Rice is one of the world’s most important food crops. More than half of the people in the world eat this grain as the main part of their meals. Nearly all the people who depend on rice for food live in Asia. In some Asian languages, the same word means eat and eat rice. Most rice is eaten as boiled, white grain.
Rice is a cereal grain. Like other cereal grains, including wheat, corn, and oats, rice belongs to the grass family. But unlike other grains, rice grows best in shallow water. Rice thrives in many tropical areas because of their warm, wet climate. Farmers usually flood rice fields to supply the growing plants with moisture. The flooding also kills weeds and other pests. China and India are the world’s leading rice-producing countries. Together, they produce more than half of the world’s yearly rice harvest. 
A type of grass called wild rice grows in central Canada and parts of the northern United States. In spite of its name, this grain is not closely related to rice.
The rice plant
Young rice plants have a bright green color. As the grain ripens, the plants turn golden-yellow. The grain becomes fully ripe from 90 to 150 days after planting.
Structure.
The main parts of a mature rice plant are the roots, stems, leaves, and head. A system of slender roots supports the plant’s hollow stems. Each stem may have as many as 12 to 14 nodes (joints). Long, narrow leaves grow from the nodes. The head grows from the top of the stem. The head is also known as the panicle. The panicle holds the kernels—that is, the seeds or grains—of the rice plant. Each panicle carries from 60 to 150 kernels.
A typical rice kernel measures from 1/4 to 3/8 inch (6 to 10 millimeters) long. The kernel has a hard covering called a hull. Underneath the hull are the bran layers, the endosperm, and the embryo. Several bran layers provide the outer coat of the kernel. They contain many of the kernel’s nutrients. The starchy endosperm makes up most of the kernel. It is the part of the kernel most often eaten. The tiny embryo is the part of the kernel from which a new plant grows. The embryo is also called the germ.
Growth and reproduction.
A new rice plant develops from the embryo inside the seed. The seed begins to sprout a few days after it is exposed to warmth and moisture. The first tiller (shoot) appears 5 to 10 days after planting. Some rice plants may send out as many as 30 tillers. Most plants, however, grow far fewer. More leaves appear as the tillers grow taller. The panicle grows from the top of the tiller. Some older varieties of rice grow from 48 to 72 inches (120 to 180 centimeters) tall. Most newer varieties stand from 31 to 39 inches (80 to 100 centimeters) high.
Rice plants begin to develop flowering parts 6 to 10 weeks after planting. The panicle forms inside the sheath. The sheath is a tubelike, leafy covering that surrounds the stem. After about 4 weeks, the panicle emerges from the sheath and bears flowers. Pollination must occur for grains of rice to develop. Rice can pollinate itself because each flower has both male and female reproductive parts (see Pollen). The flowers give rise to mature grains of rice 4 to 6 weeks after pollination.
Uses of rice
Food.
Nearly all the rice produced in the world provides food for people. Rice supplies about half the calories in the daily diet of many people in Asia. It is an excellent source of carbohydrates. Carbohydrates are nourishing substances that provide the body with energy. Although low in protein, rice becomes an important source of protein if eaten in large amounts. Rice also has small amounts of the B vitamins—niacin, riboflavin, and thiamine. In addition, it provides the minerals iron, phosphorus, potassium, and sodium. Rice has little fat and is easy to digest.
Most rice is eaten as milled white rice. Milled white rice has had both its hull and bran layers removed during milling. Brown rice has had its hull removed but not its bran layers. Brown rice is more nutritious than white rice because the bran layers contain most of the kernel’s vitamins and minerals. However, most people prefer white rice because it is less chewy than brown rice. It also takes about half as long to cook.
White rice may be treated in various ways to make it more nutritious. For example, much white rice is enriched with vitamins and minerals. Enrichment replaces the nutrients lost in removing the bran. In areas where rice is the main food, enrichment helps prevent beriberi, a disease caused by lack of thiamine (see Beriberi).
