Avaliação do efeito de doses e fontes de nitrogênio sobre variáveis morfológicas, interceptação de radiação e produtividade do girassol

Abstract

The objective of this study was to evaluate the effect of doses and sources of nitrogen on the morphological variables related to yield of two sunflower cultivars. The design was randomized blocks in a factorial design 5 x 2 x 2, with five doses of nitrogen (0, 40, 80, 120 and 160 kg ha-1), two sources of nitrogen (N) - conventional fertilizer (urea), with 44% N, and slow-release nitrogen fertilizer, with 26% N -, and two sunflower cultivars (Olisun 3 and Aguará 6) with three replications. We evaluated the plant height, leaf area index, global radiation interception, weight of a thousand achenes, achene diameter, yield and the estimate of chlorophyll content. Increasing doses of N promote an increase in the leaf area index, interception of global radiation, full flowering and sunflower yield, in a different way between cultivars. The use of slow-release nitrogen fertilizer provides higher leaf area index in the beginning of achenes filling, compared to the use of urea, from the dose of 120 Kg ha-1 N. The cultivar Olisun 3 shows greater leaf area index at full flowering and yield, from the doses of 80 and 120 kg ha-1 N, respectively.