Modification of a rainfall simulation procedure at runoff plots for soil erosion investigation

A modification of a rainfall simulation procedure at runoff plots for the study of erosion is suggested. It is based on the (1) physically substantiated erosion parameter of simulated rainfall A, (2) the new erosion index for natural rains AI derived from the erosion parameter A, and (3) USLE and RUSLE equations. To simplify the testing procedure and interpretation of the measured data, we use rainfall of permanent intensity I, drop size, and rainfall velocity V. To study the influence of any factor (or their combination) on the soil loss, the experiment was performed at several runoff plots, one of which was a control (fallow soil, and soil tillage performed along the slope). According to the measurement results, a graph of the dependence between the cumulative soil loss and the AI index was compiled that fits the linear regression equation. Thus, the derived equations are also valid for natural rains. The critical values of AI (cr) upon which the runoff and soil loss start are determined from these equations. The soil erodibility factor is calculated from the equation obtained for the control plot using the relief factor of the RUSLE equation. The influence of the studied factors on soil erosion is assessed from the comparison of equations obtained for the appropriate sites and the control. Upon the infiltration study, the water discharge is measured until its stabilization, when the steady infiltration velocity is reached. The following investigation results are cited as examples: (1) the influence of the initial soil moisture, the soil mulching with straw, and the plant cover on the soil loss; (2) application of the obtained experimental data for assessing the average annual soil loss from natural rains; and (3) the relationship between the infiltration and the rainfall erosivity index AI.