Rice

Rice is the principle food source for one-half of the world's population.  Rice is unique among the cereals, as it is usually grown under flooded conditions for weed control.

	To understand the unique characteristics of rice that allows it to be flooded.
	To learn the climatic and edaphic requirements of rice and how this influences the distribution of rice.
	To understand the differences between rice production in small paddies and large fields, and the economic and social systems that cause this difference.
	To appreciate the role of the international rice research effort in improving world rice yield.
	To learn how rice is used and its value to human nutrition.

III. Overview

Rice is produced in the tropical and subtropical portions of all continents.  The world production of rice places it slightly behind wheat and ahead of corn in planted acreage.  The U. S. is the largest exporter of rice, not because of our production, but because other countries consume nearly all they produce to feed their populations.

Rice is unique among the cereals in being able to grow in flooded conditions.  The rice plant is able to transport oxygen to the submerged roots from the leaves where oxygen is released during photosynthesis.  Rice does best in temperate regions that have low summer rainfall with high light intensity.  Unlike corn, sorghum, and millet, rice is a C-3 cereal.  This means that increased light intensity has the potential to increase yield.

Rice is seeded in beds and transplanted in much of the world.  This means the rice seedlings are 30-40 days old before they are transplanted.  This practice has two purposes: In areas with growing seasons that are marginal for rice, transplanting allows for rice to be used.  In areas where the growing season is longer, by transplanting, two crops of rice can be planted back to back because of the growing season gained using the transplant.  The downside to transplanting rice is the labor involved.  This practice is usually found where labor is abundant and inexpensive, and the farms small.

In a developed country, rice is grown very differently.  Rice seeds are soaked to make them heavy and they are seeded from the air over prepared soil.  Water is added to the seedlings after they begin to grow and more water continues to follow the seedling until about 6 inches covers the ground.  Unlike the small paddy rice, harvested by hand, large combines with huge "rice tires" combine the rice after the water is drained.  This system is found where labor is expensive and machinery is available to replace labor.

IV. Economic Importance

1. Provides principal food source for about 1/2 of world's population.

2. It is produced in the tropical and subtropical portions of all continents.

3. Average world production - 303 million metric tons (slightly less than wheat, slightly ahead of corn).

4. Leading countries in world production:

• China
• India
• Indonesia
• Japan
• Thailand
• Burma

6. Leading states:

• Texas
• Arkansas
• Louisiana
• California

8. First commercial U. S. production, Charleston, SC (1685).

• Spread to North Carolina and Georgia
• After Civil War, production moved to Mississippi River country

Breeding

1. Rice yields in many Asiatic countries have been greatly improved by growing improved varieties developed by International Rice Institute (IRI) at Los Blanos, Philippines.

• Have short, stiff stems to stand high nitrogen, resist lodging
• Grow rapidly in the seedling state
• Tolerate low temperature in germination, seeding, and flowering stages
• Are resistant to alkaline and saline soils and to salt in irrigation water
• Resistant to disease and insects
• Mature uniformly and produce seed that has a period of dormancy so the grain will not germinate when harvest is delayed by rain
• Provide maximum field and milling yields
• Have desired cooking and processing qualities

1. Rice is unique among the cereals in being able to germinate and thrive in water.

2. The rice plant is able to transport oxygen to the submerged roots from the leaves, where oxygen is released during photosynthesis.

3. Grown most successfully in regions with mean temperature of 22⁰C (70⁰F) or above during entire growing season (4-6 months).

4. Rice yields are higher in warm, temperate regions that have low summer rainfall with high light intensity.

• This is because of disease and low soil fertility in much of humid tropics

6. Grown best in heavy textured soils, and an impervious subsoil (1-5 ft. From surface) best to hold flooding water.

7. Upland rice consists of certain varieties that can be grown without irrigation or submergence in areas of high rainfall where soils is wet most of the time.

• Yields are low
• Rarely grown in U. S.
• Important in some Asian, South American and African countries

1. Rice belongs to grass tribe oryzeae.

2. Has one flowered spikelet with two short glumes.

3. Is an annual.

4. Height is 2-6 ft. tall.

5. Tillers freely (4-5 per plant).

6. Can be propagated vegetatively for several years by transplanting rooted tillers.

7. Inflorence is a loose panicle (l flouet/spikelet).

8. Hull makes up 20% of grain.

9. Color of kernel:

• White
• Brown
• Amber
• Red
• Purple

11. Very large ligules and large auricles.

12. Normally self-pollinated.

13. Is a short day plant (varieties differ greatly).

14. Lowland rice varieties are most common.

• Short, medium, and long grain (5.5, 6.6, & 7-8 mm).

