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Rice

Gramineae, Poaceae Oryza sativa L.

Source: Magness et al. 1971

Rice is the principal food crop in practically all the tropical realons of the world as well as in most subtropical areas and in some temperate zone areas having a relatively long growing season. Probably half of the world population depends on rice for its major food source. Rice is grown on around 200 million acres outside of Communist China - where data are not available. Probably an additional 100 million acres are grown there. World production outside of China has totaled more than 300 billion pounds in recent years.

In the United States rice acreage (1966-67) was just under two million - mainly in California, Arkansas, Louisiana and Texas. Production for the two years averaged 8 billion, 730 million pounds of rough rice, or approximately 4400 pounds per acre.

Rice has been cultivated since antiquity. Seeding of rice was a religious rite in China nearly 5000 years ago. The cultivated plant probably originated in Southeast Asia where wild types still persist. Rice cultivation in Europe began around 700 A,D. Rice was brought to America by the earliest colonists. All rice grown in the United States and most of that cultivated in other countries is of the species Oryza sativa L. This is really a cultivar species, not found in the wild. Some 20 to 25 species of Oryza are known, but the ancestry of the cultivated types is uncertain. The species O. glaberrinia Steud. is cultivated in Africa.

More than 8000 variety names for rice are knonvn, but many of these may be local names given to similar or identical varieties. However, many hundreds of varieties distinct in characteristics or in adaptation are known. These are roughly classed in three groups as follows:

Japonica Group: In general, varieties in this group have short kernels. Stems are stiff, short and upright. Leaves are short, dark green and the second leaf forms a narrow angle with the stem. Plants are pubescent and form many tillers. Panicles are numerous, short, dense and heavy. Spikelets are awnless. This group is generally grown in more northern climates as Japan, Korea, Northern China, Europe, and California in this country.

Indica Group: This group is more tropical in adaptation than japonica varieties and includes the kinds grown in Southern Asia, the Philippines, and the South-Central States in this country. These varieties are characterized by long kemels, long, light green leaves, tall, somewhat spreading stems, much less stiff than stems in japonica varieties. Panicles are numerous, long, light in weight, medium in density. Spikelets are awnless.

Bulu Group: This group is of minor importance compared with japonica and Indica. Varieties classed here are grown mainly on the islands off Southeast Asia. They are somewhat intermediate in characteristics. The kemels are large, stems are tall, stiff and upright. Panicles are few in number, of medium length and density, but heavy. Awns are numerous.

Rice Culture

The rice plant differs from most grains in that it thrives best when grown with the soil surface covered with water. Some rice is grown on soils that are not flooded; but soils well supplied with moisture are necessary and even then yields are much less than with flooded rice. This so-called "upland" rice is not grown in this country.

Rice seed requires a high soil moisture content to germinate. It germinates and grows readily when seeded on the soil surface under water. Much of the seeding in this country is on flooded sites, the seed being spread from airplanes. It may also be drilled in prepared soil, followed by flooding after growth starts. In Oriental countries where land is scarce, rice is often started in nurseries and transplanted to the field. This is economical of land use but does not result in higher yields than seeding in place.

For highest yields, fields are kept flooded from time of seeding or transplanting until shortly before harvest - with water 4 to 8 inches deep. Water should not become stagnant. If possible, a slow inflow and outtow of water should be maintained. An altemative practice is to draw off the old water and flood with fresh water at intervals.

In the United States nearly all rice is harvested with combines. Water is withdrawn 2 to 3 weeks before harvest so as to dry the soil enough for combine operation. Rice so harvested generally contains too much moisture to keep in storage and must be dried artificially prior to storage. An alternative method, no longer used in this country, is to mow the rice and let it lie in swaths to dry prior to threshing. Some modification of this method is widely used in most countries where rice is grown. In very humid climates the mowed rice may need to be removed from the field and kept off the ground to permit drying prior to threshing.

