Page 283 - Synthetic Fuels Handbook

FUELS FROM CROPS 269

equipment, either annually or semiannually for 10 years or more before replanting is needed
and that it is able to reach deep into the soil for water and use water very efficiently.
Switchgrass is a sod-forming, warm season grass, which combines good forage attri-
butes and soil conservation benefits typical of perennial grasses (Moser and Vogel, 1995).
Switchgrass was an important part of the native, highly productive North American tallgrass
prairie (Weaver, 1968; Risser et al., 1981). While the original tallgrass prairies have been
severely reduced by cultivation of prairie soils, remnant populations of switchgrass are still
widely distributed geographically within North America. Switchgrass tolerates diverse grow-
ing conditions, ranging from arid sites in the shortgrass prairie to brackish marshes and open
woods. The range of switchgrass extends from Quebec to Central America. Two major eco-
types of switchgrass occur, a thicker stemmed lowland type better adapted to warmer, moister
habitats of its southern range, and a finer stemmed upland type, more typical of mid to northern
areas (Vogel et al., 1985). The ecologic diversity of switchgrass can be attributed to three prin-
cipal characteristics, genetic diversity associated with its open pollinated reproductive mode, a
very deep, well-developed rooting system, and efficient physiologic metabolism. In the south-
ern range, switchgrass can grow to more than 3 m in height, but what is most distinctive is the
deep, vigorous root system, which may extend to depths of more than 3.5 m (Weaver, 1968).
It reproduces both by seeds and vegetatively and, with its perennial life form, a stand can last
indefinitely once established. Standing biomass in root systems may exceed that found aboveg-
round (Shiflet and Darby, 1985), giving perennial grasses such as switchgrass, an advantage in
water and nutrient aquisition even under stressful growing conditions.
Physiologically, switchgrass, like maize, is a C4 species, fixing carbon by multiple meta-
bolic pathways with a high water use efficiency (Moss et al., 1969; Koshi et al., 1982). In general
C4 plants such as grasses will produce 30 percent more food per unit of water than C3 species
such as trees and broadleaved crops and grasses and are well adapted to the more arid production
areas of the mid-western United States where growth is more limited by moisture supply.
Besides showing great promise as an energy crop for energy production, switchgrass
also restores vital organic nutrients to farmed-out soils and with its extensive network of
stems and roots (the plants extend nearly as far below ground as above), it is also a valuable
soil stabilization plant.

9.1.6 Reed Plants

Reed plants are a potentially prolific producer of biomass, capable of yielding 20 to 25 t/ha
of dry matter annually for a number of years. They can grow up to 6 m, are spread by means
of stout rhizomes and stolons, and are commonly found in swampy ground and shallow
water throughout temperate and subtropical areas.

9.1.7 Jerusalem Artichoke

The high-fructose syrups that can be derived from the tubers produced by the Jerusalem
artichoke may be used for the production of ethanol and other industrial raw materials.
Jerusalem artichokes also produce a large amount of top growth which may also prove to
be a useful source of biomass for energy purposes.

9.1.8 Sorghum
Sorghum is an annual tropical grass with large genetic variation that is a crop with the
potential for energy production. Sweet sorghum has been selected for its sugar content and