Yield of castor bean fertilized with sewage sludge and potassium and magnesium sulphate

Abstract

The aim of this study was to evaluate the yield and nutrition of castor bean in response to fertilization with sewage sludge and potassium (K) and magnesium (Mg) sulphate. The experiment was carried out from January to July 2011. The treatments, in a randomized block design with three replicates, in a Nitosol, corresponded to a factorial scheme (2 x 4 +1): two doses of K and Mg sulphate combined with four doses of sewage sludge (0, 2.60, 5.20 and 10.40 t ha-1, dry basis), applied based on its nitrogen (N) content and the N requirement for the crop and an additional treatment with NPK. The castor bean grain yield fertilized with sewage sludge did not differ from conventional fertilization, with the maximum value achieved at a dose of 7.5 t ha-1 of sewage sludge. The fertilization with sewage sludge increased zinc and copper levels in the soil to values close to or higher than those in conventional fertilization, without any influence on the concentrations in the leaf. Fertilization with K and Mg sulphate increased the levels of these cations in the soil without affecting the concentrations in the leaves. The fertilization with sewage sludge increased the contents of organic matter, sulfur, zinc, iron, copper and boron in the soil, and manganese and boron in castor bean leaves.