Effect of Pisha Sandstone and Biochar on Improving the Physical Properties of a Sandy Soil Under Constant Mechanical Stress

ABSTRACT Soils in the Jin‐Shaan‐Meng region are prone to erosion and poor water retention, restricting agricultural productivity. Despite the known benefits of soil amendments like Pisha sandstone and biochar, their combined effects on sandy soil properties remain underexplored, particularly under constant mechanical stress conditions. We conducted a controlled indoor incubation with combinations of five Pisha sandstone ratios (0%, 25%, 50%, 75%, 100%) and three biochar application rates (0%, 2%, 4%) under constant mechanical stress, measuring bulk density, shear strength, hydraulic conductivity, water retention, and X‐ray micro‐computed tomography (X‐ray micro‐CT) derived soil structure. The results indicate that both amendment materials significantly increased soil compressibility, as evidenced by decreased bulk density driven by Pisha sandstone's silt‐clay fractions optimizing soil particle arrangement, and biochar's low particle density plus porous structure buffering particle compression under constant mechanical stress. However, no significant difference in bulk density was observed between the 2% and 4% biochar treatments. Soil erodibility, assessed through shear strength and aggregate size distribution, was generally increased with biochar alone but substantially reduced at 25%–50% Pisha sandstone content combined with 4% biochar, caused by their synergistic interaction: biochar acts as a “cementing agent” and Pisha sandstone provides skeletal support to enhance inter‐particle occlusion. X‐ray micro‐CT analysis revealed improved pore structure with the incorporation of biochar and Pisha sandstone by increasing pore connectivity and micropore abundance. Soil water retention was markedly enhanced at the 4% biochar rate, underscoring the critical role of biochar in improving the physical properties of sandy soil.