Soil organic matter (SOM) constitutes the largest reservoir of carbon (C) and nitrogen (N) of the earth's surface. In agricultural soils, the organic fraction is of great importance in maintaining soil quality, while contributing a small fraction. Thus, the adoption of soil management practices and cover crops are important to promote the C and N accumulation in the soil and consequently improve its quality. The no-tillage system (NT) as conservation practice improves the soil structure, water infiltration and increases the contribution of C and N in the soil by deposition of crop residue on the surface. Thus, the soil is kept constantly covered by organic residuce of plants during their vegetative stage. This study aims to evaluate the stocks of C and N in the profile of a very clayey soil. The winter cover crops were grown under two management systems i. e., NT and conventional-tillage system (CT) in an long-term 26 years experiment. The experiment was started in the winter of 1986 in an Oxisol rich in aluminium, in southwestern Paraná at the Agronomic Institute of Paraná, with eight winter treatments (oat, rye, vetch, hairy vetch, wild radish, wheat, blue lupine and fallow). The collection of the soil samples was conducted in November 2012 at the following depths: 0–5, 5–10, 10–20, 20–30, 30–40, 40–60, 60–80 and 80–100 cm. A soil samples were collected under native forest from an area adjacent the experimental area serving as control. The soil C and N contents through the elemental analyzer. After 26 years of cultivation, the soil under NT showed the highest levels and stocks of C and N in the surface layers compared to the CT. However, below 20 cm and even upto 1 meter depth, the soil C and N stocks did not differ between the soil management systems. Regarding the use of different plant cover, these treatments did not differ in stocks of C and N in both management systems (NT and CT)
