Water erosion influenced by surface and subsurface soil physical conditions resulting from its management, in the absence of vegetal cover

Different management practices lead to distinct surface and subsurface soil physical conditions, which in turn result in different levels of rainfall erosion. In this context, a 5.5 year field erosion-study was conducted with the objective of studying the effects of both tillage and cropping systems and forms of crop residue management on some surface and subsurface physical soil conditions and their influence on rainfall erosion. For this purpose, rainfall was simulated on a severely degraded, sandy loam Paleudult with 0.08 m m(-1) slope-steepness. Treatments consisted of corn and black oat cultivation, both under no-tillage and conventional tillage (the latter with incorporation or removal of crop residues), and no-plant cultivation under conventional tillage (control). For all treatments, the soil was freshly-tilled or consolidated, without residue cover, when the erosion tests were performed. Ten rainfall tests were imposed with the rotating-boom rainfall simulator at a constant intensity of 64.0 mm h(-1) during 90 min, short after the harvest of one crop and the soil tillage (or no-tillage) for the subsequent crop. The continuous incorporation of crop residues into the soil improved its structure and reduced soil losses by nearly 3/4, compared to residue removal. Due to the newly-created surface roughness of the soil, the conventional tillage treatments presented higher water retention and infiltration capacity. This effect delayed the surface runoff and decreased water losses in comparison to the no-tillage treatment, regardless of plant cultivation and incorporation, or removal of crop residues. However, conventional tillage without plant cultivation in spite of a surface roughness similar to that under cropping, presented the highest soil loss in the study. The highest water losses were found in the no-tillage treatment, despite the recovery of the soil structure by crops. The soil losses in this treatment were similar to those observed under the conventional tillage with removal of residue, and intermediate to the conventional tillage with incorporated residues and the conventional tillage without plant cultivation. Soil loss after corn cultivation was virtually twice as much that after black oats, regardless of soil tillage and the incorporation or removal of crop residues. But, the water loss was only slightly higher. Results confirmed that surface and the subsurface physical soil conditions created by the tillage system that affect soil losses by rainfall are different from those that influence water losses by the same event.