Água residuária da suinocultura nos teores de cobre e zinco em sistema de plantio direto a longo prazo

Abstract

The swine wastewater (SWW) application in agriculture comes as an ancient, popular, and attractive alternative over disposing of it into waterbodies, since it has been an additional treatment for such waste. It also works as a source of water and nutrients to the soil-plant system. However, high concentrations of copper and zinc in these wastes have called some attention to environmental safety. In this context, this research aimed at evaluating the effects of a long-term SWW application on copper and zinc contents in soil-plant system in an area of annual crop. The research analyzed a database from six experiments which aimed at evaluating the effects of SWW applications associated with rates of chemical fertilizer (CF) on soil characteristics under corn, black oats, and soybeans croppings. The experiments were carried out from 2006 to 2009 at the Agricultural Engineering Experimental Area (NEEA), in Cascavel, PR, Brazil. Chemical characterization of soil, at 0.6 m layer, was done before carrying out the treatments and after managing each crop, totalizing six samples during the time of this research. The analyzed parameters were: pH, organic matter, cation exchange capacity, copper, and zinc rates. Analyses of leaves tissue for copper and zinc were determined on corn, black oats, and soybeans crops. The experimental design was in randomized blocks, in triple-factorial with four rates of SWW (0, 100, 200, and 300 m3 ha-1 during the period), two levels of chemical fertilization (with or without CF), and six time periods, with three replications. There was an increase in all parameters, especially an accumulation of copper and zinc on soil profile after successive SWW applications. Copper and zinc rates in the analyzed soil, according to agronomic recommendations, were high. However, they did not exceed the maximum level allowed by environmental regulations. The results of the analyses of the leaves tissue showed that the plants presented levels of copper and zinc within the range of agronomic recommendation. It can be concluded that, in a long term, SWW application favors the accumulation of heavy metals in soils and plants, which can enhance environmental impacts due to waterbodies contamination and their passing to the food chain.