Coupling amendment of biochar and organic fertilizers increases maize yield and phosphorus uptake by regulating soil phosphatase activity and phosphorus-acquiring microbiota

Biochar and organic fertilizers are important alternatives to mineral fertilizers. Thus, it is important to understand how the co-application of biochar and organic fertilizers influences crop productivity and soil-plant phosphorus (P) trade-offs. Herein, we conducted a field fertilization experiment for eight years with maizecabbage rotation. This experiment contained five treatments: no fertilization (CK), mineral fertilizers (CF), CF + biochar (BF), 20% substitution of mineral nitrogen (N) with organic fertilizers (OF), and OF + biochar (BOF). The fertilization regimes of all plots were maintained since 2013. The results showed that soil P pool composition but not P bioavailability differed significantly between the five treatments. Compared with the CF treatment, soil labile-P content in the BF, OF, and BOF treatments significantly increased by 12-23% and soil stable-P content decreased by 13-19%. Besides, the soil moderately labile-P content in the OF and BOF significantly decreased by 40% and 10% and increased by 31% in the BF as compared to the CF. The activities of soil acid (ACP) and alkaline phosphatase (ALP) in the BF, OF, and BOF significantly increased by 8-44% and 16-49% respectively compared to the CK. Furthermore, the abundance of P-acquiring genes (bpp, phoD, phoX, ppx, ppk, and phnK) in the BF, OF, and BOF increased by 22-114% compared to the CK. Plant P uptake and maize yield were significantly correlated with soil ACP and ALP activities as well as the abundance of phnK, ppx, phoD, phoX, and pqqC genes but not to the contents of soil P components. In conclusion, the co-application of biochar and organic fertilizer on maize productivity increases was mainly related to the improvement of soil phosphatase activity and P-acquiring gene abundance.