Energy of Sorghum Biomass Under Deficit Irrigation Strategies in the Mediterranean Area

The growing demand for renewable energy sources and the need to optimize water use in agriculture, particularly in water-scarce regions, highlights the importance of growing species suitable for semi-arid areas, such as sorghum (Sorghum bicolor L. Moench). Deficit irrigation strategies allow water savings by optimizing water use efficiency. However, the potential of sorghum for bioethanol production with deficit irrigation strategies is still not well studied. This work investigates the impact of three irrigation strategies (full, deficit, and regulated deficit) on the biomass yield, ethanol production, and water use efficiency of sorghum (‘KWS Bulldozer’) in a semi-arid Mediterranean area (the Apulia region, Southeastern Italy) over three growing seasons (2013, 2014, and 2017); irrigation needs were calculated from crop evapotranspiration using standard crop coefficients and soil water content measurements. Harvested biomass was analyzed for cellulose and hemicellulose content, and ethanol production was estimated using conversion models. The full irrigation treatment resulted in the highest biomass and ethanol production in all seasons (22,633 kg × ha−1, 28,367 kg × ha−1, and 23,835 kg × ha−1, in 2013, 2014, and 2017, respectively), highlighting the relationship between a full water supply and yield optimization. However, deficit irrigation showed a higher biomass and ethanol water productivity (10.93 kg × m−3 and 3.23 L × m−3, respectively) than other treatments, suggesting that moderate irrigation strategies can effectively balance production and sustainable water use. The results suggest the importance of adjusting irrigation practices to specific environmental conditions to improve the efficiency and productivity of sorghum.