Rice may also be steamed under pressure with the hulls on before milling. This process, called parboiling, makes the kernels less likely to break during milling. In addition, parboiled rice keeps many of the vitamins and minerals usually lost during milling. The nutrients spread throughout the grain during parboiling. Quick-cooking rice is partially cooked after milling. The kernels become more absorbent in the process and need less time for final cooking.
Other uses.
Rice appears in many processed foods. Breakfast cereals, soup, baby food, snack foods, frozen foods, and flour may contain rice. Breweries use broken rice kernels to make mash, an important ingredient in beer (see Brewing (Mashing)). In Japan, rice kernels are used to make an alcoholic drink called sake, or rice wine.
Farmers may use rice hulls for fertilizer. They also add bran layers to livestock feed. In industry, hulls are sometimes used as an ingredient in such products as insulation, cement, and the liquid chemical furfural (see Furfural). A few producers extract cooking oil from the bran. Many people in Asia use the straw (dried stalks) from rice plants to thatch roofs. They also weave sandals, hats, and baskets from the straw.
Kinds of rice
Scientists have identified 20 species (kinds) of rice. But only two species are cultivated today—Asian rice and African rice. Nearly all cultivated rice is Asian rice. A small amount of African rice is grown, mostly in west Africa.
Asian rice can be divided into three main groups: Indica, Japonica, and Javanica. Indica rice is grown in India and other tropical regions. Japonica rice is cultivated in the cooler areas of Asia, including China, Japan, and Korea. It is also grown in Europe, North America, and Australia. Javanica rice is grown in Indonesia. Within these three groups, agricultural researchers have identified more than 70,000 varieties. Only a few hundred varieties are grown. 
For marketing purposes, growers classify rice into three types by the length of its grain. Short grain rice is less than 1/5 inch (5 millimeters) long. Medium grain rice ranges in length from 1/5 to 1/4 inch (5 to 6 millimeters). Long grain rice extends from 1/4 to 5/16 inch (6 to 8 millimeters). Long grain rice contains a large amount of amylose. Amylose is a starch that makes the rice dry and fluffy when cooked. Both short and medium grain rice have less amylose. As a result, they become moist and sticky when cooked. Most tropical varieties have long grains. Most varieties grown in milder climates have short or medium grains.
Rice also may be classified by how it is cultivated. Lowland rice, also called wet rice, is grown in flat fields that are flooded by irrigation. Banks of earth enclose the land into fields called paddies. Farmers cultivate lowland rice over about half of the world’s rice-growing land. This crop accounts for about 75 percent of total world production. Upland rice grows in areas too hilly for flooding. Such rice depends on rainfall for moisture. Growers cultivate upland rice over about a sixth of the world’s rice-producing area. Rainfed paddy rice is grown in the remaining rice-producing lands. Its cultivation combines features of lowland and upland cultivation. This rice thrives in paddies watered by rainfall rather than by irrigation.
Researchers produce hybrids by crossing (mating) different varieties of rice. Hybrids have improved yields. China grows most of the world’s hybrid rice.
Where rice is grown
Farmers grow rice in about 120 countries. In all, they plant about 410 million acres (165 million hectares) of rice each year. They harvest about 830 million tons (755 million metric tons). Rice grows best in areas with warm temperatures. Rice also needs plentiful moisture from rainfall or irrigation. Such favorable growing conditions occur mainly in many tropical regions and the valleys and deltas of certain rivers. These rivers include the Yangtze in China, the Ganges in India, and the Mekong in Vietnam.
Asian farmers grow about 90 percent of the world’s rice. China and India rank as the leading producers. Together, they grow about 50 percent of the world’s rice. Other top producers include Bangladesh, Indonesia, Myanmar, the Philippines, Thailand, and Vietnam. The chief rice-producing areas of the United States lie along the Mississippi River in Arkansas, Mississippi, and Missouri; the Sacramento River in California; and the Gulf of Mexico in Texas and Louisiana.
Nearly all rice is eaten in the country where it is grown. About 5 percent of the world’s rice crop is traded internationally. A few countries regularly import rice. Other nations import rice if their crop fails. The chief exporters of rice include India, Pakistan, Thailand, the United States, and Vietnam.
