Parcelamento da adubação nitrogenada em diferentes cultivares de girassol

Abstract

Nitrogen fertilization is the management that most limits development and production in the sunflower crop (Helianthus anuus L). The demand for the nutrient among cultivars of this species is different, even if using the same cultural treatments of cultivation. In order to test four types of nitrogen fertilization in three production variables of three sunflower cultivars and verify the performance of the cultivars under the experimental conditions, a randomized block design in a factorial scheme (3 x 4) repetitions. The treatments were composed of a combination of two sunflower cultivars, BRS 323 and BRS G54, from the Brazilian Agricultural Research Corporation (EMBRAPA), a Syngenta cultivar, SYN 045, and four forms of 60 kg.ha-1 of nitrogen, with as urea source: 100% at 20 days after sowing (DAS) (0-100-0-0); 30% at sowing and 70% at 20 DAS (30-70-0-0); 30% at sowing, 30% at 20 DAS and 40% at 40 DAS (30-30-40-0); 20% at sowing, 30% at 20 DAS, 30% at 40 DAS and 20% at 60 DAS (2030-30-20). The following variables were evaluated: seedling emergence, initial flowering, full flowering, physiological maturation, multivapitulation, plant height, stem height, stem diameter, stem size, weight of thousand achenes, number of leaves per plant, stem and yield of achenes. The obtained data were statistically evaluated, performing the analysis of variance and according to the result of this were performed mean tests. The cultivar that presented greater adaptability to the conditions where the experiment was performed was BRS 323, being recommended its cultivation in the region. It is indicated that the recommended nitrogen dose, 60 kg.ha-1, is applied 30% at the time of sowing and 70% at 30 DAS.