• Helps distribute harvest over longer time

17. Indica types are long grain rice's (tropical origin).

18. 10% of U. S. crop is short grain type (CA).

19. 50% of U. S. crop is long grain (southern states).

20. 40% of U. S. crop is medium grain type (CA and south).

Culture

1. Land should be plowed 10-15 cm (4-6 in.) In fall, winter, or spring depending on rotation sequence.

2. Seedbed preparation includes destruction of weeds.

• Firm, mellow seedbed
• Crops should be kept at a minimum

4. Land between levees is levied to a slope of no more than 1.5-2"/ft. to  permit drainage.

5. When seeding, avoid red rice.  It is serious pest in rice fields in U. S.

• Seeds shatter early and contaminate fields
• Spoils appearance of milled rice

7. In South, rice sown from April l to May 15.

8. In CA, April 15 to June 1.

• Seed sown too early may rot due to low temperature

10. Plant 1.2 inches deep.

11. Most of rice in California and much of rice in South is sown by airplane.

• This involves first flooding to depth of 4-6 inc.  This is for weed control.
• Seed soaked in burlap bags for 18-24 hor and drained 24-48 hr..
• 1/2 lb.. NaOCL (sodiumhypochlorite/100 gal. of soak water to check seeding disease, and deactivate germination inhibitors in hull.
• Soaked seed sinks down into soil, dry seeds would float and drift in wind
• Rice is able to germinate with a lower supply of O₂ than other cereals - get some O₂ from water

• Fields usually irrigated, drained, and drilled and flooded after crop is up

1. Rice requires from 24-60 acre inches of water.

• 2-20" of which is usually supplied by rainfall during the growing season.

3. In South, the soil usually contains sufficient moisture for seed germination as well as for seedling growth on drilled fields.

4. In California, drilled rice is irrigated after seeding and then irrigated and drained at intervals until about 30 days after seedlings emerge.

5. When plants are 6-8" tall, the land is submerged or flooded to a depth of 1-2".

• As plants grow taller, this depth is gradually increased until it reaches 4-6".

7. Final drainage occurs 10-15 days before the rice is fully mature.

• Fully headed, panicles turned down, ripening started

• Below 70⁰F, germination retarded
• Above 85⁰F, can cause poor root development

Fertilization

1. Dwarf types of rice respond well to 130 kg/ha of N in ammonium form.

2. Tall types will not do well with more than 35-90 kg/ha N.

• Ammonium sulfate most popular form
• Ammonium phosphate, anhydrous, urea, and Cyanamid are also used

4. In excessive amounts, N can cause rice to flower earlier.

5. Much of the N may be applied as a topdressing 30-70 da. after seeding.

6. In California, heavy N applications are beneficial unless rice follows a legume green manure.  Phosphorus and potassium are usually not required.

7. On some of the Gulf Coast soils, rice responds to 23-75 kg P₂O₅/ha and 23-25 kg/ha especially where large amounts of ammonium N are applied.

8. Some algae growing in the water fix atmospheric nitrogen.

Weed Control

1. Some of the major weeds which occur in rice fields include:

• Red rice
• Barnyard grass
• Tall indigo
• Mexican weed
• Redweed
• Spike rush

3. Seeding in water will suppress barnyard grass.

4. Crop rotation is effective.

5. Blue green algae controlled by adding copper sulfate to water.

Harvesting

1. Rice is usually harvested with self-propelled combines which are equipped with large rubber tires and mud lugs, or with crawler tractors.

2. It is dried promptly with heat.

3. Rice should be harvested when  the moisture content of the grain had dropped to between 18-29%.

• At this stage, kernels in the lower portion of the heads are in the hard dough stage while those in the upper portion are ripe

5. If short season varieties are sown early, a second rotation crop can be harvested in the same season.

• An application of N applied immediately after the first crop is harvested
• The yield will be lower than the original harvest

Rotations

1. When rice is grown continuously on the same land, yields become stabilized at low levels.

2. Weeds become more abundant after two or more rice crops.

3. In Gulf Coast region, rice is usually grown on the same land 2-3 years.  It is then seeded to pasture crops for 2-3 years.

• Pasture crops include grasses, clovers, and lespedeza
• In California, they include ladino, burclover and strawberry clover

5. In Arkansas, a water fallow is sometimes used.  They maintain 2-4 feet of water and grow
fish in it for two years.

• Excessive accumulation of ammonium Nitrate
• Recommend corn or sorghum to precede rice to utilize N

7. Rice lands in the Delta well suited to cotton, soybeans, corn, oats, lespedeza, and winter legumes.  Rice follows winter legume or lespedeza for green manure.

