Ferrugem asiática e produtividade da soja sob doses de potássio na região de Dourados-MS na safra 2007/08

Abstract

Among the main factors that limit the productivity, profitability and success of soybean production there are distinguished the diseases, particularly asian soybean rust, which has been considered one of the most important cause of soybean losses. Potassium is cited as one that has a major impact on soybean diseases due to fact that is crucial in many metabolic reactions. Thus, the objective this research was to evaluate the effect of potassium fertilization on incidence and severity of asian soybean rust, nutrient content on leaves, and productivity under field conditions in Dourados – MS, Brazil. The experiment was lead in Dourados-MS in Oxisol (Typic Haplustox), cultivated on no-tillage system on corn mulching. The experimental design chosen was Randomized block with six replications, and the treatments were arranged in split-plots (plots - five K2O rates (0, 40, 80, 120 and 160 kg ha-1) using as fertilizer the potassium chloride (KCl) and subplots (presence and absence of fungicide sprays with azoxystrobin+ciproconazole)). The nutrient content in the leaves, incidence and severity asian soybean rust, productivity and weight of 100 grains were analyzed. Potassium fertilization had no effect on nutrient content. Fungicide application was essential to reduce the incidence and severity of asian soybean rust and increase productivity and weight of 100 grains. Without fungicide application, productivity was reduced 22% (574.1 kg ha-1), and the weight of 100 grains decreased 18.6%. The rate of 80 kg ha-1 K2O in presence of fungicide application was promising to reduce the deleterious effects of asian soybean rust on incidence of the middle third and upper third and severity in the upper third of the soybean plants. When fungicide was not sprayed rates greater than 120 kg ha-1 of K2O were needed in order to achieve higher yields.