Efeito do pré-cultivo de adubos verdes na produção orgânica de brócolos (Brassica oleraceae var. italica) em sistema de plantio direto

Abstract

This study was carried out under field conditions at the Agroecological Integrated Production System (AIPS) to chose the best option of cover crop to much the soil suface for broccoli organic managed in no-tillagem systems. The experiment was set in a randomized blocks design with four treatments during two years in the same field location. In the first year the treatment used was, sorghum; millet; sum hemp and weeds as control. In the second year was replaced to a misture sum hamp and sorghum to optimize the benefits of utilization of legume. The cover crop was cut and left in the soil surface as mulch to provide a thick residue that release nutrients and suppress growth of weeds and prove a best environment to broccoli development. This study included evaluation relating with biomas production, concentration and accumulation of nutrients at cover crop; decomposition rates and nutrients released at straws; weed community before and after cover crop was cut; broccoli marketable production and nutrients concentration at index leaves of broccoli. Sorghum; millet; sum hemp and sorghum plus sum hemp mixture production of straw was plus than 7,0 Mg ha-1 dry mass and proved a good much with the slowest decompositions rates. The decomposition rate and nutrient release rate was fast in weeds and slower in grass than legume. The mixture grass-legume has a intermediate rate whem is compared with sorghum and sun hemp monoculture. Legume accumulation plus Ca and grass plus K and P. The faster nutrient releases from mulch was K and the lowest was Ca, while N, P and Mg was variable among treatments. Legume grass mixture can improve quality of mulch because they have different root ability to nutrient up take. The straws of sorghum, millet, sum hemp and sorghum plus sum hemp mixture restring weed growth and show that is possible to reduce additional control measures. The index leaves of broccoli was able to show differences in nutrients up take only to K at the first year, when it was higher in broccoli planted in millet and sorghum residues, but at the second year N and P was higher in leaves of broccoli planted in sum hemp and mixture of sorghum plus sum hemp residue. At the broccoli marketable yield was better in cover crop than weeds. In the second year the mixture grass-legume effect in broccoli growth was similar to legume alone.