SUMMARY
Sunflower is one of the most important oilseeds in the world, whose achenes are valued in several industrial chains, mainly for the extraction and processing of its oil. Although there is some information in the literature, the nitrogen (N) requirements for sunflower in semiarid conditions under irrigation are not yet clear. The experimental design used randomized blocks, with treatments in subdivided plots with four replications during two agricultural seasons. The N doses (e.g., 0, 30, 60, 90 and 120 kg ha-1) were assigned to the plots, and to the four sunflower cultivars used (e.g., Aguará 06, Altis 99, Multissol and BRS 122), which were planted in the subplots. The N doses for the maximum achene yields for the Multissol and BRS 122 cultivars were 81.8 and 86.6 kg ha-1, respectively, while N doses of 120 kg ha-1 produced the maximum achene yields for the Altis 99 and Aguará 06 cultivars in the 2016 crop season. In 2017, the Multissol and BRS 122 cultivars were given N doses of 100.7 and 92.8 kg ha-1, respectively, and the Altis 99 and Aguará 06 cultivars were each given an N dose of 120 kg ha-1 of N. The fertirrigated doses of maximum economic efficiency of N were 60 and 70 kg ha-1 for the Multissol and BRS 122 cultivars, respectively. For the oil yields, the maximum N doses of 78.0 and 86.7 kg ha-1 for the BRS 122 and Aguará 06 cultivars and for the Multissol and Altis 99 cultivars at an N dose of 120 kg ha-1 were used for the 2016 harvest. In 2017, the BRS 122 and Multissol cultivars received N doses of 88.6 and 99.1 kg ha-1, respectively, and the Altis 99 and Aguará 06 cultivars received N doses of 120 kg ha-1. The use of fertigation allowed greater efficiency for the N doses in the sunflower cultivars in the semiarid region.