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Sweet sorghum seems to be one of the most promising energy crops for a wide range of ecological conditions thanks to its high yield potential and drought tolerance. A two-year field trial was conducted in a semi-arid Mediterranean environment in Turkey to evaluate the interactive effects of different nitrogen fertilizer levels (100, 150, and 200 kg ha−1) and humic substances (0, 15, 30, and 45 L ha−1) applications on the biomass and bioethanol yields of sweet sorghum, and combustion characteristics of its bagasse. Sweet sorghum showed a positive response to increased nitrogen fertilizer and humic subtances application levels in terms of biomass and bioethanol production. Lignocellulosic and total bioethanol yields significantly increased up to 2910 and 3336.6 L ha−1 as a result of the combined application of the 200 kg ha−1 N and 15 L ha−1 humic subtances (HS), respectively. However, HS application had a detrimental effect on the bagasse combustion quality, because it caused a considerable increase in the mineral and ash concentrations. Briefly, combined application of 200 kg ha−1 N and 15 L ha−1 HS may be suggested to be applied for the sustainable bioethanol production from sweet sorghum, while the application of HS likely does not provide any economic and environmental benefit if bagasse would be used as solid biofuel feedstock.