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Optimizing N fertilizer inputs is imperative for improving sweet sorghum [Sorghum bicolor (L.) Moench] yields and biofuel feedstock system efficiency. A 2-yr study was conducted to determine the physiological N-use efficiency (NUE) response in sweet sorghum's ethanol yield of stem juice, bagasse, and total ethanol yield (TEY). Two sweet sorghum cultivars ('Dale' and 'Top 76-6') were fertilized at five N fertilizer rates (0, 56, 112, 168, and 224 kg ha-1). At harvest, the stem juice and bagasse yields were measured then analyzed for the corresponding N concentrations and N contents. Whole-plant N recovery efficiency ranged from -1.5 to 57.6% across both years, with a significant N rate effect only in one study year. The NUE of juice ethanol yield only demonstrated an N response in the second year, whereas the NUE of lignocellulosic ethanol yield was greatest at the 56 kg ha-1 fertilizer rate each year. The NUE of total theoretical ethanol yield, determined as the sum of juice and bagasse conversion to ethanol, averaged 169 L EtOH kg-1 N across both years and was greatest at the 56 kg N ha-1 fertilizer rate in both years, and decreased at N rates exceeding 56 kg ha-1 in only one of the years. This study revealed that although sweet sorghum ethanol yields increased with N fertilizer application, NUE was greatest with low N fertilizer rates, consistent with previous research indicating that sweet sorghum is an appropriate biofuel feedstock for production in low-input systems or on marginal lands. [ABSTRACT FROM AUTHOR]

Emerging biofuel feedstock systems are well suited for use on less productive marginal soils in the Midwestern USA. The systems could replace commodity crop agriculture that may not be economically feasible on these soils with current input and output prices, and meet a growing renewable energy demand. Three annual bioenergy crops, maize ( Zea mays L.), sweet sorghum ( Sorghum bicolor (L.) Moench), and high biomass sorghum (HBS) were grown in rotation with soybean ( Glycine max L.) for five years on marginal soils at two locations. Maize aboveground dry matter (DM) yield and grain yield, sweet sorghum aboveground DM yield, and juice yield and Brix, and HBS DM yield were evaluated and used to calculate theoretical ethanol yields. Intermittent drought occurred at both sites during three of the five years notably reducing yield; a terminal drought in 2011 reduced sorghum yields and inhibited maize grain development at both sites. Theoretical ethanol yields averaged across years from sweet sorghum and HBS were greater than from maize at both locations, and indicate that sweet sorghum has the greatest yield potential, but HBS yield was the most stable. The central Missouri site maintained greater dry matter yield, and theoretical ethanol yield than the southwestern Missouri site. Due to the occurrence of drought during the study, the findings have relevance for evaluating marginal land management for annual bioenergy crops in differing rainfall patterns with climate change. [ABSTRACT FROM AUTHOR]

Perennial crops are considered as one of the most promising substitutions for fossil fuels for both ethanol production and direct combustion, but the quality and suitability of bioenergy feedstock is species dependent. The bioenergy feedstock value of different perennial crops is mainly determined by tissue composition and higher heating value (HHV). A common garden field experiment with four replications was conducted to investigate differences in cellulose, hemicellulose, lignin, ash, and 14 different tissue elemental concentrations as well as HHV from tissues of switchgrass (Panicum virgatum L.), Miscanthus (Miscanthus×giganteus), indiangrass (Sorghastrum nutans), eastern gamagrass (Tripsacum dactyloides), reed canary grass (Phalaris arundinacea), and giant reed (Arundo donax L.) grown in 2020 and 2021 in Midwest USA. Results showed that Miscanthus, switchgrass, and indiangrass exhibited higher holocellulose (cellulose + hemicellulose) concentrations compared with eastern gamagrass, reed canary grass as well as giant reed: 684–687 g kg-1 vs 597–646 g kg-1 (2-yr averages). Switchgrass and Miscanthus had higher lignin concentrations (97–108 g kg-1) than the other four species (66–84 g kg-1). Greater 2-yr averaged HHVs were observed in switchgrass (18.1 MJ kg-1) and Miscanthus (17.8 MJ kg-1) than for giant reed (17.3 MJ kg-1), eastern gamagrass (17.0 MJ kg-1), indiangrass (16.9 MJ kg-1), and reed canary grass (16.5 MJ kg-1), which was correlated with differences in ash concentration between switchgrass and Miscanthus (25–29 g kg-1) and the other four species (42–91 g kg-1). Switchgrass, Miscanthus, and indiangrass exhibited significantly lower nitrogen, sulfur, and potassium concentrations than the other grass species, which would lead to less NOx and SOx emission, and sintering or slag formation in the combustion chamber. Giant reed obtained the greatest potential ethanol and combustion yields on a single plant basis, followed by Miscanthus, switchgrass, indiangrass, eastern gamagrass, and reed canary grass; however, further studies are needed to evaluate biomass yields on an area basis. [Display omitted] • Lignocellulose was influenced by species and species × year effects. • Switchgrass and Miscanthus had higher heating values than the other species. • Higher heating value was negatively related with ash concentration across species. • Species differed in tissue ash and elemental concentrations. • SiO 2 was the largest component of ash, accounting for 32–68% across species. [ABSTRACT FROM AUTHOR]