Abstract
This study investigated the effects of two soil moisture levels (SM) (30% and 70% soil available water) and three harvests (90 days, 118 days, and 151 days after seeding) on sweet (S506) and fiber (B133) sorghum genotypes under rain-sheltered conditions. Juice and bagasse-derived ethanol and their sum (EtOHBJ, EtOHB, and EtOHJ+B, respectively) were assessed. Water use efficiency (WUE) was determined for sorghum dry weight (DW) and EtOHJ+B. S506 had similar DW, but higher sugar content than B133, resulting in higher EtOHJ (+32%) and EtOHJ+B (+9%). High SM-enhanced DW, juice and sugars content, determining a strong EtOHJ+B increase (+99% vs. low SM). Late harvest enhanced DW and EtOHJ+B (+107% vs. early harvest), despite decreasing extractives and increasing structural fiber components. Water use efficiency of EtOHJ+B improved with high vs. low SM, although differences faded in late harvest. Upscale of EtOHJ+B and WUE data indicated a range of 21,000–82,000 ha of sorghum cultivation and 60–117 Mm3 of irrigation water, as amounts of resources needed to supply an 85,000 m3·yr−1 bio-ethanol plant. This large variation in land and water needs depended on specific combinations between crop factors SM and harvests.
Highlights
Biofuels face a growing demand fostered by fossil fuels depletion, while providing mitigation of the climate change determined by fossil fuel combustion [1]
Water use efficiency of EtOHJ+B improved with high vs. low soil moisture levels (SM), differences faded in late harvest
In late vs. early harvest and high vs. low soil moisture, bagasse showed a decrease of extractives and concurrent increase in all fiber components, which are the premises for lower glucose yield in enzymatic hydrolysis
Summary
Biofuels face a growing demand fostered by fossil fuels depletion, while providing mitigation of the climate change determined by fossil fuel combustion [1]. Biomass sorghum (Sorghum bicolor (L.) Moench) featuring high, thick stems with small panicles, is much praised due to a low need of agricultural inputs, high resistance to drought, and high biomass production [3,4,5] This is supported by specific sources in the literature, indicating that biomass sorghum has a higher ratio of energy output to energy input compared to sugarcane, sugar beet, maize, and wheat [6,7]. Water is becoming a costly and much-debated resource in the management of bio-energy crops [10], which is accompanied by a growing fear that irrigating such crops would exacerbate the competition with food crops under limited water resources [11] It has become a crucial point of debate to assess water use efficiency (WUE), i.e., the amount of biomass or biomass-derived biofuels per unit water used for plant growth [12], as the premise for efficient energy production
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