Fe/Al (hydr)oxides engineered biochar for reducing phosphorus leaching from a fertile calcareous soil

Excessive input of phosphate fertilizer into agricultural soils has caused critical environmental concerns due to high phosphorus (P) accumulation in farmland and P leaching into subsurface drainage. In this study, an Fe/Al (hydr)oxides modified biochar (FA-BC) was fabricated from corn straw via a wet-precipitation method and utilized to reduce P leaching from a fertile calcareous soil. Spectroscopic techniques demonstrated that the FA-BC exhibited a higher oxidation resistance than the raw BC due to oxide impregnation on the BC surface. The maximum Langmuir P adsorption capacities (393 and 528 mg kg⁻¹) of the BC (4%, w/w) and FA-BC (4%, w/w) treated soils demonstrated a more efficient P adsorption capacity of the FA-BC. Application of the 2% (w/w) FA-BC also significantly reduced the leaching of total P (81.3%) from the soil column, while maintained an appropriate level of bioavailable P in the soil for sustaining plant growth. The chemical sequestration test and in-situ P k-edge XANES analyses of the FA-BC incubated soils revealed that the labile Ca–P fractions were transformed into stabilized Fe/Al–P complexes. The increased soil pH, a higher degree of soil P saturation, and intensive interaction between P and Fe/Al (hydr)oxides also contributed to the superior ability of the FA-BC amended soils towards P retention. This study provided field-relevant implications for the design and application of engineered biochar for green and sustainable improvement of agricultural soils.