Manejo da adubação nitrogenada em função dos estádios fenológicos da cultura do girassol

Abstract

The sunflower crop to adapt to different environmental conditions, and in recent years, it has been presented as an alternative for crop rotation and succession, because of this greater tolerance to conditions of water deficit, lower number of incidence of pests and plants diseases, in addition to the cycling of nutrients. However, the management of nitrogen fertilization is a limiting factor for its sunflower growth and your achene production. Because of this, the objective was to evaluate the vegetative and productive development of sunflower, as a function of the management of nitrogen fertilization at different phenological stages of the crop. The experiment was conducted in two periods, in the 1st harvest (2020/2021) and 2nd harvest (2021). The cultivar used was BRS 323, an early cycle single hybrid. The treatments consisted of five diferents times of nitrogen application, being applied 60 kg ha-1 of N in V0 and incorporated and in the other treatments V2, V4, V6 and at 35 days after emergence, the subdivision was made, being: 30 kg ha-1 of N at sowing and 30 kg ha-1 of N when the plants reached the phenological stage V2 with two true leaves, V4 with four true leaves, V6 with six true leaves and 35 days after emergence. The experimental design used was randomized blocks, each experimental unit consisted of 5 lines, spaced at 0.70 m from each other and the sowing density of 45000 plants ha-1 . The variables evaluated were: number of leaves, plant height, flowering, stem diameter, chapter diameter, number of achenes per chapter, mass 1000 achenes, productivity and nitrogen content. The results were submitted to conventional statistical analysis through correlation and principal component analysis to assess the relationship between the variables and the crops under study. The application of 100% of the dose of N in the sowing, incorporated, expresses the best efficiency of the application of urea.