Swine wastewater application on copper and zinc contents in system for long-term tillage

A utilizaÃÃo de Ãgua residuÃria de suinocultura (ARS) em solos agricultÃveis, ao invÃs de realizar a disposiÃÃo deste resÃduo nos corpos dâÃgua, tem sido uma alternativa antiga, popular e atrativa pelo fato de complementar o tratamento dos dejetos e servir de fonte de Ãgua e nutrientes para o sistema solo-planta. Entretanto, a constataÃÃo de altas concentraÃÃes de cobre e zinco nestes resÃduos vem causando preocupaÃÃo com relaÃÃo à seguranÃa ambiental. Nesse contexto, este trabalho visa avaliar os efeitos do uso prolongado de ARS sobre os teores de cobre e zinco, no sistema solo-planta, em Ãrea de cultivo anual. O trabalho consiste na anÃlise de um banco de dados oriundo de seis experimentos que visavam analisar o efeito da aplicaÃÃo de ARS associada a taxas de adubaÃÃo quÃmica (AD) nas caracterÃsticas do solo, sob cultivo de milho, aveia e soja. Os experimentos foram realizados entre os anos de 2006 e 2009, no NÃcleo Experimental de Engenharia AgrÃcola (NEEA), em Cascavel, PR. A caracterizaÃÃo quÃmica do solo, na camada de 0,0-0,6 m de profundidade, foi realizada antes da aplicaÃÃo dos tratamentos e apÃs o manejo de cada cultura, totalizando seis amostragens no tempo. Foram avaliados os parÃmetros de pH, matÃria orgÃnica, capacidade de troca catiÃnica, e teores de cobre e zinco. AnÃlises de tecido foliar para os elementos cobre e zinco foram determinadas nas culturas do milho, aveia e soja. O delineamento experimental foi em blocos casualizados em esquema fatorial triplo com quatro taxas de ARS (0, 100, 200 e 300 m3 ha-1 no ciclo), dois nÃveis de adubaÃÃo quÃmica (com ou sem AD) e seis perÃodos de tempo, com trÃs repetiÃÃes. Observou-se aumento em todos os parÃmetros avaliados, destacando-se acÃmulo de cobre e zinco no perfil do solo apÃs sucessivas aplicaÃÃes de ARS. Os teores de cobre e zinco no solo, frente Ãs recomendaÃÃes agronÃmicas, encontraram-se altos, todavia, nÃo foram superiores aos limites mÃximos permitidos pela legislaÃÃo ambiental vigente. Os resultados da anÃlise de tecido foliar mostraram que as plantas apresentaram teores de cobre e zinco dentro dos limites de recomendaÃÃo agronÃmica. Conclui-se que aplicaÃÃes de ARS a longo prazo favorecem o acÃmulo de metais pesados no solo e nas plantas, o que pode potencializar impactos ambientais pela contaminaÃÃo dos corpos hÃdricos e a transferÃncia destes na cadeia alimentar.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 leavesâ 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 leavesâ 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