Nitrogen Requirements for Ethanol Production from Sweet and Photoperiod Sensitive Sorghums in the Southern High Plains

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.Core Ideas Nitrogen recovery and use efficiencies of sweet sorghum juice and bagasse were measured for two years in Missouri. Nitrogen recovery efficiency was greatest in one study year when 224 kg N ha−1 was applied, with no differences in recovery in the second year. The N use efficiency of estimated total ethanol yield was greatest at 56 kg N ha−1.

Photoperiod sensitive (PS) sorghum, with high soluble sugar content, high mass yield and high drought tolerance in dryland environments, has great potential for bioethanol production. The effect of diluted sulfuric acid pretreatment on enzymatic hydrolysis was investigated. Hydrolysis efficiency increased from 78.9 to 94.4% as the acid concentration increased from 0.5 to 1.5%. However, the highest total glucose yield (80.3%) occurred at the 1.0% acid condition because of the significant cellulose degradation at the 1.5% concentration. Synchrotron wide-angle X-ray diffraction was used to study changes of the degree of crystallinity. With comparison of cellulosic crystallinity and adjusted cellulosic crystallinity, the crystalline cellulose decreased after low acidic concentration (0.5%) applied, but did not change significantly, as the acid concentration increased. Scanning electron microscopy was also employed to understand how the morphological structure of PS sorghum changed after pretreatment. Under current processing conditions, the total ethanol yield is 74.5% (about 0.2g ethanol from 1g PS sorghum). A detail mass balance was also provided.

Sweet sorghum ethanol yield component response to nitrogen fertilization

Conversion of cellulosic biomass such as agricultural residues to biofuels offers significant economic, environmental and strategic benefits. Photoperiod-sensitive (PS) sorghum is a tropical grass grown primarily in semiarid parts of the world, especially in areas too dry for corn. PS sorghum produces more than twice as much the dry mass per acre as corn, which makes PS sorghum biomass an excellent source of feedstock for cellulosic biofuel production, and PS Sorghum varieties with reduced lignin content have also been developed through mutation breeding, which is attractive for biofuel production. The objective of this research was to study the potential of PS sorghum for biofuel production. We studied the relationship among composition, microstructure, physical and chemical properties, conversion efficiency of PS sorghum, and the effects of acid concentration on sugar yields. Structure analysis technologies including scanning electron microscopy and X-ray, were used to understand structural changes during pretreatment and enzymatic hydrolysis.

Increasing demand for high-yielding biofuel feedstocks elicits the need for the alternative ethanol industry to fully understand sweet sorghum (Sorghum bicolor (L.) Moench) yield response to varying N fertilization rates in the Midwest U.S. has arisen. The objectives of this study were to determine the optimum N fertilization levels for the production of two sweet sorghum cultivars (Dale and Top 76-6) over three years in central Missouri. The effects of 5 rates of N fertilizer (0, 56, 112, 168, 224 kg-N ha) were tested on dry matter yields, stem juice yields, Brix, fermentable sugar yield, theoretical juice ethanol yield, theoretical lignocellulosic ethanol yield, and total theoretical ethanol yield. N rate was found to be significant across most years and yield parameter. Total dry matter yields averaged 16.8 Mg ha, juice yields averaged 9113 L ha, and fermentable sugar yields averaged 1055 kg ha across years and cultivars. Brix generally did not differ with N treatment and the cultivars performed similarly for most yield parameters. Total ethanol yields averaged 5828 L ha and were highest between 112 and 168 kg-N ha, indicating that producing sweet sorghum in Missouri may reach optimum yields within that fertilization range. Annual precipitation and temperature differences under dryland conditions greatly influenced dry matter, stem juice, and sugar yields, thereby affecting theoretical ethanol yields, such that years with decreased rainfall and lower temperatures coincided with decreased yields. Sweet sorghum is

