Environmental Engineering Reference
In-Depth Information
difficult to convert into ethanol, thereby increasing the energy requirement for processing. The
bmr
mutant sorghum, pearl millet (
Pennisetum glaucum
), and corn lines have significantly lower levels
of lignin content (51% less in their stems and 25% less in their leaves). Purdue University research
showed 50% higher yield of the fermentable sugars from the stover of certain sorghum
bmr
lines
after enzymatic hydrolysis. Therefore, the use of
bmr
cultivars would reduce the cost of biomass-
based ethanol production. The
bmr
crop residues have higher rumen digestibility and palatability,
making them also good for fodder.
19.8.4 S
EEdling
c
old
t
olErancE
As a C
4
tropical crop species, most sorghum lines are susceptible to chilling stress during early-
season planting, and tolerance to early-season cold temperatures is a major trait that is needed in
many of the sorghum production areas of the United States. Stand establishment of sorghum is
adversely affected by air and soil temperature below 15ºC at germination, emergence, and early
seedling growth. Partial credit for a broader range of adaptation for maize can be given to breeding
efforts for improved seedling cold tolerance. Similar improvement in sorghum would allow for
expansion of this crop into cooler climatic regions. The University of Nebraska holds an extensive,
highly variable collection of over 500 lines of sweet sorghum. Cold-tolerant germplasm could serve
to expand the geographical range
of sorghum cultivation and minimize the inherent risks
involved
in early-season planting of sorghum within production areas. Additionally, an earlier sowing date
offers growers the option of capitalizing on higher levels of
available soil moisture and lower
evapotranspirative
demands in the early spring, potentially serving as a drought-avoidance
strategy.
Early planting of the crop within the Midwest would allow for multiple harvests. For example, in
Nebraska, cold-tolerant sweet sorghum has been planted on April 15, harvested in early August
(22 Mt/ha of dry biomass) and the ratoon crop harvested (12 MT ha
-1
) in mid October. The ratoon
crop alone equals a full season harvest of 1 ha of switchgrass. Improved seedling cold tolerance has
been attributed to seedling vigor and greater biomass (Cisse 1995).
19.8.5 S
ugar
y
iEld
Sweet sorghum is one of the many types of cultivated sorghum and is characterized by high
sugar content in the juice of the stem. Some lines attain juice yields of 78% of the total plant
biomass comprised of 15-23% soluble fermentable sugar. The sugar is composed mainly of
sucrose (70- 80%), fructose, and glucose. Most of the sugars are uniformly distributed in the
stalk, whereas approximately 2% are in the leaves and inflorescences (Vietor and Miller 1990).
The wide range of variability in soluble solids (brix; 15.5-24.9) and sucrose percentage (from
7.2 to 15.5%) indicates the high potential for genetic improvement to produce high sweet-stalk
yield coupled with high sucrose percentage sweet sorghum lines. In an early study, Ayyangar
et al. (1936) in crosses between gain and sweet sorghum suggested that a single dominant gene
controlled the nonsweet phenotypes. A more recent study (Li et al. 2004) suggested that more than
one gene with a dominant effect control the level of sugar in the stalks. Genotypic differences for
extractable juice, total sugar content, fermentation efficiency, and alcohol production have also
been reported. The predominant role of nonadditive gene action total soluble solids, millable
sweet-stalk yield, and extractable juice yield indicates the importance of breeding for heterosis
for improving these traits.
19.9 sorGhum JuIce harvest scenarIo
The options for harvesting sorghum include removing the whole or chopped stalk or pressing the
sugar-rich juice in the field and removing only the juice or the juice and pressed stalk. Chopped
stalks can be collected with traditional forage harvesters that are readily available and can be easily