• Usually 2-5 year rotation

1. A large part of the rice crop is grown by transplanting.

• Results in two crops/year, better land utilization

3. The seed is sown in beds while the fields are still occupied by other crops.

4. When the seedlings are 30-50 days old, they are transplanted in fields (paddies) that have been stirred into a thin soup + mud into which clumps of 3-4 seedlings can be pushed easily.

5. There is no advantage to this method if the weeds are controlled to the same degree.

Milling

1. As rice leaves the thresher, the kernel is still enclosed by the hulls and is known as rough rice or paddy (45 lb/bu).

2. Rough rice is normally used as seed.  If damaged or of low quality, it is used for feed.  Otherwise, it is milled for human food.

3. When milled, rough rice yields about 64% whole and broken kernels, 13% bran, 20% hulls, and 3-4% polish.

4. The milling process:

• The rice is first fanned and screened to remove foreign materials
• It is conveyed to hulling stones where most of the hulls are detached
• The mixture is then aspirated to remove the detached hulls
• Hulls used for fuel or packaging
• The rice is padded on to paddy machines or separators which remove the rough rice from the hulled kernels.  The rough rice is returned to the hulling stones.
• The hulled kernels or "brown rice" is conveyed to hullers where the germ, along with part of the bran layer is removed by friction.
• The bran reel then separates the detached bran from rice.
• The rice is passed on to a brush for polishing where more of the bran as well as some of the starch cells are removed and screened out
• This power or rice "polish" is used as a feed
• A revolving cylinder steams the rice and it is finally coated with glucose and talc for appearance
• A 100 lb. bag is called a "pocket" of rice

• The procedure consists of soaking and steaming the rough rice until the endosperm starch is partly gelatinized.  Then the grain is dried and milled.
• The kernels are broken less in milling so the yield of milled rice is increased
• The rice keeps better due to partial sterilization
• More of the water soluble vitamins are preserved in the kernel.  The B+ vitamins in the bran and hulls are absorbed by the endosperm from the water used in soaking the rice

• Head rice - whole grains and nearly whole grains of milled rice
• Second heat - 1/2 and 3/4 kernels
• Screenings - 1/2 and 1/3 kernels
• Brewers rice - finely broken kernels used in breeding or distilling, as a starch additive or as feed
• Rice flower - sifted or ground, byproduct of milling used in food and in face powders
• 50% of the weight of rough long grain rice is head or second head; 60% for short grain rice

8. Those who subsist largely on well-milled rice sometimes develop beri-beri (deficiency of vitamin B₁).

• Occurs if rice not supplemented with meat, fish, soybeans, or vegetables

10. Much of the milled rice sold in the U. S. is enriched by the addition of vitamins and minerals before packaging.

 Diseases

1. Seedling blights:

• Caused by sclerotinium and other fungi
• Attacks young seedlings in warm weather
• Severe infection kills rice
• Rice sown early to avoid this
• Immediate submergence will check the disease
• Some fungicides also provide good protection

• One of most serious diseases in Louisiana, Texas, and Arizona
• Attacks seedlings, leaves, hulls, and kernels
• Resistant varieties may be only satisfactory control
• Seed treatment may protect against seeding blight

1. Rice stink bug.

• Sucks out contents of kernel during the milk stage leaving empty seed coat
• Control measures include early mowing of and winter burning of the coarse grasses in which the insect hibernates.

• Two are important
• Sugarcane borer
• Rice stalk borer
• The larvae tunnel inside the rice culms, eat the inner parts and cause panicles to turn white and produce no grain (called white head)
• They prefer large stems
• Over winter in rice stubble
• Borers killed by heavy grazing of stubble, mashing down or flooding stubble fields (done by holding water from winter rains).

V. Summary

Rice is critical to feeding the world's rapidly growing human population.  Rice is usually grown of heavy textured soils close to a water supply.  The largest portion of the world's rice is grown on small (l-2 ha) farms, utilizing hand labor to plant and harvest.  Significant improvement in rice yields have been produced at the International Rice Research Institute (IRRI) at Los Blanos in the Philippines.  This work has improved the ability of rice to respond to nitrogen, grow rapidly, germinate and flower at lower temperatures, and added resistance to both disease and insect pests and alkaline soils.  These characteristics have been made possible by breeding rice for these traits, and providing this improved rice to the millions of rice farmers in the world.  The success of IRRI has brought about the development of 18 more centers around the world working with other major crop species.

	What is the importance of rice as a world crop?
	How is rice different from other cereals, and how does this influence rice production?
	How is rice produced differently in developed and developing countries and why?
	What is the role of an international center like IRI?  How has this center contributed to world food supply?