biochar applied were 31.5 and 47.25 t ha(-1). Biochar can improve the stability of soil aggregates, and aggregates with particle sizes of 0.25-2 mm have the highest relative rate of contribution to various fractions of P in the soil. Biochar can promote the accumulation of most of the P fractions in soil aggregates, particularly when the rates of biochar applied were 31.5 and 47.25 t ha(-1). The TP, Ca-2-P, Al-P, Ca-8-P, moderately labile organic phosphorus (MLOP) and moderately resistant organic phosphorus (MROP) were primarily distributed in the 0-20 cm soil layer. Biochar increased the contents of MLOP and highly resistant organic phosphorus in the soil layer of 0-20 cm while reducing the contents of Al-P, Fe-P and occluded phosphorus (O-P) in the soil layer of 0-20 cm and decreased the contents of TP, Ca-8-P, O-P and MROP under the 20 cm soil layers. Biochar can change the distribution of P fractions along the soil profile by improving the adsorption of soil P and its distribution in the soil aggregates (0-20 cm).