The objective of this research work was to evaluate black oat decomposition and release of nutrients. The experiment was carried out during the 1998 cropping season in an experimental area located in Marechal Candido Rondon, Parana State, Brazil. A randomized block design with four replications was used. The cover crop was rolled over thirty days after emergence. The persistence and release of nutrients were evaluated at 0, 13, 35 and, 53 days after rolling and desiccation. The decomposition rate of oat residue was constant during this period (remaining 34% of the initial amount) and inversely proportional to the C:N ratio that showed an initial value of 34 and a final value of 50. Most K was released soon after oat management, remaining only 2% of the initial content in the last sampling time. N, P, Ca and S were gradually released, and in the last evaluation the remaining amount of these nutrients was 55, 42, 48, and 47% of the total accumulated amount, respectively. Compared to other plant nutrients, K followed by N were the nutrients available in higher amount in the soil, reaching maximum release speed between 10 and 20 days after rolling and dessication of black oat.
