Agriculture Reference
In-Depth Information
world and around 75 percent of the total grain production.
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Rain-fed lowland and upland
ecosystems are nonirrigated and produce less yield per hectare than irrigated rice. Flood-
prone ecosystems are areas subject to uncontrolled flooding that cover the fields with as
much as 4 m of water for months at a time. Varieties of rice adapted to this ecosystem are
able to elongate so that the leaves and grain float on the water surface.
Referring to Figure 3.23, it is easy to see that the largest rice-producing countries
are in Asia. Rice is a tropical crop, needing warm temperatures to grow and produce
grain. Depending on the specific variety, it takes from 90 to 200 days to produce a
crop. Rice does not tolerate freezing temperatures. It generally is grown in areas
with at least 1500 mm rainfall. Irrigated rice requires 7 to 9 million liters of water
per hectare.
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It is generally grown only in areas with a mean annual temperature
above 218C and high rainfall to supply the water needed by the crop.
3.4.2 Importance in Human Diets
Rice is the most important grain in Asian diets, providing 35 to 80 percent of the total
calories consumed. With reference to Figure 3.35, rice has the highest carbohydrate
content of the cereal grains but is the lowest in percent protein, fat, and fiber. Rice is
consumed as a milled grain. After the husk is removed, the brown grain is milled, or
polished, to remove the brownish bran layer from the seed. Typically, only 55 to 65
percent of the harvested weight is recovered as milled, white rice. A disadvantage of
milling is that minerals, vitamins, and fiber contents are reduced.
Most rice is eaten as a boiled dish. There are many variations on its preparation.
Depending on the type of rice, it may be boiled to form a sticky mass or steamed to
give a light, fluffy single-grain food. In many parts of Asia, rice is considered an essen-
tial part of every meal. Manufactured rice products include rice cakes, noodles, food
stabilizers, puddings, crackers, bread, puffed rice, popped rice, and alcoholic beverages.
3.4.3 Botanical Description
Rice is a member of the grass family. There are two cultivated species: Oryza sativa and
Oryza glaberrima. The most widely planted specie is O. sativa, with O. glaberrima
being commercially produced only in parts of Africa. Over thousands of years, two
strains of O. sativa have evolved; japonica and indica. Some scientists consider a
third class, javanica, as an intermediate strain between japonica and indica. Modern
rice varieties have been formed from crosses of many strains, and, in practice, it has
become difficult to easily identify a particular variety as belonging to a particular
strain. For example, NERICA or New Rice for Africa released by West Africa Rice
Development Association, C ˆte d'Ivoire, rice varieties are a cross between African
and Asian rice varieties having good production under upland, or dry, conditions.
Rice is classified as an annual grass, meaning the plant dies after forming seed. In
practice, some tropical rice-producing areas practice ratooning. This involves cutting
off the above-ground part of the mature plant, letting the field dry for a month, and
flooding the field again to permit new sprouts to grow from the base of the harvested
plants. Up to three harvests can be obtained from a single planting.