The Rice Plant: Rice is cultivated as an annual although plants will persist for more than one season, through rooting of tillers, in areas where freezing does not occur. Whether under water or in moist soil the central stem first emerges. Within a few days tiller or branch plants grow from buds in leaf axils near the soil level. The number of such tillers varies with the density of the plant stand and with the variety. Usually not more than half a dozen stems develop from a single seed , but up to 50 tillers may form on some kinds if very widely spaced. Only tilters that form early produce panicles and ripen grain.

Stem height ranges from less than 20 inches to 6 feet or more. Stems are hollow between nodes. Tall growing kinds are subject to lodging or falling over - particularly if fertilized. The shorter- and stiffer-stemmed varieties are therefore more satisfactory as use of fertilizers generally restilts in greatly increased yields. Recent development of short, stiff-stemmed varieties adapted to the tropics - coupled with the increased use of fertilizer possible on such varieties - is resulting in greatly increased production in South Asian Countries.

The panicle or seed bearing head roughly resembles that of oats but is more compact and tends to droop more. The panicle is usually 4 to 10 inches long with branches that rise singly or in whorls. Each branch bears several spikelets - each with a single flower. The panicles usually contain from 75 to 150 spikelets, but the number may be greater. The panicle is initially enclosed in a sheath. It emerces from the sheath about 75 to 80 days after seeding in the earliest varieties and in 125 to 130 days in late varieties. The period from panicle emergence to full seed ripeness is about 35 days.

The flower in rice consists of two small, sterile lemmas which partially cover the developing seed; floral bracts - the lemma and palea; and within these the stamens and pistil - or sex organs. As in most oat and barley varieties, the lemma and palea adhere to the developing seed or kernel. The lemma may be awned but is awnless - or near awnless in most cultivated varieties. The adhering lemma and palea constitute the "bull" of the threshed grain or so-called "rough" rice. After the hun is removed in milling the rice is tenned "brown" or "hulled." The hull comprises about 20 percent of the kernel weight. Further inilling removes the bran - or seed coat, the germ, and some of the endosperm. This results in about an additional 10 percent removal by weight.


Milling and Uses of Rice

The primary use of rice is for human food. For such use the hall, present on the threshed or "rough" rice, is first removed. In Oriental countries, for home use this may be done by use of a hollow block and wooden pounder - which leaves the bran layer and the germ on the rice. In the United States, other Occidental countries, and to a considerable extent in the Orient, rice is machine milled. This removes the hull, bran, germ, and some of the endosperm. The first step after cleaning the rice to remove any chaff and foreign matter, is to pass the kernels through a sheller which may consist of paired rubber rollers revolving at different speeds. Hulling stones may also be used. One horizontal stone is stationary and a second one revolves. When properly spaced they loosen the hulls with minimum kernel breakage. The product from this step is brown rice, the bran layer and germ being still present on the grain.

Brown rice is generally further milled in this and other Occidental countries to remove the bran and germ. This is accomplished by rubbing or scouring. A final step is termed brushing. It consists of passing the rice through a rapidly revolving vertical cylinder covered with overlapping pieces of cowhide or pigskin. This results in a polished surface on the grains.

A step termed parboiling, preliminary to hulling, is often used in Oriental countries and to some extent in this country. The rough rice is first soaked, then steamed either under pressure or without pressure, and subsequently dried before removing the hulls. This results in a toughening of the endosperm and less breakage. Also, minerals and vitamins present in the bran and embryo move into the grain proper to some extent, so parboiled rice is higher in these important nutrients than rice hulled without such treatment. In this country a process having a similar effect is sometimes used. The rough rice is first put under vacuum to remove air, then is soaked under pressure and finally steamed under pressure. This process shortens the time of treatment compared with parboiling and results in similar reduced breakage of the endosperm and enhanced nutritive value.

Milled rice is used mainly for direct consumption, usually after cooking by boiling. It may be sold as precooked or partially precooked rice. Rice is also used extensively as breakfast foods - as puffed rice, flakes, or rice crispies. Broken rice may be used as food or in manufacture of alcoholic beverages. Rice flour, a product of final milling, is used in various mixes. The bran is used mainly as livestock feed. Rice hulls are used for fuel, insulation, and in certain manufacturing processes.


Last update February 19, 1999 by ch