How rice is grown
Methods of growing rice vary, depending on the supply of labor and the level of mechanization (work done by machinery). In Southeast Asia and other developing regions, labor is plentiful. Much work is done by hand. Some farmers have oxen or water buffaloes for pulling plows. In the United States and other developed countries, farmers use machinery for most stages of production.
Most rice grows in areas of the world with a yearly rainfall of at least 40 inches (100 centimeters). But farmers can cultivate rice in drier regions by irrigating the land. Rice needs an average temperature of at least 70 °F (21 °C) throughout its growing season. It grows best in heavy, slightly acid soils that contain fine particles of clay. Such soils hold water well.
Growing rice involves four main steps: They are preparing the ground, planting, controlling diseases and pests, and harvesting.
Preparing the ground.
Rice grows best in a field covered with shallow water. Farmers build low dirt walls called dikes or levees to hold water in the paddies. Many Asian farmers flood their fields before leveling them. They work the soil into a soft mud to make it easier to plow and to bury weeds. The practice of working flooded land is called puddling.
In certain industrialized countries, rice growers level the ground with large earth movers. They make sure the land slopes slightly so it can drain quickly before the harvest. They use specialized machines to till (plow) the land and build dikes. Before planting, farmers may add mineral fertilizers to the soil to enrich it. The most commonly applied fertilizers are nitrogen, phosphorus, and potassium.
Planting.
In developing countries, farmers sometimes plant rice seeds directly in the ground. More commonly, however, they sow seeds thickly in small seedbeds. After several weeks, they transplant the seedlings to a flooded field. This method reduces the length of time rice occupies the main field by about 15 to 20 days. This is important in areas where several crops are grown on the same land each year. Transplanting seedlings also permits better weed control. Fewer weeds grow in the thickly sown seedbeds. In addition, farmers can remove weeds more easily in the main rice fields when the plants are larger.
Farmers transplant clumps of 3 to 6 seedlings into the muddy soil. The clumps are spaced 4 to 8 inches (10 to 20 centimeters) apart. They may be lined up in rows.
In industrialized nations, rice growers use a machine called a drill to place the seeds directly in the soil. If the soil’s moisture is low, they may flood the field briefly after planting. Then they drain the field so that the seeds can sprout and grow. The field may be flooded and drained a few more times before the plants reach a height of 3 to 6 inches (8 to 15 centimeters). A layer of water 2 to 8 inches (5 to 20 centimeters) deep is then left in the field until a few weeks before harvest. Rice growers in Australia and California scatter seeds onto a flooded field from small, low-flying airplanes. The seeds are allowed to sprout before they are sown to help speed their growth and to ensure that they sink in the water. Fertilizers also may be sprayed on the plants from an airplane.
Controlling diseases and pests
is an important part of growing a good rice crop. Fungi, bacteria, and viruses infect rice plants with diseases. Weeds compete with rice plants for nutrients in the soil. Such destructive insect pests as leaf hoppers and stem borers also attack rice. Farmers use chemicals to control many of these enemies. However, since many of these chemicals may be harmful to people and the environment, farmers must use care in applying them. Rice growers can best protect their crop from damage by planting varieties that can resist diseases and pests.
Harvesting.
Farmers drain the rice fields one to two weeks before harvest. The grain is ready for harvesting when moisture makes up 18 to 25 percent of its weight. The wet rice must be dried after harvesting, before storage and milling.
In less developed countries, farmers harvest the rice by hand. They usually cut the stalks with sickles or knives. Then they tie the stalks in bundles and dry them in the sun. The crop is then ready for threshing. Threshing is the process of separating the grain from the rest of the plant. The farmers may thresh the grain by beating the panicles against a slatted bamboo screen and letting the grain fall between the slats. Some farmers put the bundles of rice through a gasoline-powered thresher. In some areas, farm animals walk over the bundles to thresh the grain. If the grain needs further drying after threshing, it is spread out on mats in the sun.
