Effect of mineral fertilizer doses on sweet sorghum productivity and nutrient balance for bioethanol

The purpose of the study was to determine the mineral fertilizer dose that ensures maximum sweet sorghum biomass yield and bioethanol production in the eastern Forest-Steppe of Ukraine, as well as to establish the nutrient balance and the consistency of fertilizer doses with sustainable development principles. The research was conducted at the Ivanivka Research and Breeding Station (50°11ˈN, 35°03ˈE) from 2021 to 2023. The experimental design included five treatments: an unfertilized control and mineral fertilizer applications at rates of N60Р30K30, N90Р60K60, N120Р90K90, and the estimated rate N110P45K55. The study was carried out in four replications; each plot had a usable area of 100 m² and a harvested area of 73.1 m². It was established that the N120P90K90 and N110P45K55 fertilizer doses provided the highest biological productivity, with stem yields of 77.1 and 74.2 t ha-1, stem sugar content of 15.6%, and bioethanol outputs of 3.88 and 3.73 t ha-1, respectively. These fertilizer doses formed a positive soil phosphorus balance (9–49 kg ha-1), a slight nitrogen deficit (17–20 kg ha-1), and a pronounced potassium deficit (108–139 kg ha-1). In the long term, a potassium dose of 55–90 kg ha-1 may cause instability in potassium nutrition and require higher potassium fertilizer applications. Nitrogen doses of 110–120 kg ha-1 and phosphorus doses of 45 kg ha-1 were sufficient to achieve biomass yields above 70 t ha-1 and to meet sustainable development principles.