Detailed studies on hydrology and sediment production are of great value to enhance the understanding and control of the water erosion process, with a view to more continuous and effective soil and water conservation practices. The purpose of this study was to develop specific (for each treatment replication) hydrograms (instantaneous runoff discharge versus time) and sedimentograms (instantaneous sediment concentrations in the runoff and instantaneous soil loss rates versus time), associated with water erosion in a soil under different crop sequences (winter and summer grass and legume species in no-till, mono and intercropped), with different physical conditions on the surface (untilled, recently-chiseled, previously-chiseled, and recently-disked soil, in addition to the presence and absence of crust and of full, little, and no cover by crop residues). The study was conducted in the field, at an experimental station of the Federal University of Rio Grande do Sul (EEA/UFRGS), in Eldorado do Sul (RS), Brazil, under simulated rain on an Ultisol with a sandy clay loam texture in the surface layer and 0.115 m m-1 average slope steepness. In the beginning of the study the soil had a high degradation degree. The rains (six in total, one for each erosion test) were applied with a rotating-boom rainfall simulator, at the designed rainfall intensity of 64.0 mm h-1 (in this study the observed rainfall intensities were used, ranging from 59.1 mm h-1 to 74.6 mm h-1) and duration ranging from 1 to 3 hours (determined to reach the runoff equilibrium condition in all erosion tests). It was observed that the hydrograms and sedimentograms were generally coherent with the conditions under which they were developed. Therefore, in most erosion tests the hydrograms differed more from one another than in the crop sequence treatments, opposite to the sedimentograms. The untilled soil surfaces with low roughness and cover, in general, provided hydrograms and sedimentograms with shorter start-up period and greater magnitude, regardless of the presence or absence of crust and type of crop sequence. The recently-tilled soil surfaces and those with medium and great roughness, in general, provided hydrograms and sedimentograms with longer start-up period and smaller magnitude, practically regardless of cover and type of crop sequence. The runoff from soil surfaces with complete cover was diminished and erosion eliminated, regardless of tillage and type of crop sequence. For the crop sequence with teosinte, the hydrograms and sedimentograms showed longest start-up periods and smallest magnitudes, followed by the ones with corn+cowpea and pearl millet, which differed little from each other. The replications of the treatments provided values of instantaneous runoff discharges that seemed more similar to one another and were more regularly distributed in time than those for the corresponding instantaneous concentrations of sediment and instantaneous soil loss rates. The obtained data were valuable for a better understanding of the variation commonly observed in the results of water erosion research developed in the field.
simulated rainfall; soil tillage; vegetal mulch cover; soil surface roughness; soil surface consolidation; soil water infiltration
