Matéria orgânica e aumento da capacidade de troca de cátions em solo com argila de atividade baixa sob plantio direto

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 15.2mmolckg-1 and the potential (pH 7.0) CEC increased 20.7mmolckg-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.