A method for estimating the interaction depth of surface soil with simulated rain

• We present the relationships between each impact factor and the effective depth of transfer.
• We give an equation of estimating the effective depth of transfer with knowing the impact factors for loessial soil;
• We provide an estimate method for calculating the contribution of each impact factor on the effective depth of transfer.

The effective depth of transfer (EDT) between surface soil and runoff was determined by varying the physical properties of the soil, rain intensities (RIs), slope gradients, initial water contents, and soil amendment. The effects of these factors on the EDT were quantified with simulated rain. The EDT increased (0.12–1.09 cm) with an increase of RI and slope gradient (0–30°), and the effect of RI was attributed to increases in raindrop impact and runoff energy, which enhanced mixing in the surface soil. Slope gradient accelerated the velocity of water flow and decreased the stabilities of soil particles. The EDT increased from 0.192 cm to 0.709 cm with an increase in the initial water content, because variation in initial water content influenced soil infiltrability and detachability. The EDT exponentially decreased from 0.99 to 0.44 cm and from 0.86 to 0.36 cm for increasing amounts of dry granular and dissolved polyacrylamide (PAM), respectively, applied to the soil, likely because PAM improved the soil structure and prevented the formation of a crust. With soil-particle constitution ranging from silty clay to sandy loam, soil infiltration rate increased, and the EDT exponentially decreased with parameters Kd and Kp. We obtained an equation describing the combined effects of the various factors on the EDT by regression analysis. Analyses of root mean square errors and the coefficients of multiple determination indicated that calculated values fit the experimental data very well. This relationship provided a method of estimating the EDT and improved the prediction of the transport of adsorbed chemicals in solution, because current models of chemical transport use fixed values.