Agriculture Reference
In-Depth Information
Wheat is grown in countries with one mild or temperate season. There is little pro-
duction in the humid tropics. In terms of total grain production, it is second only to
maize (Fig. 3.4). The leading country in terms of hectares planted is India, closely
followed by Russia, China, and the United States (Fig. 3.12). There is little production
in the humid countries of Africa, Indonesia, Colombia, and Venezuela. In India, wheat
is primarily a Kharif (winter) crop. Wheat is classified according to its grain character-
istics and planting season and is cultivated primarily for human consumption.
Barley is generally planted in those areas where climatic conditions do not permit a
good crop of wheat. This may be due to lower rainfall, shorter growing season, or less
fertile soils. There is little production in the humid tropics. The leading country in terms
of hectares planted is Russia, with 9,662,000 ha planted in 2005. Other countries with
significant areas planted to barley include Ukraine, Canada, Australia, Turkey, and
Spain (Fig. 3.13). There is little or no production in the humid countries of central
Africa, Indonesia, and the Philippines. Barley is classified both by grain type and by
planting season. It is planted primarily for animal feed and industrial use (brewing).
3.3.1 Climatic Adaptation
Wheat is cultivated in areas with 350- to 600-mm annual rainfall.
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Bread wheat types
are planted in areas with 450 mm or more rainfall, while other types are found in areas
with less rainfall. Wheat is also grown under irrigation where rainfall is irregular or
inadequate. Wheat is classified as either winter or spring type. Winter wheat is
planted in the fall and requires vernalization in order to complete its growth cycle.
After planting in the fall, winter wheat plants germinate and form a rosette of leaves
around the plant with the growing point remaining below ground level. Only after
exposure to a period of low temperatures (usually 32 to 508F) will the plants send up
a stem and flower to form seeds in early summer. Spring wheats do not have a verna-
lization requirement and so are planted in the spring to produce a crop for harvest in
summer. In both cases, wheat gives the best yields in relatively cool temperatures
during flowering. When planted in humid tropical conditions most wheat varieties
will produce poorly and are subject to damaging disease problems.
Barley can be grown in drier climates than wheat, often with only 200- to 350-mm
annual rainfall. Under very low rainfall conditions, barley yields may be as low as
500 kg/ha. Similar to wheat, barley types may be winter (sown in the fall) or spring
(sown in spring). Winter types require vernalization before they can complete their
life cycle to produce seed. Barley is widely adapted, being grown from inside the
Arctic Circle to tropical latitudes. Barley is also a cool-season crop. It does not grow
well in hot, humid conditions.
3.3.2 Importance in Human Diets
Wheat is a part of all western diets consumed as bread and many forms of pastries and
pastas. Wheat provides 20 percent of the food supply for all developing countries.
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In
the Middle East and North Africa area it comprises 44.3 percent of the total food
supply. Each pound of grain contains about 1500 calories.
