In this study, the effect of biochar application on soil erosion and nutrient loss on karst slopes was investigated under dual surface-underground flow path conditions. Four application rates of biochar to soil considered (0 t ha⁻¹ (CK), 15 t ha⁻¹ (B15), 30 t ha⁻¹ (B30), and 60 t ha⁻¹ (B60)). The experiment was conducted by simulating rainfall, the rainfall intensity was set to 50 mm h⁻¹, and the slope was 25°. Measurement indications are the following: surface runoff (SR), subsurface runoff (SBR), underground fissure runoff (UFR), and concentrations and output loads of total carbon (TC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK) in runoff. The results showed that compared to those under CK, biochar increased SR by 98.92–172.40% and decreased SBR and UFR by 72.69–77.00% and 43.07–94.71%, respectively. Biochar reduced the TC concentration in UFR with increasing biochar application rate, while there were no obvious patterns of the TC concentration in SR and SBR. Compared to those under CK, the TN concentration in SR decreased under the B15, B30, and B60 treatments, while it increased in SBR with almost no difference in UFR. There was no significant difference (P > 0.05) in the TP concentration among the four treatments. The output of TC, TP, and TK through SR dominated accounting for 60–97% of the total load. However, the TN output load in SR was low, and the proportion of its load in the total output load was less than 30%. This study concluded that compared to those in the absence of biochar application, the biochar treatment increased SR by 98.92–172.40%, but reduced the SBR and UFR by 43.07–94.71%. Biochar application increased the total output loads of TC, TP, and TK but decreased the total output load of TN. In summary, biochar alters the pore structure of karst soil, reduces the soil infiltration capacity, and ultimately increases SR and decreases UFR. More importantly, biochar application plays a vital role in regulating water, soil, and nutrient loss at the surface and underground flow paths in karst slopes. Moreover, biochar reduces the TN loss. The results can provide a theoretical basis for the study of the influence mechanism of biochar on soil erosion and the nutrient output in karst mountainous areas.

本研究在地表-地下双重流路条件下研究了生物炭的施用对岩溶斜坡土壤侵蚀和养分流失的影响。考虑了生物炭对土壤的四种施用率（0 t ha ^-1 (CK)、15 t ha ^-1 (B15)、30 t ha ^-1 (B30) 和 60 t ha ^-1 (B60)）。实验采用模拟降雨方式进行，降雨强度设定为50 mm h ^-1，坡度为25°。测量指标有：地表径流（SR）、地下径流（SBR）、地下裂隙径流（UFR）以及总碳（TC）、总氮（TN）、总磷（TP）、径流中的总钾（TK）。结果表明，与CK相比，生物炭使SR提高了98.92-172.40%，SBR和UFR分别降低了72.69-77.00%和43.07-94.71%。随着生物炭施用量的增加，生物炭降低了UFR中的TC浓度，而SR和SBR中的TC浓度没有明显的规律。与CK相比，B15、B30和B60处理下SR中的TN浓度降低，而SBR中的TN浓度升高，而UFR中几乎没有差异。没有显着性差异（P > 0.05）四个处理中的TP浓度。通过SR输出的TC、TP和TK占主导地位，占总负荷的60%~97%。但SR中TN输出负载较低，其负载占总输出负载的比例不足30%。本研究得出的结论是，与未施用生物炭的情况相比，生物炭处理使 SR 提高了 98.92-172.40%，但使 SBR 和 UFR 降低了 43.07-94.71%。生物炭的施用增加了TC、TP和TK的总输出负荷，但降低了TN的总输出负荷。总之，生物炭改变了岩溶土壤的孔隙结构，降低了土壤的入渗能力，最终增加了 SR 并降低了 UFR。更重要的是，生物炭的应用对于调节水、土壤、以及岩溶斜坡地表和地下流道的养分流失。此外，生物炭减少了TN损失。研究结果可为研究生物炭对喀斯特山区土壤侵蚀和养分输出的影响机制提供理论依据。