Amelioration effects of coastal saline-alkali soil by ball-milled red phosphorus-loaded biochar

There is a great demand for amelioration of coastal saline-alkali soil, which requires efficient and economical amendments. Biochar has been proven to be a promising soil amendment and newly modified biochar is competitive for amelioration of coastal saline-alkali soil. Herein, a novel biochar (BPBC) was successfully prepared by ball milling and red phosphorus (P) loading. Ball milling could effectively grind pristine biochar into submicron particles, load uniform and nanoscale P-containing particles on biochar, and hence markedly improve the special surface area, P loading amount, and P-containing functional groups contents. Meanwhile, the oxidative conversion of red P into phosphorus oxides and phosphate was promoted, which could be ascribed to reactions with the minerals and O-containing functional groups of biochar. These reactions also occurred in the amended soil, thus significantly decreasing the soil electrical conductivity and salinity by phosphate precipitation between BPBC and soluble salt ions, and decreasing the soil pH and alkalinity by acid-base neutralization. BPBC improved the soil quality and fertility by enhancing organic carbon content, cation exchange capacity, soil nutrients (e.g., N, P, K), and soil enzyme activities. Moreover, amendment of biochar, especially BPBC, could improve the microbial community structure and promote the germination and growth of maize. Overall, BPBC is a novel, efficient, and eco-friendly soil amendment that is able to ameliorate soil salinity and alkalinity, improve soil quality, and promote plant productivity in coastal saline-alkali soil.