The optimal dose of cassava mill wastewater to be applied to the soil was calculated based on the potassium content found in the residue and the soil as well as the requirement of this nutrient by sunflower crops, and according to the reommendation proposed in Ribeiro et al. [14]. The remaining doses were calculated based on the optimal dose multiplied by factors two, four, eight, and sixteen of the initial dose. No mineral fertilization or liming was carried out during the experiment in order to evaluate only the effect of the cassava wastewater on the crop. Doses of cassava wastewater were applied to the soil once, and seeds were planted 15 days later to avoid the toxic effects of cyanide on seed germination.