Soil phosphorus availability and cotton growth affected by biochar addition under two phosphorus fertilizer levels

The responses of soil P availability and cotton growth to biochar addition under different P supply levels are not well documented. Thus, a pot experiment was conducted to investigate the effects of biochar addition on soil nutrient status, microbial characteristics related to P cycling and cotton growth with or without adequate P supply. Biochar was added to soil grown cotton at three rates of 0, 3 and 30 t ha−1 under two P fertilizer levels of 0 and 150 kg P2O5 ha−1, respectively. Results showed that biochar addition had significantly positive effects on soil P availability, phosphate solubilizing bacteria number, phosphatase activities (except acid phosphatase activity), cotton nutrients uptake and seedcotton yield, regardless of P fertilization level. The magnitude of soil available P content increase after biochar addition with P fertilizer was greater than without P fertilizer. And 3 t ha−1 biochar was better than 30 t ha−1 biochar for converting soil P into available P. Under a given P fertilizer level, biochar addition had fertilizer-like diminishing effect on seedcotton yield. Conclusively, the co-application of P fertilizer and the appropriate amount of biochar could be beneficial for soil P availability in cotton production.