Effects of biochar amendment on the surface and underground runoff and soil loss of karst slopes at the microplot scale

Abstract

Biochar may affect soil erosion by affecting soil structure and has received attention, but its role in karst areas with complex runoff and soil loss processes at the surface and underground is poorly understood. The objective of this study was to investigate the runoff and soil loss characteristics at the surface and underground after two years of soil amendment by corn straw biochar on karst slopes. The rainfall experiments were conducted on a simulated karst microplot in the laboratory. Three biochar application rates, i.e., 15, 30 and 60 t ha−1, were used, and no biochar application measure served as the control (hereafter called T1, T2, T3, CK). The runoff and soil loss samples from the surface and underground were collected under four successive rainfall events with 24 h intervals. The rainfall intensity was 50 mm h−1, and the duration of each rainfall event was 90 min. The results showed that biochar significantly increased the surface runoff (SR) rate (P < 0.05) and surface soil loss compared to the CK. The rates of subsurface runoff (SF) and underground leakage runoff (UFR) decreased significantly after biochar application compared with CK (P < 0.05). The mean UFR rate of CK was 1.6–31.5 times higher than that of T1, T2 and T3, suggesting that biochar application increased surface runoff while decreasing underground runoff. SR accounted for the largest proportion of total runoff (18–88 %), followed by SF (3–30 %) and UFR (1–18 %), which depended on biochar application rates and rainfall events. In addition, in the first and second rainfall events, compared to the CK, biochar application significantly increased the SR rate (P < 0.05), and the increment increased with increasing biochar application amount. However, from three to four rainfall events, no significant difference (P > 0.05) in SR was observed among the four treatments; meanwhile, no obvious regularity was found between different rainfall events for T1-T3, suggesting that successive rainfall is an important factor affecting SR, while it slightly affected SF and UFR. Regression analysis showed that the changes in surface soil loss with increasing SR rate could be described by a power function (P < 0.05) for CK, T1 and T2. Our results indicate that biochar may reduce underground runoff on karst slopes, which means that soil amendment by biochar may be beneficial in karst areas with serious underground leakage.