A fundamental need for commercialization of sweet sorghum [Sorghum bicolor (L.) Moench] as a bioenergy crop is an adequate seed supply, which will require development of hybrid varieties using dwarf seed-parent lines. A set of six public sweet sorghum A-lines (Dwarf Kansas Sourless, KS9, N36, N38, N39, and N4692) were crossed with a set of six public sweet sorghum cultivars (Brawley, Kansas Collier, Dale, Sugar Drip, Waconia, and Wray). Grain, fiber, and sugar yields were determined, and conversion formulas were applied to estimate ethanol yields. Hybrids were grown in fields at Ithaca, NE, USA, in 1983–1984 fertilized with 112 kg ha−1 N. In terms of yield components and overall ethanol yields, one A-line, N38, was inferior. Average total ethanol yields from hybrids made on the other A-lines were not significantly different, suggesting that any of those five A-lines could be useful seed-parents. With the exception of grain yield, cultivars used as pollen parents were among the highest-performing entries for all traits. For all traits directly contributing to total ethanol yield (grain yield, juice yield, % soluble solids, sugar yield, fiber yield), hybrids were also among the highest-performing entries. Results of this study demonstrate that hybrid sweet sorghum with performance criteria equivalent to existing sweet sorghum cultivars can be produced on the sweet sorghum seed-parent lines A-Dwarf Kansas Sourless, A-KS9, A-N36, A-N39, and A-N4692. Identification of specific seed-parent × pollen parent lines with characteristics best suited for particular growing regions and end-user needs will be critical for commercial hybrid development.

BackgroundSorghum (Sorghum bicolor L. Moench) cultivars store non-structural carbohydrates predominantly as either starch in seeds (grain sorghums) or sugars in stems (sweet sorghums). Previous research determined that sucrose accumulation in sweet sorghum stems was not correlated with the activities of enzymes functioning in sucrose metabolism, and that an apoplasmic transport step may be involved in stem sucrose accumulation. However, the sucrose unloading pathway from stem phloem to storage parenchyma cells remains unelucidated. Sucrose transporters (SUTs) transport sucrose across membranes, and have been proposed to function in sucrose partitioning differences between sweet and grain sorghums. The purpose of this study was to characterize the key differences in carbohydrate accumulation between a sweet and a grain sorghum, to define the path sucrose may follow for accumulation in sorghum stems, and to determine the roles played by sorghum SUTs in stem sucrose accumulation.ResultsDye tracer studies to determine the sucrose transport route revealed that, for both the sweet sorghum cultivar Wray and grain sorghum cultivar Macia, the phloem in the stem veins was symplasmically isolated from surrounding cells, suggesting sucrose was apoplasmically unloaded. Once in the phloem apoplasm, a soluble tracer diffused from the vein to stem parenchyma cell walls, indicating the lignified mestome sheath encompassing the vein did not prevent apoplasmic flux outside of the vein. To characterize carbohydrate partitioning differences between Wray and Macia, we compared the growth, stem juice volume, solute contents, SbSUTs gene expression, and additional traits. Contrary to previous findings, we detected no significant differences in SbSUTs gene expression within stem tissues.ConclusionsPhloem sieve tubes within sweet and grain sorghum stems are symplasmically isolated from surrounding cells; hence, unloading from the phloem likely occurs apoplasmically, thereby defining the location of the previously postulated step for sucrose transport. Additionally, no changes in SbSUTs gene expression were detected in sweet vs. grain sorghum stems, suggesting alterations in SbSUT transcript levels do not account for the carbohydrate partitioning differences between cultivars. A model illustrating sucrose phloem unloading and movement to stem storage parenchyma, and highlighting roles for sucrose transport proteins in sorghum stems is discussed.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0572-8) contains supplementary material, which is available to authorized users.

