Effects of Soil Texture on Effective Mixing Depth and Solute Loss

［Objective］ The effective mixing depth is an essential parameter for quantifying and predicting solute loss. It is of great significance to quantify the effective mixing depth of texture-differentiated soils and investigate the response of effective mixing depth to soil erosion, and solute loss in the modeling of agricultural non-point source pollution. ［Methods］ The topsoils of five texturally distinct dry croplands in the Danjiangkou Reservoir Region were selected as the research object. The bromine ion tracer method was employed to quantify the effective mixing depth and its dynamic changes in texturally distinct soils. Simulated rainfall tests were conducted according to different bromine application depths [0 (soil surface), 0.5, 1, 2 and 5 cm] to determine the process of soil erosion and solute loss and analyze their responses to the effective mixing depth. ［Results］ Under the experimental conditions established in this study, the effective mixing depths during rainfall exhibited a range of 0.32—0.72, 0.11—0.57, 0.44—2.41, 0.11—1.04, and 0.13—0.28 cm. The effective mixing depths were found to be significantly affected by the clay content and soil texture (F=39.27, p<0.001). However, the effective mixing depths of different textured soils were significantly affected due to the differences in infiltration and flow production processes of different soil textures. Consequently, a significant linear relationship was not observed between the two. Furthermore, the effective mixing depth demonstrated a dynamic variation during the rainfall process, and exhibited a pronounced power function relationship with rainfall duration (R2>0.80). Furthermore, a notable distinction was observed in the soil erosion and sand production processes across varying effective mixing depths (F>12.068, p<0.001). Regression analysis demonstrated that the mean effective mixing depth exhibited a significant linear correlation with cumulative soil runoff and cumulative bromine loss (R2>0.92), as well as a significant exponential function relationship with sand production rate, sediment concentration, and cumulative sand production (R2>0.94). ［Conclusion］ The effective mixing depths of various textured soils exhibit notable disparities. A substantial linear or exponential correlation exists between the effective mixing depth, soil erosion, and solute loss indices. This correlation can be inverted through the runoff generation and sediment yield characteristics of the effective mixing depth, thereby enhancing the precision of the solute loss model.