Agriculture Reference
In-Depth Information
grown in a narrow north - south range. It can tolerate climates with as little as 500 mm
annual rainfall but yields best in areas with 1200 to 1500 mm rainfall.
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Sorghum is normally considered to be more “drought tolerant” than maize. The
root system of sorghum has more fine, secondary root hairs than maize, making it
especially efficient at extracting moisture in the soil. The physiology of the sorghum
plant also enables it to survive heat and water stress better than maize. Although it
can produce grain in very dry climates, most world production occurs in areas with
annual rainfall between 250 and 1250 mm.
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3.2.2 Importance of Grains in Human Diets
The usage of maize in human nutrition depends on both culture and physical factors. In
some parts of Latin America, other calorie sources are expensive. Animal protein is
expensive and difficult to preserve. As a result, almost 84 percent of the protein con-
sumed by lowest income groups in Mexico comes from maize. It is eaten fresh,
popped, as tortilla flour, cornbread, and as a thickening agent in soups. It is estimated
to provide about 70 percent of all caloric intake in rural areas of Mexico.
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Sorghum poses a special problem for human and animal nutrition. The seed of
many varieties has a high tannin content, giving it a bitter taste and making it difficult
to digest. There are varieties with very low tannin contents that are used in human diets.
In the countries where sorghum is widely planted, it is a staple food, being used boiled,
popped, fermented, in soups, and in various types of breads.
3.2.3 Botanical Description
Maize is a large member of the grass family, reaching heights of 2 to 5 m. It is a C4 type
plant, meaning it is especially efficient at converting sunlight to starch and proteins.
Plants bear both male and female flower parts, but they are separated. The male
flower is the tassel, developing at the top of the stem. The ear forms from the female
flower, which bears fine styles called silk. When pollinated, grain forms on the cob
to form an ear. The ear is covered by a husk made of specialized leaves, which
protect the grain from birds, insects, and fungi. The length of growing season varies
from 60 days to over 13 months (time from planting to dry grain).
Maize is classified according to its grain characteristics. Some of the major grain
types are shown in Figure 3.8. The major grain types recognized for trade are yellow
dent, yellow flint, white dent, white flint, floury, popcorn, and sweet corn. In terms
of nutrition, yellow and white grains have little difference. Dent and flint types
reflect the density of packing of starch grains in the grain. Floury-type maize has a
very loose starch grain packing and is easily damaged by insects. Popcorn has a
more vitreous endosperm than flint types. This holds in water vapor when heated to
cause an explosion when the kernel fractures (pops). Sweet corn is a mutant that
does not convert sugars to starch in the grain. The result is a grain with a sweet taste
when eaten in the immature stage. Many specialized types of maize have been devel-
oped to serve specific industry requirements. Examples include high-quality protein
