Effects of adding biochar of different particle sizes on hydro-erosional processes in small scale laboratory rainfall experiments on cultivated loessial soil

Abstract

Adding biochar to soil is an efficient method to improve soil physicochemical properties. Understanding the effect of this method on soil and water loss is also important. However, there is insufficient data available to assess this effect. Thus, a simulated rainfall (intensity 90 mm h−1) study was conducted to explore the effect of biochar particle sizes (2–1, 1–0.25, and <0.25 mm) and incubation times (0 and 8 months) of biochar and soil mixture on soil and water loss. Our experiments consisted of measuring soil loss, surface runoff, >2 mm water-stable soil aggregate content, and soil saturated hydraulic conductivity (Ksat) from a perforated box (1 m long and 0.4 m wide) with a 27% slope gradient that contained soil, with a constant application rate of biochar at 1% (wt/wt). Soil without biochar was used as the control. The results indicated that biochar-treated soil delayed the time to runoff compared to the control by 12.67% to 32.58%, with the smallest particle size (<0.25 mm) and 8 months incubation being the most effective. In general, all tested biochar particle sizes had some control on soil and water loss. The total runoff volume after biochar additions of 2–1, 1–0.25, and <0.25 mm particle sizes decreased by 2.04%, 24.21%, and 29.63% and by 14.72%, 13.83%, and 30.76% with no incubation and 8 months of incubation, respectively, while the total erosion decreased by 12.86%, 34.30%, and 34.29% and by 20.41%, 11.85%, and 31.93% with no incubation and 8 months of incubation, respectively, compared to the control. Eight months of incubation could effectively decrease both the total runoff and amount of erosion only for soil amended with 2–1 mm biochar particles compared to those with no incubation. Furthermore, 2–1, 1–0.25, and <0.25 mm biochar treatments could increase >2 mm water-stable soil aggregate content and Ksat relative to the control. We speculated that the positive effects of biochar on soil and water loss were possibly due to an improvement in soil physical properties, such as an increase in the >2 mm water-stable soil aggregate and Ksat.