Biochar application reduces soil detachment capacity by overland flow under a continuous three-year field experiment on the Loess Plateau of China

Abstract

Variation of soil properties induced by biochar amendments affects soil detachment capacity (D_c). However, the long-term effects of biochar on D_c have remained unexplored. This study assessed the variation of D_c with the rates and elapsed time since apple branch-derived biochar application, and quantified the relationship of D_c with hydrodynamic parameters and soil physicochemical properties in a three-year field experiment. Undisturbed soil samples to 20 cm depth were collected by using steel rings from field plots treated with biochar at 0, 24, 60, 96, 132, and 168 t ha⁻¹ after biochar application for 1, 2 and 3 years. The D_c of these samples was evaluated through a flume experiment, with scouring soil samples under three flow discharge rates (0.00025, 0.00045, and 0.00065 m³ s⁻¹) and five slope gradients (5.24, 8.75, 17.63, 26.79, and 40.40 %). Results revealed that, compared with no biochar treatment, the application of 24∼96 t ha⁻¹ biochar after 1–2 years generally resulted in a reduction of D_c ranging from 6 %∼80 %, with a mean of 36 %. Conversely, 132 and 168 t ha⁻¹ biochar application increased D_c by 59 % and 45 %. All biochar treatments after 3 years resulted in a 48 % reduction in D_c relative to bare soil. The D_c generally decreased with an increasing of rates and elapsed time since biochar application. The mean weight diameter of soil aggregates (MWD) and cohesion (COH) were the key indices influencing D_c in the first two years, while total organic carbon (TOC) started to significantly affect D_c in the last year. Shear stress (τ) emerged as the optimal hydrodynamic parameter for simulating D_c. Power function equations well estimated D_c using τ, MWD, COH, and TOC under biochar application. These results demonstrate that applying biochar with sufficient elapsed time since application and low rates, rather than minimal elapsed time since application and high rates leads to a greater enhancement of soil erosion resistance for loess soils, with potential to control rill erosion for degraded or degrading sloping farmland at risk of erosion on the Loess Plateau.