The objective of this study was to assess the effect of preceding crops (soybeans, sunn hemp, upland rice, and sweet sorghum) on the succeeding sugarcane yield, total bioethanol production, and soil chemical properties within the sugarcane cropping system. Treatments with upland rice and sweet sorghum provided the greatest increase in soil available P, compared to uncultivated land (control) at the final sampling, preceding the sugarcane harvest. Treatments effects were not significantly different for soil organic matter. At sugarcane harvest, the upland rice treatment provided the highest cane yield compared to the unplanted land, yet was not significantly higher than the yield of the sweet sorghum treatment. The highest sugarcane ethanol yields were observed in the sweet sorghum–sugarcane and upland rice–sugarcane treatments. However, the total ethanol yield in both preceding and succeeding crops was found to be highest in the sweet sorghum treatment, followed by the upland rice treatment. Upland rice proved to be most suitable for farming systems which emphasized food security, whereas sweet sorghum was most desirable for farming systems which emphasized alternative biofuel production. Both crops improved the sustainable production of soil and sugarcane.

Sweet sorghum productivity for biofuels under increased soil salinity and reduced irrigation

Compared to grain sorghums, sweet sorghums typically have lower grain yield and thick, tall stalks which accumulate high levels of sugar (sucrose, fructose and glucose). Unlike commercial grain sorghum (S. bicolor ssp. bicolor) cultivars, which are usually F1 hybrids, commercial sweet sorghums were selected as wild accessions or have undergone limited plant breeding. Although all sweet sorghums are classified within S. bicolor ssp. bicolor, their genetic relationship with grain sorghums is yet to be investigated. Ninety-five genotypes, including 31 sweet sorghums and 64 grain sorghums, representing all five races within the subspecies bicolor, were screened with 277 polymorphic amplified fragment length polymorphism (AFLP) markers. Cluster analysis separated older sweet sorghum accessions (collected in mid 1800s) from those developed and released during the early to mid 1900s. These groups were emphasised in a principle component analysis of the results such that sweet sorghum lines were largely distinguished from the others, particularly by a group of markers located on sorghum chromosomes SBI-08 and SBI-10. Other studies have shown that QTL and ESTs for sugar-related traits, as well as for height and anthesis, map to SBI-10. Although the clusters obtained did not group clearly on the basis of racial classification, the sweet sorghum lines often cluster with grain sorghums of similar racial origin thus suggesting that sweet sorghum is of polyphyletic origin within S. bicolor ssp. bicolor

Study on genotypic variation for ethanol production from sweet sorghum juice

The non-food dimension in the EEC research programmes

Sweet sorghum [Sorghum bicolor (L.) Moench] is a potential feedstock for ethanol production in many regions of the world. The objective of this study was to compare sweet sorghum cultivars with maize (Zea mays L.) as alternatives for ethanol production in the northern Corn Belt. Thirteen sweet sorghum cultivars were compared with an adapted maize hybrid grown on clay loam soils (Aquic or Typic Ha‐pludols) in a randomized complete block design in 1987 and 1988. The fermentable carbohydrate content, or Brix (°B), of sorghum stalk sap was measured with a refractometer, and ethanol yields were calculated assuming 14.7 pounds fermentable carbohydrate per gallon ethanol. Ethanol yield from maize was calculated from the harvested grain assuming 22.4 lb maize grain per gallon of ethanol. Sorghum cultivars varied significantly in dry matter production, °B, fermentable carbohydrate yield, and ethanol yield. The best sorghum cultivars (Keller, Dale, and Smith) produced more ethanol than maize in 1988, a dry year, and were similar to maize in 1987, a more normal year. Averaged over both years, public cultivars Keller, Dale, and Smith were superior to most other sorghum cultivars or hybrids. Lodging was most severe for the sweet sorghum cultivars with the highest fermentable carbohydrate yields. Sweet sorghum appears to be a viable alternative source of ethanol compared with maize for the northern Midwest, but high fermentable carbohydrate, lodging resistant cultivars are needed.

