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Biomass, Bioengineering of 147

lignocellulosic materials, i.e., they are composed mostly However, grasses contain a much wider variety of com-
of sugar polymers and lignin. ponents that do most tree species. In addition to cellulose,
hemicellulose and lignin, grasses often contain 10% or
more of protein, in addition to minerals, starch, simple
5. Forage and Grass Crops
sugars, vitamins and other components. The wider variety
For purposes of this article, we will not distinguish be- of components in grasses versus woody plants offers the
tween grasses and legumes, but will consider all non- potential for producing additional valuable products, but
woody annual and perennial plants as “grasses.” Most may also complicate the processing required.
grasses utilized by humans are employed for animal feed- To summarize this section, in very rough terms the
ing. Most forage grasses are also produced for local use world’s agricultural system produces about 2.5 billion tons
and are not widely traded, making it difficult to establish per year of total sugar, starch, oil, and plant protein to feed
a “market price” for many grasses. both humans and animals, as well as for some industrial
Available statistics on forage and grass crops are much uses. At least this much crop residue is also produced as a
less complete than for the sugar, starch and oilseed crops. byproductofsugar,starchandoilseedcrops.Cropresidues
However, there are approximately 7 billion acres world- are generally lignocellulosic materials. Additionally, well
wide devoted to animal pasture. If we assume that only over 10 billion tons per year of lignocellulosic materials
1 ton of forage grasses is produced per acre per year on are grown with some degree of human involvement as crop
such lands (the U.S. average for managed hay lands is and forest residues, animal forages and pasture, not in-
approximately 3 tons per acre per year), the total amount cluding the managed production of timber and pulpwood.
of animal forage from pasturelands is about 7 billion tons Many more billions of tons of lignocellulosic materials
per year, on a worldwide basis. In the United States we are produced annually in the biosphere with essentially no
produce at least 300 million tons per year of mixed forage human intervention. Thus the size of the lignocellulosic
grasses (dominated by alfalfa). resource dwarfs that of the food/feed resource represented
Forages and grasses vary widely in composition, al- by the sugar, grain and oilseed crops. Figure 3 attempts to
though they can be considered lignocellulosic materials. summarize these data on the annual production of biomass

FIGURE 3 World food and forage production (millions of tons).