Rates and timing of nitrogen application for obtaining the economic grain yield, under no-tillage on cerrado of Mid-North region of Brazil

Abstract

The objective of this work was to identify the nitrogen (N) rates to obtain the economic grain yield, on cerrado soil in Mid-North region of Brazil. The experiments were carried out during the growth season of 2001/2002, in Baixa Grande do Ribeiro, PI and São Raimundo das Mangabeiras, MA, counties. Four levels of N (0, 60, 120 and 180 kg.ha^-1) and two forms of nitrogen application (1/2 in foundation + 1/2 for occasion of sixth leaf, and 1/3 in foundation + 1/3 for occasion of fourth leaf + 1/3 for occasion of the sixth leaf) were evaluated concerning grain yield in soils under no-tillage. The experimental design was randomized blocks, with four replications. The treatments were combined in an uncomplete factorial 2x3 + 1 (control: 0 kg.ha^-1 de N) . In Baixa Grande do Ribeiro, the response of grain yield to levels of N was quadratic, yielding  5,723.1 kg.ha^-1 , with the economic doses of 67 kg.ha^-1 of N. In São Raimundo das Mangabeiras, the response of grain yield to levels of N was linear, yielding 7,691.8 kg.ha^-1 with 180 kg.ha^-1 of  N.