EDAPHIC CHANGES CAUSED BY DIFFERENT SOIL TILLAGE MANAGEMENTS CROP ROTATION SYSTEMS IN OXISOL UNDER SUBTROPICAL CONDITIONS

Soil fertility and organic matter were assessed after twenty years of implementation (1985 to 2005) on a typical Dystrophic Red Latosol soil located in Passo Fundo, State of Rio Grande do Sul, Brazil. Four soil tillage managements -1) no-tillage system, 2) minimum tillage, 3) conventional tillage using a disk plow, and 4) conventional tillage using a moldboard plow. and three crop rotation systems: I (wheat/soybean), II (wheat/soybean and common vetch/sorghum), and (wheat/soybean, common vetch/sorghum and white oats/soybean) were evaluated. As a control, soil samples were collected in a subtropical forest fragment adjacent to the experiment. A randomized complete block design, with split-plots and three replicates, was used. The main plots were formed by the soil tillage systems, while split-plots were composed the crop rotation systems. Higher levels of SOM, Ca and P were observed in the 0-5 cm layer for the SPD. The values of soil organic C, in the 020 cm layer was higher in NT as compared soil management tillage. Values of SOM observed in all soil management tillage and crop rotation systems were lower than in the forest. The values of P, and K were higher in the 0-5 cm layer, when compared to the ones observed in the 15-20 cm layer in soil management tillage. Values of pH, P, and K observed in the forest were lower and Al was higher than all soil management tillage and crop rotation systems.