Apart from the soil tillage system, the soil surface conditions that govern the rainwater erosion process change during growth of the corn crop. At the same time, the physical conditions of the soil surface that govern soil losses are different from those that govern water losses by erosion. The hypothesis of this study is that these changes occurring during the growth of the corn crop reduce soil losses but do not reduce water losses by erosion. Based on that, this study was carried out with the aim of evaluating the effect of different soil surface physical conditions, created by tillage methods, on soil and water losses by water erosion (caused by simulated rainfall), at three moments of the corn crop. The study was developed in the field at the EEA/UFRGS in the municipality of Eldorado do Sul, Rio Grande do Sul, Brazil, on an Argissolo Vermelho distrófico típico (Acrisol) with sandy clay loam texture in the A horizon, and 0,08 m m-1 average slope. The treatments under study, established on (newly harvested) black oat crop residues were: conventional tillage (one plowing+two diskings - A+2G); reduced tillage 1 (one chiseling+one disking - E+G); reduced tillage 2 (one chiseling only - E); no-tillage 1(no-till planter-fertilizer equipped with furrowing shafts or shanks for placing fertilizer at a 12 cm soil depth - SDf); no-tillage 2 (no till planter-fertilizer having no shafts or shanks, but equipped with double-disk openers for placing the seeds at a 5 cm soil depth - SDd); and control treatment (conventional tillage - one plowing+two diskings but in continuous fallow - unit or standard plot - T), followed by sowing the corn (except for treatment T). Soil and water losses by erosion were evaluated by applying three simulated rainfalls (rotating-boom simulator), each of them at an intensity of 64 mm h-1 of 120 min duration, at the following moments of the corn crop: immediately after sowing; at 45 days; and at 116 days after sowing. Soil surface roughness created by chiseling delayed surface runoff and increased water infiltration, considerably reducing water loss by erosion, while surface cover by crop residues significantly reduced soil loss. The no-till planter equipped with furrowing shafts or shanks disturbed the soil more than the one without them (equipped with only double-disk openers), decreasing water loss by about 35 % and minimizing soil loss. In the conventionally tilled and planted soil, due to both the natural reconsolidation process and the gradual soil cover offered by corn plants, soil loss by erosion was greater at the beginning of cropping, while water loss was greater at the end.
simulated rainfall; no-tillage; chisel-plowing; soil surface roughness; soil surface cover; soil loss; water loss
