Delivery of Nutrients by Rill and Sheet Erosion in Agricultural Settings

Insight into the connection between erosional processes and nutrient exports is important for designing best management practices for sustainable agriculture and minimizing impacts on water quality. We present a mass balance approach to characterize rill and sheetwash erosion during a June 2004 thunderstorm event in Treynor, Iowa, USA. Observed sediment and radionuclide yields and soil profiles were modeled (Simulation of Rill and Sheetwash Erosion Model, SiRSEM) to solve for the areal extent and depth of rill and sheetwash erosion and from this information calculate sediment and nutrient losses. Results indicate that sheetwash eroded 98% of the plot to a depth of 0.078 mm and rills eroded 1% of the plot to a depth of 9 mm. Rill erosion contributed 54% of the total sediment yield. Results were compared to elevation changes determined by laser digital scanning. Topographic analysis indicated that rills eroded 1% of the plot to an average depth of 11 mm in accord with the SiRSEM results. Runoff yields for nineteen major nutrients and minor (micronutrients) was compared to yields predicted from SiRSEM results and concentrations of these constituents in the soil profiles. Excellent prediction accuracy was found for non-labile elements (>75% for ten of nineteen constituents). While sheet erosion accounted for 46% of sediment loss, it accounted for 45.6 to 51.2% of nutrient loss.