Soil management affects the organic matter stocks, and thus the CEC especially in low activity clay soils. The main goal of this study was to evaluate the long-term (21 years) effect of the no-tillage on soil organic carbon (SOC) stocks and its relationship with CEC increase in a clayey Oxisol (Hapludox), in Guarapuava (PR), Southern Brazil. No-tillage soil had only 2.63t ha-1 more SOC than conventionally tilled soil at 0-20cm, and the highest net accumulation occurred in soil surface layers (0-6cm). The low accumulation rate of SOC in the no-tilled soil (0,12t ha-1 yr-1) was related to the high physical stability of soil organic matter in this clayey Oxisol. Despite the small effect on SOC contents, the no-tilllage had an expressive influence on the CEC of 0-8cm soil layer. The effective CEC increased 15.2mmol c kg-1 and the potential (pH 7.0) CEC increased 20.7mmol c kg-1 in this soil layer, in comparison to conventional tillage system. The results support the positive effect of no-tillage on soil organic matter stocks and on CEC of tropical and subtropical soils with predominantly low activity clay minerals.
tropical soils; clay activity; soil management; soil quality
