Applicability of USLE to predict soil erosion under sub-tropical climate of India

Soil loss was directly measured on four run off plots, 25 min length along 2.35% slope having 4 treatments of along the slope and contour till aged without and with N₆₀ P₃₀ fertilization on crop of Jowar millet (Sorghum vulgare Pers.) for 3 years under subtropical climate of northern India. Soil loss was at the same time predicted from USLE by estimating the values of R from rainfall by the equation R=71.9+0.361x rainfall, K from soil erodibility nomograph and LS from topographic factor nomograph of Wischmeier and coworkers. C factor for Jowar was taken as 0.629 and P factors for contours and fertilization were computed from the runoff soil loss data. As a mean of 3 years data, soil loss from run off plots measured 13.63 t ha⁻¹ for along the slope without fertilization, which was reduced to 6.59 t ha⁻¹ on contouring. On fertilization, soil loss was measured as 10.49 t ha⁻¹ along the slope, which was reduced to 5.34 t ha⁻¹ on contours. The predicted soil loss from USLE averaged for 3 years was found 29% higher than the observed soil loss from runoff plots in all combinations of along the slope, contours, with and without fertilization. Year to year deviation was ranged between 25 to 32%. The deviation was traced to 29% higher nomograph predicted values of K over the experimental values from run off plots. The study emphasizes the need to standardize the K and LS factors against runoff soil loss experiments to enhance the usefulness of USLE for prediction of soil erosion under the soil and climatic conditions of India.