In industrialized countries, large self-powered machines called combines harvest and thresh rice in one operation. The wet grain is then dried by heated air.
How rice is processed
Harvested rice, still in its hull, is called rough rice or paddy rice. Most rough rice is processed in mills and sold as milled white rice. Millers use machines for most of the work, even in less developed countries. There are three basic steps in processing harvested rice—cleaning and hulling, removing the bran layers, and grading.
Cleaning and hulling.
Cleaning removes dirt, straw, weeds, and other impurities from the rough rice. The cleaning equipment uses screens to sift out unwanted materials. Fans blow away lightweight debris.
After cleaning, the rice is placed in a machine called a sheller for hulling. In the sheller, the grains pass between rubber rollers or stone disks. The rollers or disks loosen the hulls without breaking the kernels. The hulls are separated from the grain by suction. A screen then separates the hulled grain from any remaining unhulled rice. Some hulled rice may be packaged as brown rice. But most of it is processed into white rice. Rice may be treated by parboiling or other methods to improve its food value.
Removing the bran layers.
After hulling, the brown rice passes through a series of machines that rub off its bran layers and embryo. The remaining endosperm becomes the white rice we eat. In some Asian countries, a single machine called a huller mill strips off both the hull and most of the bran. After milling, the kernels are packaged for sale. Most of the bran removed during milling is used in livestock feed.
Grading.
Millers sort the processed rice into different grades for marketing. In the United States, the Department of Agriculture sets standards for grading rice. It bases these grades on such qualities as the size and the moisture content of the kernels. The number of chalky or damaged kernels also affects the grade. These grades range from U.S. No. 1, for the highest quality rice, to U.S. No. 6, which is a lower quality rice. U.S. Sample is the lowest grade of rice.
History
No one knows exactly when or where rice originated. It probably first grew wild and was gathered and eaten by people in Southeast Asia thousands of years ago. Archaeologists have found evidence that people cultivated rice at least 10,000 years ago in southern China and Korea. Rice then spread northward in China and to Japan; westward to India; and southward to Indonesia. Cultivation of a separate species of rice began independently in West Africa’s Niger River Valley by about 1500 B.C.
Traders and explorers carried rice from Asia to other parts of the world. Rice cultivation had spread to Persia (now Iran) and Syria by 300 B.C. Europeans first learned of rice from Greek soldiers who accompanied Alexander the Great’s military expedition to India in the 320’s B.C. But rice was not cultivated in Europe until the Moors of northwestern Africa conquered Spain about A.D. 700. They brought rice with them. Rice was brought from Spain to Italy several hundred years later. Afterward, it spread to southeastern Europe. Spanish explorers introduced rice to the Caribbean region and South America on voyages during the 1400’s, 1500’s, and 1600’s.
Rice reached the American Colonies during the 1600’s. Colonists first grew it commercially in South Carolina about 1685. Rice soon thrived in the Carolinas and Georgia. After the American Civil War (1861-1865), rice production shifted westward. By 1900, farmers in Louisiana were growing about 70 percent of the rice in the United States. Rice became established as a crop in California in the early 1900’s.
In 1960, government agencies and private foundations set up the International Rice Research Institute in the Philippines. The institute worked to improve rice production as part of a worldwide effort to increase food production in developing countries. This successful effort was a part of what became known as the Green Revolution. In the 1960’s, researchers at the institute developed new varieties of rice that produce more grain than older varieties, especially when fertilized. Traditional rice plants often grow so tall that they fall over and destroy their panicles. The new high-yield varieties have shorter, sturdier stalks. As a result, they are less likely to topple. Since the 1960’s, scientists have worked to develop varieties that can better resist diseases and insects and can grow without irrigation.
In 2002, scientists finished determining the sequence (order) of all the genes (units of heredity) in rice cells. Biologists are using this information to determine ways to create varieties of rice that resist disease and provide better yields.
Today, farmers in developing countries use machines for plowing and other work once done by hand. In developed countries, computers help rice farmers plan production and control irrigation.
