Updated: Sep 8, 2020
The species Oryza sativa or Asian rice has undoubtedly been domesticated for more than 5,000 years in China. With the other species, Oryza glaberrima nicknamed “West African rice” or “Casamance rice”, they constitute today the staple food of the intertropical and tropical regions of all the Far East, South America, much of Africa and more than 50% of the world's population.
Where is Rice Planted?
It is possible to grow rice in a submerged pot or in a pond.
Rice is grown in regions with long hot seasons and high humidity, located between 46° north latitude (32° in Russia) and 35° south latitude, up to an altitude of 2,000 m below the equator. European rice is cultivated in the Mediterranean countries, in the Camargue marshes (France), in the Pô plain (Italy), in the Ebro delta and the Huerta in Spain.
There are several ways to grow rice: In a fresh, swampy or artificially submerged ground:
Dry cultivation (also called rain-fed rice growing because it takes advantage of the rainy season and sometimes of groundwater) uses a very large quantity of water 160 to 300 mm/ month during the growing season, which means between 1,000 to 1,800 mm for the entire crop, knowing that the water needs increase with the age of the plant.
Loamy or clay loam soils are the most efficient: 800-1000 mm/year is sufficient.
This cultivation method is often itinerant or is done using a systematic rotation on the plots to limit weeding.
Submerged culture, with varying degrees of water control, includes flooded (or aquatic) culture and irrigated culture. It requires 1,200 to 2,000 mm of water/year depending on the capacity of the soil to retain water.
Water saltiness should not exceed 1%. Submersion must continue until the grains mature, whilst avoiding heavy rains harmful to the heading and the harvest. Once the ear is mature, the water can be drained to facilitate harvesting.
Flowering requires a minimum temperature of 22 °C (optimum between 27 and 29 °C) combined with a humidity of 70 to 80%. The optimal maturation of the grain is obtained at 25 °C. The water temperature of the rice field must be between 13 and 40 °C with an optimum temperature in the range of from 30 to 34 °C.
The plot requires maximum sunshine of 14-15 hours per day and temperatures above 20 °C over a continuous period of 3 to 6 months.
The optimal average insolation for setting up rice cultivation is 500 calories/cm²/d; this factor directly influences the yield, especially in Indica varieties.
It is obvious that a soil with a low clay content does not allow an aquatic culture to be carried out, however a rich soil, with a fine texture containing at least 40% clay, sufficiently permeable and with a pH between 5 and 8 (optimum between 6 and 7) is well suited for dry crops.
How to Sow Rice?
Rice cultivation is first initiated in greenhouses in pots, in a way that saves time because germination requires a temperature of at least 14 °C (ideally between 30-35 °C).
Plots with a slight slope of 0.05% should be circumscribed so that they can be drained easily and with a maximum level difference of 20 cm, using earth bunds. Grass them to prevent them from collapsing.
A soil that is already fresh can accommodate a dry crop.
Work the soil by plowing to a depth of 15 cm or simply by aerating it with a broadfork. Bring the necessary manure based on soil conditions and the expected yield.
Soak the rice grains in clean water for a minimum of 12 hours (36 hours maximum).
Sow directly in rows spaced 20-30 cm at a rate of 10 g/m², or in pots 15 cm high, filled with soil.
Lightly cover the seedling, then pass the roller.
If you opt for aquatic culture, gently fill the trench with 5 cm of water; otherwise, keep the soil constantly moist with regular watering in the evening.
Germination usually takes one week.
Prick out the plants raised in pots when the size of the stems reaches 12-18 cm.
In aquatic culture, keep the water level at 5-10 cm. In dry cultivation, do not hesitate to follow with a roller in early culture when the temperature reaches 16-18 ° C to increase tillering. Fertilization happens at the time of tillering and at the start of the run.
Thin your seedlings on the row every 10 cm and weed as often as possible, manually or with approved herbicides (2-3 treatments/year). Crop rotation and tillage limit weed invasion.
Diseases, pests and parasites
Pyriculariasis disease remains the main scourge of tropical rice cultivation, causing leaf spots and sterility of the plant. Reducing the nitrogen content, avoiding periods of drought and sowing less sensitive varieties are the best means to fight it.
Helminthosporiosis, rhyncosporiosis, withering of the sheaths (Rhizoctonia), Sigatoka, various bacteriosis and virosis can have serious effects locally. The search for disease-resistant hybrids, in particular with the japonica group, remains the main means of control.
When and how to harvest?
Harvesting generally takes place after 3-4 months when the panicles lean, grains begin to turn yellow.
Dry the plot and wait another 2 weeks for the rice to turn completely yellow.
Harvest with a machine or manually cut the panicles using a sickle or scythe on a sunny day.
The panicles are dried in an oven at 80 ° C so that the humidity is 14% to prevent the grain from fermenting. Their color turns to dark brown. It is then time to beat the panicles to extract the grains known as "paddy rice" or raw rice. The grain remains buried between the envelopes that are the glumes and glumellae.
Paddy rice is less attacked during storage than milled rice.
“Cargo rice” or “whole rice” is obtained after the hulls are removed. The inner shell is preserved, while the pericarp is removed for white or refined rice of by abrasion then oiled with linseed oil or petroleum jelly before going into a talc and glucose preparation to become translucent. Brown or semi-complete rice is an intermediate rice between whole rice and milled rice.
Rice is most often eaten as whole grains, boiled or steamed. Gluten-poor rice flour is usually made into noodles.
Waxy or glutinous rice, poor in amylose, is used industrially as a thickening agent for sauces and puddings, rice cakes ...
In many areas of the delta, increasing the salinity of the water is a real scourge for rice growing. In the Camargue, a very shallow salt water table threatens the fertility of the environment. Cultivation is made possible by pumping water from the Rhône which dilutes the salt water of the delta. The heavy and hydromorphic soil (not sufficiently draining) makes its work difficult, not to mention the mistral and the sometimes excessive rains of the Mediterranean climate. This rice benefits from a Protected Geographical Indication since 1998. The varieties of the japonica group offer a panel of round, semi-long, long and very long rice, complete (red or brown), white, naturally flavored, unbeatable (after simple baking).
Properties and uses
Rice represents 20% of the world's food energy needs and the second tonnage harvested after corn. Rice is also used to make various derivative products such as alcohol, vinegar, starch, glucose, acetone, oil, pharmaceuticals, vitamin foods ... Brown rice and oil rice made from pressed rice bran offers important therapeutic uses. Cooked rice paste is also applied to skin conditions (boils, sores, blemishes, etc.) while the ingestion of sticky rice treats stomach aches and indigestion. Brown rice extracts have been used to treat breast and stomach cancer as well as warts, indigestion, diarrhea and nausea. Rice contains large amounts of melatonin, a hormone that is involved in the regulation of sleep in humans.
The husks of rice made up of lemons separated from the grain are used as fuel and the ashes of fertilizer. Straw, paddy, flour, broken rice are used as fodder, even if broken rice is often consumed by people in poor countries while fine grain is exported. The straw is also transformed into pulp.