Soil, nutrient and organic matter losses in a Red-Yellow Podzolic under simulated rainfall

The present work was carried out in a kaolinitic Red-Yellow Podzolic at Vicosa, State of Minas Gerais, Brazil, aiming to evaluate the effect of soil cover under simulated rainfall at an intensity of 60 mm V on soil, nutrient and organic matter losses, and microstructural effects. The experimental area was set up in a downslope cultivation (average slope of 9.5%), with five experimental units (2.0 x 2.0 m) with a Bidim soil cover of 0, 20, 40, 80 and 100%. Six successive rainfall applications were made at 12 hours regular intervals, collecting the resulting soil materials after each test. The soil losses were higher than 11 t ha(-1) in treatments with cover ranging from 0 to 40%, and about 5 t ha(-1) with 80% cover, and no losses were observed in the 100% Bidim cover. The nutrient losses followed the order Ca>Mg>K>P and were correlated to organic matter. The organic matter fractionation revealed a residual concentration of humin and selective loss of soluble forms with runoff. A heterogeneity between the upper and lower parts of the experimental unit, attributable to erosion, was observed. The macroporosity estimated by micromorphology at the 10-20 cm depth was consistently higher in the upper part of the unit, suggesting clay migration and porosity loss under simulated rainfall. Except for the 100% cover, all others showed the development of depositional crust, whereas the most exposing treatments also showed the presence of erosional crust, at the end of the tests.