Field study on the hydraulic behavior of heavy soil: Effects of biochar application rates

The amount of biochar applied in soil amendment significantly influences environmental impact, cost-efficiency, and soil improvement effectiveness. However, there is limited understanding of how varying biochar application rates affect the hydraulic performance of fine-textured soils under field conditions. A field-scale evaluation was conducted to determine how various rates of poplar wood waste biochar (0, 25, 50, and 75 t ha^-1) influence the hydraulic characteristics of clay loam soil. Key soil physical and hydraulic properties were assessed, including mean weight diameter (MWD), bulk density (BD), average infiltration rate, soil moisture, flow dynamics in different pore classes, and both saturated and near-saturated hydraulic conductivity. The results showed that biochar application at 50 and 75 t ha^-1 significantly increased MWD by 13.0 % and 17.7 %, field capacity by 3.7 % and 7.5 %, and permanent wilting point by 3.0 % and 6.1 %, respectively, while reducing BD by 14.5 % and 17.8 % compared to the control. A clear positive trend was observed between biochar application rate and average infiltration rate, with the highest rates (50 and 75 t ha^-1) yielding the most substantial improvements in water infiltration. Applying biochar at 50 t ha^-1 significantly improved saturated and near-saturated hydraulic conductivity in fine-textured soils by enhancing macropore flow, indicating beneficial changes to soil pore structure. This rate provided the best balance between improving soil hydraulic properties and resource efficiency, highlighting its potential as a sustainable practice to boost water infiltration and retention in water-limited agricultural systems.