Agronomic performance of bean subjected to nitrogen levels at sowing and topdressing/ Desempenho agronomico do feijoeiro com doses de nitrogenio em semeadura e cobertura

Appropriate management practices and higher nitrogen doses have led to substantial increases in grain yield of common bean, however in winter crop and under irrigated conditions few studies report the interference of nitrogen doses at seeding and in topdressing on the grain production. The study aimed to evaluate the effect of adding increasing doses of nitrogen at sowing and topdressing on the agronomic characteristics of bean irrigated during winter in the northern part of Minas Gerais state. For this purpose a 4 x 4 factorial design was used consisting of four identical doses of nitrogen at sowing and topdressing (0, 40, 80 and 120 kg [ha.sup.-1]). The following characteristics were evaluated: initial stand, final stand, number of grains per pod, pods per plant, mean weight of 100 grains and grain yield. No significant effect (p > 0.05) was obtained between N rates at seeding and/or topdressing for the number of grains per pod and weight of 100 grains. Considering only the addition of N at sowing, the number of pods per plant and grain yield increased with increasing dose up to '20 kg [ha.sup.-1] N. Despite the interdependence of N rates in seeding and topdressing, major increases in grain yield were obtained with the addition of N at sowing. Key words: common bean, production components, grain yield Praticas de manejo adequadas e o aumento das doses de nitrogenio tem propiciado incrementos substanciais na producao de graos do feijoeiro comum; no entanto, em cultivos de inverno e irrigado existem poucos estudos relatando a interferencia do uso de doses de N em semeadura e cobertura na producao de graos. O estudo teve o objetivo de avaliar o efeito da adicao de doses crescentes de nitrogenio em semeadura e cobertura no desempenho agronomico do feijoeiro irrigado no periodo de inverno no Norte do Estado de Minas Gerais. Para tanto, utilizou-se o esquema fatorial 4 x 4 consistindo de quatro doses identicas de nitrogenio em semeadura e cobertura (0, 40, 80 e 120 kg [ha.sup.-1]). O delineamento estatistico utilizado foi em blocos casualizados com tres repeticoes. Foram avaliadas as caracteristicas: estande inicial, estande final, numero de graos por vagem, vagem por planta, peso medio de '00 graos e rendimento de graos. Nao se obteve diferenca significativa (p > 0,05) entre doses de N em semeadura e/ou coberta para o numero de graos por vagem nem para o peso de 100 graos. Considerando apenas a adicao de N em semeadura, o numero de vagens por planta e o rendi