CARACTERÍSTICAS QUÍMICAS DO SOLO AFETADAS POR MÉTODOS DE PREPARO E SISTEMAS DE CULTURA

A five year experiment established on a dark red Podzolic (Paleudult) soil at the University Experimental Station in Eldorado do Sul (State ofRio Grande do Sul, Brazil), was sampled in 1990. The objective was to determine the effect of soil tillage methods (conventional, reduced and no tillage) and crop systems: oats (Avena strigosa)/corn, oats + clover (Trifolium subterraneum/corn and oats + clover/corn + cowpea (Vigna unguiculata)) on total organic carbon (TOC) and other soil chemical characteristics Native grassland was sampled to represent original soil condition. Soil management affected TOC only in the surface layers of the soil (0-2.5 and 2.5-7.5cm). The highest soil TOC concentration was observed under no tillage and high addition residue crop systems The soil under no tillage and oats + clover/corn + cowpea crop system had 6.0 t ha -1 more TOC in the 0-17.5 cm soil layer, as compared to conventional soil tillage with oats/corn crop system. The soil cation exchange capacity at soil pH and at pH 7.0 followed the same changes as did TOC. The effect of the treatments on the pH, Al, Ca, Mg, K and P was mostly dependent on soil tillage, with uniform distribution with depth under conventional tillage and stratification under no tillage. The stratification of nutrients in the soil profile probably did not affect crop yields.