Fontes e métodos de aplicação de nitrogênio em feijoeiro irrigado submetido a três níveis de acidez do solo

Abstract

In conservation tillage systems, where the revolving of the superficial layer does not occur, the nitrogen fertilizers and lime have been applied in the soil surface, however little is known about this practice on irrigated bean yield. The objective of this study was to evaluate, for three consecutive years, the effect of top dressing of 80 kg ha-1 of N, sources of urea or ammonium sulfate, incorporated or distributed in the soil surface, in three levels of soil acidity developed by the application of 0, 3.5 and 7 Mg ha-1 of lime, compared with on N application. Half of the N was applied on the 15th day after the plant emergency and the other half on the 30th day after the plant emergency. The experimental design was randomized split plot, being the lime doses assigned to the plots and the treatments of N to the subplots, with three replications. The treatments were evaluated based on grain yield, N uptake, soil pH and economical criteria. The average grain yield increased due to the application of top dressing of N in 13%, not having, in the average of the three crops, differences between urea and ammonium sulfate, as well as between the application methods, superficial and incorporation to the soil. There was linear positive answer to the lime and no significant interaction between N and lime, in relation to grain yield and N accumulation in the plant. The successive N applications reduced the pH in 0.2 units at 0-10 cm depth. The application of N urea source in the soil surface, followed by irrigation, is the most economical option of nitrogen fertilization for the irrigated bean crop.