As a main source of nourishment for over half the world's population, rice is by far one of the most important commercial food crops. Its annual yield worldwide is approximately 535 million tons. Fifty countries produce rice, with China and India supporting 50% of total production. Southeast Asian countries separately support an annual production rate of 9-23 million metric tons of which they export very little. Collectively, they are termed the Rice Bowl. Over 300 million acres of Asian land is used for growing rice. Rice production is so important to Asian cultures that oftentimes the word for rice in a particular Asian language also means food itself.
Rice is a member of the grass family (Gramineae). There are more that 10,000 species of grasses distributed among 600 genera. Grasses occur worldwide in a variety of habitats. They are dominant species in such ecosystems as prairies and steppes, and they are an important source of forage for herbivorous animals. Many grass species are also primary agricultural crops for humans. As well as rice, they include maize, wheat, sorghum, barley, oats, and sugar cane.
Typically, grass species are annual plants or are herbaceous perennials that die back to the ground at the end of the growing season and then regenerate the next season by shoots developing from underground root systems. Shoots generally are characterized by swollen nodes or bases. Leaves are long and narrow, varying in width from 0.28-0.79 in (7-20 mm). Flowers are small and are called florets. Grasses pollinate by using the wind to widely and opportunistically disperse grass pollen. The fruits are known as a caryopsis or grain, are one-seeded, and can contain a large concentration of starch.
Classified in the genus Oryza, there are two species of domesticated rice— O. sativa and 0. glaberrima. 0. sativa is the most common and often cultivated plant, occurring in Africa, America, Australia, China, New Guinea, and South Asia. The natural habitat of rice is tropical marshes, but it is now cultivated in a wide range of subtropical and tropical habitats. Unlike other agricultural crop grasses, rice plants thrive under extremely moist conditions and moderate temperatures. The ideal climate is roughly 75° F (24° C). Average plant height varies between 1.3-16.4 ft (0.4-5 m). Its growth cycle is between three to six months (agriculturally, this is broken down into three phases lasting approximately 120 days). Rice plants produce a variety of short- to long-grain rices, as well as aromatic grains.
There are three different types of rice: japonica, javanica, and indica. Japonica rice varieties are high yielding and tend to be resistant to disease. Javanica types of rice fall between japonica and indica varieties in terms of yield, use, and hardiness. Although quite hardy, indica yield less than japonica types and are most often grown in the tropics.
Because cultivation is so widespread, development of four distinct types of ecosystems has occurred. They are commonly referred to as irrigated, rainfed lowland, upland, and flood-prone agroecological zones. Irrigated ecosystems are the primary type found in East Asia. Irrigated ecosystems provide 75% of global rice production. Irrigated rice is grown in bunded (embanked), paddy fields. Rainfed lowland ecosystems only sustain one crop per growing season and fields are flooded as much as 19.7 in (50 cm) during part of the season. Rainfed low-land rice is grown in such areas as East India, Bangladesh, Indonesia, Philippines, and Thailand, and is 25% of total rice area used worldwide. Production is variable because of the lack of technology used in rice production. Rainfed lowland farmers are typically challenged by poor soil quality, drought/flood conditions, and erratic yields. Upland zones are found in Asia, Africa, and Latin America. It is the primary type of rice ecosystem in Latin America and West Africa. Upland rice fields are generally dry, unbunded, and directly seeded. Land utilized in upland rice production runs the gamut of descriptions. It can be low lying, drought-prone, rolling, or steep sloping. Usually, crops are either sown interspersed with another crop, intermittently with another crop, or the crop is shifted every few years to a new location. Lastly, flood-prone ecosystems are prevalent in South and Southeast Asia, and are characterized by periods of extreme flooding and drought. Yields are low and variable. Flooding occurs during the wet season from June to November, and rice varieties are chosen for their level of tolerance to submersion.
Rice is mostly eaten steamed or boiled, but it can also be dried and ground into a flour. Like most grains, rice can be used to make beer and liquors. Rice straw is used to make paper and can also be woven into mats, hats, and other products.
