Dinâmica de decomposição de resíduos culturais em sistemas rotacionados de manejo em um Planossolo Háplico do sul do Brasil

Abstract

Conservation management systems which include plants for ground covering in the winter in succession to summer commercial cultures are a vital strategy on the search of sustainability of the agroecosystem. This research aims to assess the potential production of biomass of cultivation systems and the process of decomposition of cultivation leftovers in low ground environments as subvention to the design of rotate management systems in a Typic Albaquult from the south of Brazil. The research has been conducted through field conditions; beginning in the autumn of 2005 and ending in the summer of 2006/2007, in the experimental area of Estação Experimental Terras Baixas da Embrapa Clima Temperado, in Capão do Leão, Rio Grande do Sul. The experimental lineation used was: random blocks with subdivided installments with three repetitions, set by five culture systems, two ground preparation systems (no-tillage – NT and conventional preparation – CP), and two doses of nitrogenous fertilization (with no mineral nitrogenous fertilization and the dose of N recommended for the summer grassy commercial culture). The cultivation systems assessed for the production of dry biomass and accumulation of nutrients were: ryegrass (Lollium multiflorum Lam) + birdsfoot trefoil (Lotus corniculatus)/fallow (R+B/F); fallow/ rotation (F/R); ryegrass + white clover (Trifolium repens)/ maize (Zea mays L) (R+WC/M); ryegrass/soybean (Glycine max L) (R/S) and ryegrass + birdsfoot trefoil/rotation (R+B/R); and two areas of reference (Ref. 1 and 2) cultivated with irrigated rice (Oryza sativa) (O). For the study of the process of decomposition of cultivation leftovers and nutrients release, the aspects assessed were: ryegrass, white clover, ryegrass + white clover, rice, maize and soybean. For the quantifying of dry biomass (BD) for winter species the gathering was done during the flowering while for summer species it was done during the milky stage of grain. The rotate management systems in a Typic Albaquult made it possible to deduce that cultivation systems with associate culture involving winter grassy and winter leguminous present a bigger amount of cultivation leftovers, which is a vital strategy as land coverage, cycle exchanges and also as a release of nutrients for summer commercial cultivations. In order to occur a higher utilization of nitrogen, phosphor, potassium, calcium and magnesium released by the winter cultivation leftovers to summer commercial cultures, in the systems that involve winter leguminous as antecessor plants, the period with the most need of the subsequent culture must coincide with the period of 30 days after chemist/mechanical handling of specie. If the system involves grassy, this period may occur 60 days after the handling.