Manejo da supressão e das frequências de irrigação e da fertirrigação nitrogenada na cultura do girassol

Abstract

Sunflower cultivation is an important alternative for irrigated agriculture in the Northeast Brazil region. It is explored in a rustic way and also causes little soil waste when compared to other cultures. The present work had as main objective to evaluate the effects of different frequencies, interval of irrigation suppression and nitrogen fertigation in sunflower harvest. The experiments were conducted in the meteorological station of the Federal University of Ceará in Fortaleza, Ceará, Brazil. The irrigation system used in the experiments was drip irrigation. The design used in Experiment I (irrigation suppression) consisted of a completely randomized block design, with six treatments and four replications. For Experiments II and III (irrigation frequency of fertigation with nitrogen, in this order), the design used consisted of a completely randomized block design, with five treatments and five replications. The treatments adopted were: 45 days after sowing (DAS); 52 DAS; 59 DAS; 66 DAS; 73 DAS and 80 DAS. For Experiment II, the applied treatments were: F2 (irrigation every 2 days); F4 (irrigation every 4 days); F6 (irrigation every 6 days); F8 (irrigation every 8 days); F10 (irrigation every 10 days). For Experiment III, the treatments were: FN2 (2 irrigations in cycle); FN4 (4 irrigations in cycle); FN8 (8 irrigations in cycle); FN16 (16 irrigations in cycle) and FN32 (32 irrigations in cycle), respectively. The following variables were analyzed: mass of a thousand seeds (M1000S), productivity (PROD), capitulum (inflorescence flower) dry mass (PS CAP), stem dry mass (PS Caule), leaf dry mass (PS Folha), seed oil content (TOS), potential of seed oil production (PPO), water use efficiency in seed production (EUAs), water use efficiency in oil production (EUAo) and leaf area (AR Foliar). In Experiment I, irrigation suppression affected M1000S, PROD, TOS and PPO for hybrid BRS 323 with linear polynomial mathematical adjustment for M1000S, PROD and TOS and quadratic adjustment for PPO with maximum yield of 2,370.30 kg ha-1 and irrigation depth of 528.87 mm in total period. In Experiment II, the F2 treatment resulted in better production for the studied conditions and 2,051.28 kg ha-1. In Experiment III, N application for maximum productivity was 19.27 irrigations per cycle with 2,261.99 kg ha-1 crop yield.