Effect of corn stalk biochar on hysteresis of soil water characteristic curves of reconstituted soils

Biochar amendment alters soil pore structure and hydraulic properties. This study examines how biochar influences the soil water characteristic curve (SWCC) and its hysteresis by analyzing the effects of biochar content, particle size, and soil shrinkage in two reconstituted soils under drying–wetting cycles using the tensiometer method. It was found that biochar amendment significantly shifts the SWCC upward by enhancing soil porosity and optimizing the pore structure, particularly the proportion of mesopores (5–30 µm), this enhancement in water retention capacity becomes more pronounced with higher biochar content and smaller particle size. Biochar mitigates soil shrinkage due to its lower shrinkage capacity compared to that of the soil matrix. The mean degree of hysteresis was positively correlated with biochar content ( R 2 = 0.86) and negatively with particle size ( R 2 = 0.96), attributed to biochar‐induced pore irregularity, which intensifies the “ink‐bottle effect.” The promoting effect of biochar on soil micropore heterogeneity and its inhibitory effect on volumetric shrinkage exert opposing influences on the hysteresis effect. This study provides mechanistic insight into SWCC hysteresis from an “amendment‐matrix” perspective, forming a basis for optimizing biochar use in agriculture.