Desempenho de cultivares de girassol irrigado sob adubação nitrogenada e boratada.

Abstract

Sunflower (Helianthus annuus L.) is a highly adaptable plant to Brazilian soils and climate conditions and can be grown from north to south of the Country, however, being a demanding culture nutritionally, Brazilian soils mineral deficiency is the factor limiting their more production. Among the essential nutrients for its development it is known that nitrogen (N) and boron (B) exert significant roles in the growth and development of culture, and its deficiencies promote nutritional disorders to the plant, reflecting negatively on its yield. In this context, it is aimed to evaluate the performance of two sunflower cultivars, Helio 250 and Helio 251, under conventional fertilization function with nitrogen and boron under conditions of field and vegetation house in the semiarid of Paraíba State. The study consisted of two experiments to sunflower performance studies to nitrogen and boron fertilization. The first experiment was conducted in the field and constituted of three replicates of four nitrogen rates (30, 60, 90, and 120 kg ha-1) and four boron doses (1, 2, 3, and 4 kg ha-1) for the two sunflower cultivars; the second experiment was conducted in a greenhouse and had four nitrogen rates (33.33; 66.66; 100; and 133.33 mg kg-1), four boron doses (1, 2, 3, and 4 mg kg- 1) in both cultivars of sunflower and with three replicates. In both experiments were analyzed the vegetative growth, the stages of reproductive development, phytomass production, income and the efficient use of nitrogen and boron. The duration of sunflower phenological stages were not affected by N or B. The vegetative growth, the productive yield and the accumulation of dry phytomass in the various plant organs were directly correlated to the amount of N available in the soil. High concentrations of B did not result in significant gains in growth or production. The maximum N and B use efficiencies were obtained at lower doses tested in this study. The cv. Helio 251 was more efficient in the production of phytomass, while the cv. Helio 250 excelled in the production of oil.