Sorghum (Sorghum bicolor L. Moench), including sweet sorghum, is widely adapted to diverse and often marginal crop production environments. Sweet sorghum stalks have high sugar content compared with other sorghum types and has potential for producing ethanol to be mixed with gasoline or for producing ethyl tert-butyl ether, an octane additive to gasoline. Sweet sorghum was introduced to the United States for syrup production in the 1850s (Winberry, 1980). Production peaked following sugar shortages during World War II at about 136 million L yr-1 of syrup in 1946 (Hunter & Anderson, 1997), but thereafter declined because of low sugar prices and inadequate production efficiency. Sweet sorghum can be competitive with corn (Zea mays L.) and grain sorghum for ethanol yield when grain yield is less than 9 Mg ha-1, and is comparatively efficient in nitrogen use (Smith & Buxton, 1993). Sweet sorghum can easily substitute for corn or grain sorghum in many cropping systems. Currently, most ethanol produced in the U.S.A. is from the starch of corn grain with the support of federal subsidies. Energy gains with production of ethanol from grain are modest, typically ranging from 30 to 130% depending on N use efficiency, ethanol plant efficiency, and the efficient use of the distillers grain co-product. Sweet sorghum can be produced at less cost than corn, often with higher energy gains (Smith & Buxton, 1993). Rather than producing starch, sweet sorghum carbohydrates are stored in the stalk as sugar, with sugar concentrations of 8-20% (Rains et al., 1990). Conversion of sugar to ethanol requires less energy than starch as much energy is used to depolymerize the starch. Sweet sorghum has demonstrated potential to produce up to 6000 L ha-1 of ethanol in Iowa and Colorado U.S.A. (Smith & Buxton, 1993), equivalent to ethanol from approximately 20 Mg of corn grain. However, estimated ethanol yields were on average 33% more with grain of corn and grain sorghum compared with sugar of sweet sorghum for seven rainfed site-years in Nebraska U.S.A. (Wortmann et al, 2010). Seasonal availability, the need to transport and store much mass, and storability of sweet sorghum constrain sweet sorghum as a bio-energy crop. In planning for bio-fuel production, long-term sustainability of cropping systems must be considered. Sustainability of a cropping system is very much dependent on production environment and resource availability. In one study comparing the sustainability of different bioenergy crops, sweet sorghum, along with oil palm (Elaeis guineensis L.) and sugarcane (Saccharum spp.) for biofuel, were found to be more sustainable in comparison to

Sweet sorghum [Sorghum bicolor (L.) Moench] is a potential alternative feedstock for ethanol production, but its viability will depend upon knowledge of cultural practices which optimize energy yield. Several field studies were conducted in 1987 and 1988 to evaluate the influence of planting date, harvest date, N fertilizers, and plant density on performance of sweet sorghum for ethanol production in the northern Corn Belt. Four sweet sorghum cultivars were planted in late April, early May, mid-May, and late May of 1987 and 1988 at Waseca, MN. Percent fermentable carbohydrate (°Brix or °B) and stalk moisture content were measured at two week intervals from August through October and stalk dry matter and ethanol yields were determined at harvest In mid-October. Dry matter yields ranged from 8 to 10 tons/acre and ethanol yields from 326 to 423 gal/acre with the best cultivar, ‘Keller’. Dry matter yield decreased as planting date was delayed, but °B and stalk moisture were only slightly affected by delayed planting. Fermentable carbohydrate and ethanol yields were about 13% higher at earlier planting dates than at later planting dates. Keller, a late-maturing cultivar, had greater °B and ethanol yields than three other cultivars, but was nearly 100% lodged at harvest. Maximum stalk °B was produced mid- to late September. Neither N fertilizers nor seeding rate significantly affected fermentable carbohydrate or ethanol yield. Early planting dates and late-maturing cultivars with high °B levels are recommended for sweet sorghum, when grown for ethanol in the upper Midwest.