Organic matter is considered the soil attribute most sensitive to the changes triggered by the management systems. The objective of this study was to evaluate the effect of nine years using three soil tillage systems -conventional tillage, reduced tillage and no tillage- on soil chemical characteristics of a Humic Cambisol in southern Brazil. Soil samples were collected in September 1996 at depths of 0-2, 2-5, 5-10, 10-15, and 15-20 cm, and analysed for C and N contents in total organic matter and its coarse fraction and for other soil chemical characteristics. Soil management with no tillage and reduced tillage increased C and N at the soil layer of 0-20 cm in comparison to the conventional tillage. With reduced tillage, the increases of C and N in the total organic matter were of 12% (6.3 t ha-1) and 17% (593 kg ha-1), respectively, in relation to conventional tillage. With no tillage, the increases of C and N in total organic matter were of 17% (8.5 t ha-1) and 24% (808 kg ha-1), respectively, in relation to conventional tillage. The increases of C and N in coarse organic matter (> 53 ∝m) with reduced tillage were of 85% and 45%, respectively, in relation to conventional tillage. With no tillage, the increases of C and N in coarse organic matter were of 275 and 230%, respectively, in relation to conventional tillage. A close relationship was observed between effective CEC and soil pH and C content [CEC = -13.53 + 3.58 pH + 3.51 C(%); R² = 0.76], confirming the dependence of CEC on soil organic matter. No tillage resulted in a stratification of Ca, P and K along soil depth, as compared with reduced tillage and conventional tillage, while pH and Al were not affected by the soil tillage treatments. None of the treatments resulted in any chemical limitation for crop development and productivity.
soil tillage; no tillage