Relationship of potassium doses with bioethanol yield in sweet potato in Cerrado soil

Sweet potato-bioethanol yield was evaluated in response to potassium fertilizer application. Experiments were performed using a 5 × 2 factorial design in which factors included the amount of K2O applied to the soil, with five levels (0, 30, 60, 120, and 240 kg ha-1) and genotype, with two levels (industrial genotype BDGPI #25 and table genotype BDGPM #04). Root yield, root starch and soluble solid contents, bioethanol yield, and economic viability of potassium application for bioethanol production were evaluated. Potassium affected root yield of both genotypes, with the highest yield observed at 140 kg K2O ha-1. Root starch concentration at harvest depended on genotype potential rather than potassium dose. Soluble solid content in fresh roots was lower than that in cooked roots, in which case, maximum conversion efficiency was observed at 109,69 and at 123.75 kg K2O ha-1 for BDGPM#04 and BDGPI#25, respectively. Bioethanol yield reached 10,484 and 9,839 L ha-1 at 151.87 and 136 kg K2O ha-1 for BDGPI#25 and BDGPM#04, respectively. Genotype BDGPI#25 was more efficient than sugarcane in converting potassium to bioethanol at 151.87 kg K2O ha-1, producing 10,484.29 L of bioethanol. In turn, BGDPM#04 showed maximum conversion efficiency relative to sugarcane at 122 kg K2O ha-1.