Rice

Rice (Oryza sativa) is a staple food for nearly half of the world's population. Rice is a member of the grass family, which also includes wheat, corn, sorghum, barley, oats, and rye. Unlike other grains, rice is well adapted to aquatic environments. Rice originated in Southeast Asia, where archeological evidence—including carbon-dated grain imprints in pottery shards—indicates that it was under cultivation at least six thousand years ago. Cultivated rice consists of two subspecies, O. sativa subsp. indica, which is grown in the tropics and subtropics, and O. sativa subsp. japonica, which is grown in temperate regions.

Although rice is grown in 115 countries, over 90 percent of the crop is in Asia. In 1999 world rice area was 153 million hectares (Mha), and total production was 589 million metric tons (Mmt). India had the largest area, 43.0 million hectares, and China was second with 31.7 million hectares. However, yields in China averaged 6.33 metric tons per hectare (mt/ha) compared to 2.97 metric tons per hectare in India, so China had the largest total production. Other leading rice countries in 1999 were: Indonesia, 11.5 million hectares; Bangladesh, 10.5 million hectares; Thailand, 10.3 million hectares; Myanmar, 5.6 million hectares; Brazil, 3.7 million hectares; the Philippines, 3.9 million hectares; and Pakistan, 2.4 million hectares. The United States was far down the list at 1.4 million hectares, but with yields of 6.65 metric tons per hectare was well ahead of the world average yield of 3.84 metric tons per hectare.

Except for a small amount for seed, all rice is used for human consumption. Most rice is consumed in the country where it is grown, with about 5 percent going into international trade. In the late 1990s, five countries dominated export markets, in the following descending order: Thailand, Vietnam, the United States, India, and Pakistan. About 40 percent of the U.S. crop is exported, with leading destinations being Latin America, Europe, Africa, and the Middle East.

Cultivation Techniques

Rice is grown under conditions ranging from full flood to rainfed upland conditions. Highest yields are obtained under flood, so the half of the world's rice area that is flooded produces 75 percent of the total crop. U.S. production is all flooded. Although rice is primarily a tropical or subtropical crop, it is grown from 53°N to 40°S. Interestingly, highest yields are obtained in high-latitude temperate areas such as Australia, Egypt, Korea, Italy, Spain, Uruguay, and the United States. High yields in the temperate areas occur because of longer day length, fewer storms, and relative freedom from the traditional diseases and insect pests of the tropics.

In the tropics and subtropics, rice is transplanted into flooded fields, following two or three weeks of initial growth in seedbeds. Most transplanting is by hand, but machine transplanting is becoming popular as labor costs increase. In temperate regions rice is direct seeded, either with grain drills into soil or water seeded by airplane into flooded fields. In all cultivation systems, highest yields are obtained by keeping the floodwater on for as much of the season as possible. Fertilizers are applied before and during the growing season, and weeds are controlled by handweeding and herbicides. About two or three weeks before harvest, fields are drained. In the tropics and subtropics, harvest is by hand while in temperate regions grain combines are used. All harvesting techniques involve threshing the grains from the panicles at the top of the plant. Man-hours per hectare for producing rice are as high as 300 in hand-transplanting cultivation, but are as little as 20 in mechanized cultivation in the United States. Total length of the growing season is 100 to 130 days. In the tropics two or even three rice crops may be produced per year, but in temperate areas only one crop is grown per year.

Harvest and Milling

At harvest, rice grain is called paddy or rough rice. In preparation for consumption, the hulls are removed by dehulling machines. Hulls, which are 18 percent by weight of paddy, have high silica content and are of little value except for onsite fuel or mixing into compost materials. Hull removal produces brown rice, which then is milled to remove the grain's outer layers, called bran, 10 percent by weight of paddy, and white rice, 72 percent by weight of paddy. Edible oil, about 2 percent by weight of paddy, is extracted from the bran and the remainder of the bran goes into pet food. Virtually all human consumption is as milled white rice, except for a small amount as brown rice in health food markets. In much of the world the milled rice goes into food use. In the United States, 81 percent of the domestic use of rice is for food, 15 percent for brewing, and the remaining 4 percent for seeding the next crop.

Worldwide, per-capita consumption of milled rice is 84 kilograms per year. Per-capita consumption is declining in developing nations as they become more affluent. In the United States, per-capita consumption is now 12 kilograms, which represents a doubling since the early 1980s. The increase in the United States is due to growth in ethnic groups who prefer rice, to recognition that rice is a healthful food, and to rice industry promotion efforts.

Rice and the Green Revolution

The Green Revolution began in the 1960s, when tall, lodging -susceptible rice and wheat varieties were converted to semidwarf varieties. The semidwarfs stand up better, produce more panicles per unit area, are more responsive to fertilization, and yield more. For example, in the pre-Green Revolution era of the early 1960s, world average rice yields were about 2 metric tons per hectare, compared to the 1999 average of 3.8 metric tons per hectare. The combination of high yielding semidwarfs plus more intensive cultural practices has driven the increase.

Wild Rice

In North America the term wild rice refers to an unrelated aquatic crop, Zizania palustris, which is grown in cooler areas such as Manitoba, Canada, and Minnesota. Small portions of Z. palustris grain are blended into gourmet preparations of regular rice. In Asia the term wild rice refers to the twenty related species of Oryza, which also are called weedy rice. One of these related species, Oryza glaberrima, is cultivated in Africa, but is being rapidly replaced by the higher-yielding O. sativa. The wild or weedy species of Oryza serve as sources of resistance to diseases and insects of cultivated rice.

J. Neil Rutger

Bibliography

Food and Agricultural Organization Statistical Databases. 1999. [Online] Available at http://apps.fao.org.

Riceweb. 1999. [Online] Available at http://www.riceweb.org.

Rutger, J. Neil, and D. Marlon Brandon. "California Rice Culture." Scientific American 244 2 (1981): 42-51.

Teubner, Christian, Eckart Witzigmann, and Tony Khoo. The Rice Bible. New York: Penguin Putnam, Inc., 1999.