Response of dissolved organic carbon loss in agricultural runoff to tillage measures and rainfall characteristics in Southwestern China

Agricultural runoff mobilizes a significant amount of dissolved organic carbon (DOC) from soils into aquatic systems, posing the dual threat of altering the distribution of soil organic carbon and causing water pollution. Rainfall characteristics and tillage measures are key factors regulating the DOC loss via runoff from sloping farmland during the agricultural production process. In this study, the DOC characteristics of surface runoff, interflow (0–20 cm) and interflow (20–40 cm) in sloping maize farmland under three tillage measures (conventional tillage, cross-ridge tillage and downslope ridge tillage) were investigated. The results showed that surface runoff was the primary pathway for DOC in the sloping cropland. The concentration of DOC in surface runoff decreased gradually as the runoff volume increased. There was a change point for the DOC concentration in the interflow, with the threshold ranging from 2.25 to 11.4 L of interflow volume. The DOC in surface runoff was greatly influenced by rainfall, whereas the DOC in interflow was greatly influenced by rainfall duration. Runoff and DOC loss were the largest during long-duration, heavy rainfall and medium rainfall intensity of C pattern. Downslope ridge tillage exacerbated DOC loss in surface runoff, cross-ridge tillage effectively reduced the DOC loss in runoff. This study clarifies the response of DOC loss in runoff to tillage measures and rainfall characteristics under different loss pathways. Such insights are crucial for slowing the loss of organic carbon in sloping croplands, mitigating agricultural water pollution, and promoting sustainable agricultural development. • The change points of dissolved organic carbon concentration were determined. • The runoff and dissolved organic carbon loss were the highest under C rainfall pattern. • Cross-ridge tillage can effectively reduce dissolved organic carbon loss. • Surface runoff was the primary pathway of dissolved organic carbon loss. • The contribution of rainfall to dissolved organic carbon loss was quantified.