Since it has been such an important grain worldwide, the domestication and cultivation of rice is one of the most important events in history that has had the greatest impact on the most people. When and where the domestication of rice took place is not specifically known, but new archaeological evidence points to an area along the Yangtze River in central China and dates back as far as 11,000 years. Researched by a team of Japanese and Chinese archaeologists and presented at the 1996 International Symposium on Agriculture and Civilizations in Nara, Japan, radiocarbon testing of 125 samples of rice grains and husks, as well as of rice impressions in pottery, from sites located along a specific portion of the Yangtze unanimously indicate a median age of over 11,000 years. Another discovery of possibly the oldest settlement found in China, which is located closely upstream from the other sites, gives credence to the new findings.
In any event, it wasn't until the development of puddling and transplanting of the rice plant that the spread of rice as an agricultural crop really began. Practiced in the wetlands of China, the concept of the rice paddy was adopted by Southeast Asia in roughly 2000 B.C. Wetland cultivation techniques migrated to Indonesia around 1500 B.C. and then to Japan by 100 B.C. To the West, rice was also an early important crop in India and Sri Lanka, dating as far back as 2500 B.C. and 1000 B.C. respectively.
The spread to Europe, Africa, and America occurred more slowly, first with the Moor's invasion of Spain in 700 A.D. and then later to the New World during the age of exploration and colonialism. Rice has been grown in the United States since the seventeenth century in such areas as the southeastern and southern states, as well as California.
The only raw material needed for commercial production of rice is the rice seed or seedlings. Additional use of herbicides, pesticides, and fertilizer can increase the likelihood of a larger yield.
Varieties of rice are selected and grown specifically for their end use. In the United States, long-grain rice is typically used for boiling, quick-cook products, and soup. Whereas, shorter-grain rice is used in cereal, baby food, and beer/liquors.
1 Prior to planting, minimal soil manipulation is needed to prepare for
cultivation. If the rice will be grown on a hilly terrain, the area must
be leveled into terraces. Paddies are leveled and surrounded by dikes or
levees with the aide of earth-moving equipment.
- 2 Rice seeds are soaked prior to planting.
- 3 Depending on the level of mechanization and the size of the planting, seeding occurs in three ways. In many Asian countries that haven't mechanized their farming practices, seeds are sown by hand. After 30-50 days of growth, the seedlings are transplanted in bunches from nursery beds to flooded paddies. Seeds can also be sown using a machine called a drill that places the seed in the ground. Larger enterprises often found in the United States sow rice seed by airplane. Low-flying planes distribute seed onto already flooded fields. An average distribution is 90-100 lb per acre (101-111 kg per hectare), creating roughly 15-30 seedlings per square foot.
- 4 Once the plants have reached full growth (approximately three months after planting) and the grains begin to ripen—the tops begin to droop and the stem yellows—the water is drained from the fields. As the fields dry, the grains ripen further and harvesting is commenced.
5 Depending on the size of the operation and the amount of
mechanization, rice is either harvested by hand or machine. By hand,
rice stalks are cut by sharp knives or
- 6 If the rice has been harvested by hand or by a semi-automated process, threshing is completed by flailing the stalks by hand or by using a mechanized thresher.
- 7 Before milling, rice grains must be dried in order to decrease the moisture content to between 18-22%. This is done with artificially heated air or, more often, with the help of naturally occurring sunshine. Rice grains are left on racks in fields to dry out naturally. Once dried, the rice grain, now called rough rice, is ready for processing.
- 8 Hulling can be done by hand by rolling or grinding the rough rice between stones. However, more often it is processed at a mill with the help of automated processes. The rough rice is first cleaned by passing through a number of sieves that sift out the debris. Blown air removes top matter.
- 9 Once clean, the rice is hulled by a machine that mimics the action of the handheld stones. The shelling machine loosens the hulls from the rice by rolling them between two sheets of metal coated with abrasives. 80-90% of the kernel hulls are removed during this process.
