Potassium (K) participates in critical processes in sunflower cultivation, such as osmotic regulation and translocation of photosynthesis. However, the absorption or accumulation of this nutrient occurs differently owing to edaphoclimatic factors or between cultivars. The objective of this study was to evaluate the nutritional efficiency of sunflower cultivars as a function of different dosage K dosages in a semiarid region. To this end, two experiments were conducted in 2016 and 2017. The treatments consisted of five dosages of K at 0, 30, 60, 90, and 120 kg ha-1 K2O and four sunflower cultivars, Aguará 6, Altis 99, Multissol, and BRS 122. The experimental design was a randomized block with four replications and subdivided plots. The characteristics evaluated were agronomic efficiency, physiological efficiency, recovery efficiency, utilization efficiency, and accumulation of total K in the plant. Sunflower cultivars responded to K dosages in the two crops, with variations in efficiency parameters. Crop 2 showed better nutritional efficiency compared to crop 1. Aguará 6 showed greater nutritional efficiency than the other two crops. The use of dosages between 75 and 91 kg ha-1 of K2O provided better efficiency in K usage for the cultivars.