PARTICLE SIZE OF SEDIMENT YIELDED BY INTERRILL EROSION UNDER DIFFERENT SOIL RESIDUE COVER AND BY RILL EROSION ON A PALEUDULT SANDY LOAM SOIL

Abstract

Sediment particle size is a characteristic that affects the particles transportability and deposition in theerosion process. It is necessary to know the particle size distribution in order to build a model to predict the sedimentyield during an erosion process. Two field experimenta were conducted at the Forest and Soil Conservation ResearchCenter, from FEPAGRO, in Santa Maria, State of Rio Grande do Sul, Braz on a Paleudult sandy loam soil, to determinethe partido size distribution, from interrill and rill erosion processes. In the first experiment, residues of whcat and corowere applied as a surface cover on small interrillplots of 0.50 x 0.75 m, at amounts of 0.00, 0.05, 0.10, 0.20, 0.40 and0.80 kg/mi, in four replications on freshly tilled soil, with an average land slope of 0.17 m/m. A simulated rainfall withintensity of 67 mnifh was applied during 90 minutes, when runoff samples were taken to determine the sedimentparticle size distribution. In a second field experiment, concentrated flow rates of 10, 20, 30, 40 and 50 dm 2/min were applied during 40 minutes, on four replications of preformed 5 m long rills in a freshly tilled soil with an average landslope of 0.116 mim. The median size of the sediment yielded in the interrill soil erosion process decreased exponentiallywith the increase of the soil surface cover by crop residues. In the rill erosion process, the median size sediment particlesdecreased with the time from the beginning of the flow application. However, it was not observed any statisticallysignificant difference in the median size of the particle sediment with the increase in the flow rates. The median size ofsediment partido given by the Dsoíndex was 0.250 mm in the interrill erosion process and 0.325 mm in the rill erosionproccss.