Crop residue in direct contact with the soil surface is very effective in dissipating the energy of raindrop impact on soil, being also a physical barrier against interrill overland flow. The presence of these residues may strongly affect the interrill soil erosion process. A study was carried out with the objective of evaluating the relationship between interrill erosion and amounts of crop residue in direct contact with soil surface and to verify the differences in this relationship for corn and wheat residues. An experiment was conducted at the Forest and Soil Conservation Research Center of FEPAGRO, in Santa Maria, RS, on a Paleudult sandy loam soil. Experimental interrill plots of 0.50 x 0.75 m, with the largest dimension parallel to the direction of land slope of 0.17 m m-1, were arranged in 4 completely random blocks. Residues of corn and wheat chopped in pieces of about 7.5 cm were distributed over the plots on freshly tilled soil, at amounts of 0.00, 0.05, 0.10, 0.20, 0.40 and 0.80 kg m-2. Simulated rainfall was applied at a mean intensity of 67 mm h-1, during 90 minutes. There was a significant variation of interrill soil and water losses with the time of rainfall and with amount of crop residues. However, there was no variation with the type of residue. The relationship between interrill soil loss and amount of residue in direct contact with soil surface fitted well to an exponential equation. This exponential model is recommended to estimate the subfactor interrill soil cover by residues in direct contact with the surface, because it is easy to use and obtain measurements.
soil erosion by water; interrill erosion; soil cover; residue ground cover