Rice

Rice

Scientific Name Oryza sp.
Common Names English: Rice; German: Reis, French: Riz; Spanish: Arroz

Occurrence

Agriculture Importance

Together with corn and wheat, rice is one of the most important cereal crops in the world. It is estimated that about 3 billion people depend on rice as a staple food, particularly in East Asia. Besides its nutritional value, rice is such an important crop for the following reasons: and it can be produced cheaply where labor costs are low; it grows comparatively quickly, including in regions with high precipitation that are thus unsuitable for other cereal crops. In the humid tropics and subtropics, about three quarters of the arable land is used for rice. In 2007, about 645 million tons of rice were produced, around 90 % of it in Asia. More than half of the harvested rice is consumed on the farms where it is grown.

Crop Management

for Rice:

Cultivation

A distinction should be made between 'wet rice' and 'dry rice' cultivation.
Dry or mountain rice is grown in a similar way to other cereals. It can only be produced in areas with sufficient and reliable precipitation (e.g. in parts of the Himalayas). Theoretically, the yield could approach that of 'wet rice', but in practice, it is limited by the supply of nutrients – and is therefore often significantly lower. 'Dry rice' production is labor-intensive due to the need for repeated weeding.
More than 80% of the rice produced worldwide is 'wet rice'. The rice field ('paddy' ) is flooded and the rice seeded or planted out into about 30 cm (11.81 inch) of water. The vegetation period depends greatly on variety and climate, ranging from three to six, sometimes nine months. Harvesting begins when the leaves turn yellow. 'Dead-ripe' rice (when seed and all straw parts of the plants can be easily broken with pressure) is less valuable.
In most countries, rice cultivation is still almost exclusively a manual exercise and the harvest, too, is done by hand, with sickles. In contrast, in the USA and Australia, sowing is often done by plane and the harvesting with combine-harvesters.

Cultivation Areas

In general, rice grows between latitudes 40° South and 50° North. Due to its temperature requirements (25 - 30°C; 77 - 86°F), 'wet rice' is rarely cultivated beyond the tropics or at heights above 1,200 m AMSL. 'Dry rice' needs an average temperature of only 18°C (64.4 °F) and can be found at altitudes of up to 2,000 m AMSL. The minimum temperature for the germination of sub-tropical rice varieties is 10°C (50 °F), whilst for tropical varieties, it is 18°C (64.4°F). Night frosts can be very damaging. Rice is able to grow with a comparatively low level of nutrients, but fertilisation will significantly increase plant vigour and yield. A natural source of nitrogen is supplied by the microscopically-small nitrogen-fixing blue algae, Nostoc spp. and - in symbiosis with the water fern Azolla spp. - Anabaena spp., which live between the rice plants in the water of rice paddies.

Special Information

Rice is one of the oldest cultivated plants in Asia. Some archeological findings of domesticated rice in China are dated at about 7000 BC. There is evidence, however, that early cultivation began independently in India, too.
It is estimated that the Oryza genus comprises up to 130,000 varieties and wild species.
Beginning in the 1960s, the development of high-yield varieties (HYV's) of rice has led to significantly increased production. Besides increased yield, an important aim in breeding is resistance to pathogens such as Pyricularia oryzae and Rhizoctonia solani. Genetic engineering is currently being used to improve the synthesis of vitamin A and iron storage (ferritin) in order to combat vitamin A deficiency and anaemia in developing countries.

Taxonomy

Family

Gramineae.
The genus name Oryza is probably derived from the Arabic word 'uruz' for rice; the genus belongs to the family of sweet grasses (Poaceae or Gramineae).
Some 74,700 varieties of Oryza sativa, the main cultivated 'Asian rice', have been developed around the world. They include, among others: O. sativa ssp. japonica (which has small panicles and produces awned round grains); O. sativa ssp. indica (which varies greatly in height and has smaller, thinner, awnless grains); and O. sativa ssp. indo-japonica or javanica (which is a cross between the two main varieties, and is often sterile).
The 'African rice' Oryza glaberrima features 1,300 varieties, and is also an important food crop, despite having been more and more displaced by O. sativa in recent years.

Use

Food

Rice not only has a high content of starch (72.7 g / 100 g): it also contains some valuable proteins, vitamins and minerals. It is mostly eaten together with legumes or vegetables. While most rice is grown as 'wet rice', 'dry rice' is often valued for its savoury flavour.

The grains have to be hulled in mills because of the high silica content of their husks. This produces wholegrain brown rice, which still has its seed coat, in which most of the vitamins are concentrated. Since brown rice requires longer cooking times and is often considered to be of inferior taste, the outer layers of the grain can be ground away to produce the so-called polished rice. This is, however, depleted of vitamins, as the rice grain is a caryopsis (i.e. the vitamin-rich seed coat is fused with the pericarp, so both are removed together). In order to reduce this loss of vitamins, brown rice can be 'parboiled', i.e. treated with hot steam under high pressure before polishing. This procedure results in about 80% of the water-soluble vitamins and minerals being relocated towards the inner part (endosperm) of the rice grains. Even so, the nutritional value of wholegrain rice is still superior to that of polished rice.

Broken rice grains originating from the milling process are used to make semolina, flour, rice starch and rice powder.
Rice oil, made from the bran, is valued for its antioxidant content and its high smoke point of over 250°C (482°F).

Beverage

Like other grains, rice can befermented to make alcoholic beverages such as 'Sake' ('rice wine') or – when molasses are added to the mash - 'Arrak'.

Industrial Products

Rice hulls and chaff are used as packaging, heating and insulating materials; rice oil is also used for the production of candles and soap. Traditionally, basketries, brooms and special 'rice paper' are made from the straw. Of course, all residues from processing that contain cellulose can be utilized for the industrial production of ordinary paper as well.

Facts on selected crops