- 10 From the shelling machine, the grains and hulls are conveyed to a stone reel that aspirates the waste hulls and moves the kernels to a machine that separates the hulled from the unhulled grains. By shaking the kernels, the paddy machine forces the heavier unhulled grains to one side of the machine, while the lighter weight rice falls to the other end. The unhulled grains are then siphoned to another batch of shelling machines to complete the hulling process. Hulled rice grains are known as brown rice.
Since it retains the outer bran layers of the rice grain, brown rice needs no other processing. However along with added vitamins and minerals, the bran layers also contain oil that makes brown rice spoil faster than milled white rice. That is one of the reasons why brown rice is milled further to create a more visually appealing white rice.
- 11 The brown rice runs through two huller machines that remove the outer bran layers from the grain. With the grains pressed against the inner wall of the huller and a spinning core, the bran layers are rubbed off. The core and inner wall move closer for the second hulling, ensuring removal of all bran layers.
- 12 The now light-colored grain is cooled and polished by a brush machine.
- 13 The smooth white rice is conveyed to a brewer's reel, where over a wire mesh screen broken kernels are sifted out. Oftentimes, the polished white rice is then coated with glucose to increase luster.
The milling process that produces white rice also removes much of the vitamins and minerals found primarily in the outer bran layers. Further processing is often done in order to restore the nutrients to the grain. Once complete, the rice is called converted rice.
- 14 White rice is converted in one of two ways. Prior to milling, the rice is steeped under pressure in order to transfer all the vitamins and minerals from the bran layers to the kernel itself. Once done, the rice is steamed, dried, and then milled. Rice that has already been milled can be submersed in a vitamin and mineral bath that coats the grains. Once soaked, they are dried and mixed with unconverted rice.
Quality control practices vary with the size and location of each farm. Large commercial rice farms in the United States more often than not apply the most effective combination of herbicides, fertilization, crop rotation, and newest farming equipment to optimize their yields. Smaller, less mechanized operations are more likely to be influenced by traditional cultural methods of farming rather than high technology. Certainly, there are benefits to both approaches and a union of the two is ideal. Rotating crops during consecutive years is a traditional practice that encourages large yield as is the planting of hardier seed varieties developed with the help of modern hybridization practices.
Straw from the harvested rice plants is used as bedding for livestock. Oil extracted from discarded rice bran is used in livestock feed. Hulls are used to produce mulch that will eventually be used to recondition the farm soil.
The essential use of irrigation, flooding, and draining techniques in rice farming also produces runoff of pesticides, herbicides, and fertilizers into natural water systems. The extensive use of water in rice farming also increases its level of methane emissions. Rice farming is responsible for 14% of total global methane emissions.
With one out of every three people on earth dependent on rice as a staple food in their diet and with 80-100 million new people to be fed annually, the importance of rice production to the worldwide human population is crucial. Scientists and farmers face the daunting task of increasing yield while minimizing rice farming's negative environmental effects. Organizations such as the International Rice Research Institute (IRRI) and the West African Rice Development Association (WARDA), and Centro Internacional de Agricultura Tropical (CIAT [International Center for Tropical Agriculture]) are conducting research that will eventually lead to more productive varieties of rice and rice hybrids, use of less water during the growing season, decrease in the use of fresh organic fertilizer that contributes to greenhouse effect, and crops more resistant to disease and pests.
Where To Learn More
Huke, R.E. and E.H. Rice: Then and Now. International Rice Institute, 1990.
Johnson, Sylvia A. Rice. Minneapolis, MN: Lerner Publications Co., 1985.
"Limiting Rice's Role in Global Warming." Science News (July 10, 1993): 30.
Normile, Dennis. "Yangtze Seen as Earliest Rice Site." Science (January 17, 1997): 309.
Riceweb. http://www.riceweb.org/ (June 29, 1999).
— Jacqueline L. Longe