By the photosynthesis process, plants recycle carbon, replenish atmospheric oxygen, and together with animal life maintain the balance of atmospheric oxygen and carbon dioxide. In the interest of maintaining this balance, rather convincing arguments have been made which emphasize fuels that do not further modify our environment. Advocates urge that emphasis should be on utilization of recently produced plant materials instead of fossilized plant residues, thus assuring a short-term carbon recycle rather than the alternative return, to the atmosphere of carbon that has been stored for millions of years as coal and petroleum. Directly or indirectly, plant material is the source of all food, feed, and fiber throughout the world. Also, plants provide industrially important materials and chemicals in many forms. These solar collectors are the source of the world's most abundant renewable materials: cellulose, starch, lignin, and sugar. To a lesser extent, in general, plants also accumulate chemicals of a more highly reduced state and, pound for pound, in more highly energized forms as isoprenoids, waxes, esters, triglycerides, and other lipids.
In 1980, the Office of Technology Assessment estimated that bioenergy could supply, by the year 2000, from 4 to 17 quads of energy annually, or as much as 20% of the U.S. energy consumption. The exact amount contributed depends on various factors, including: availability of crop land, crop productivity, efficient conversion technologies, species energy content and net energy contribution, economics, societal needs, and public policy. Biomass contributed about 1.8 quads of U.S. energy in 1975, nearly 2.7 quads in 1981, and was predicted to contribute about 3.5 quads in 1985. Continued and expanded use of plant biomass for energy, fuels, raw materials, and chemicals now supplied by petroleum will require increased utilization of agriculturally derived materials that currently are wasted, as well as further identification and development of productive and desirable plants from among the 300,000 or so unused or underutilized species.
During the last decade, biomass advocates have suggested numerous plant species as sources of firewood, vegetable seed oil, fermentation substrates, and whole-plant hydrocarbons. However, the rationale for selecting one species over another is, with few exceptions, sketchy, ambiguous, or unavailable. James A. Duke in the "Handbook of Energy Crops" has brought together in one source information common to about 200 species most frequently proposed for energy production. The Handbook provides discussion and presentation of available information such as: nomenclature, uses, folk medicine, chemical composition, botanical description, germplasm, distribution, ecology, cultivation, harvesting, yields and economics, energy, biotic factors, and key references. The technologist, attempting to identify plant species that merit further attention or show promise for satisfying specific fuels, chemicals, and materials needs, should find this an invaluable reference source.
1Manager, Northern Agricultural Energy Center, Northern Regional Research Center, 1815 North University, Peoria, Illinois 61604.