The economic importance of rice and the specifics of its use in production

Economic importance of rice and geography of its production

Rice is one of the most important cereal crops in the world, cultivated in more than 60 countries to provide food for more than half of humanity. In terms of sowing area and gross grain harvest, the crop ranks second in the world after wheat. Rice grain is characterized by high taste qualities, easy digestibility, and dietary properties, and rice decoction possesses healing properties. Rice protein contains an increased amount of the second group 191 of essential amino acids, such as lysine, valine, and methionine.

The crop is widely used not only in the food industry but also in livestock and technical sectors. Flour is obtained from rice grain, which is unsuitable for bread baking, as well as phytin, vitamin E, and other medical preparations. Rice germs serve as raw material for the production of oil used in soap making and candle manufacturing. Rice starch is of high value for the textile, perfume, and medical industries.

• Average global yield — 19 centners/ha
• Nutritional value of rice straw — 0.24 feed units/kg
• Crude protein in straw — 22 g/kg

Rice bran and straw are used for feed purposes. In terms of its feed value, rice straw surpasses wheat straw. In addition, straw is used for the manufacture of paper, thin cigarette paper, cardboard, ropes, bags, mats, and other household goods. In China and Japan, alcoholic beverages are traditionally produced from rice — rice wine and vodka (sake).

China and India produce the main world volumes of grain. In Russia, rice is cultivated under irrigation in dry-steppe regions in the Kuban, the Far East, and in the lower reaches of the Volga and Don. The climatic conditions of some neighboring regions impose restrictions on the introduction of the crop.

Botanical diversity, origin, and processing of the crop

The rice genus includes about 20 species growing mainly in the tropics and subtropics of Asia, Africa, America, and Australia. Cultivated rice (Oryza sativa L.) is divided into three main subspecies, which differ in the shape of the caryopsis. In Russia, the Chinese-Japanese subspecies of rice is the most common.

In Africa, the local population grows African, or glabrous, rice (Oryza glaberrima Steud.). In addition, grain of wild species is traditionally collected for food. These include the following varieties:

• spotted rice (Oryza punctata Kotschy ex Steud.);
• short-ligule rice (Oryza barthii A. Chev.).

By type of technological processing, rice is divided into brown, white, and parboiled. Minimal processing of brown rice preserves most of the nutrients of the grain. White polished rice undergoes the deepest cleaning, and steaming allows vitamins and minerals to be retained inside the kernel. Red rice possesses special properties — a traditional Thai variety, which has recently begun to be cultivated in the south of France.

1. Soak round unhulled red grains overnight to reduce subsequent cooking time.
2. Boil the prepared rice for 25 minutes (without preliminary soaking, the grain cooks for about 45 minutes).

In India, rice is called "arikhi," in Persia — "aryz," and the scientific name "oryza" is taken from the Greek language, into which it passed from Persian. India and China are considered the historical homeland of the culture, where it was cultivated as early as 3–4 thousand years BC. In the territory of Transcaucasia and Central Asia, rice began to be grown in the II–III centuries BC; it came to Europe in the VIII century, and penetrated into Russia through Hungary and Ukraine in the XV century under the name "Saracen wheat."

Commercial types of rice grain and their properties

The properties of commercial rice grain directly depend on the method of its post-harvest processing and cultivar characteristics. For the producer, this determines not only the market niche but also the storage technology. For example, brown rice retains the bran shell, thanks to which it surpasses white rice in nutrient content, however, its storage life is limited due to the presence of oil in the shell. Below are the main commercial types of rice and their characteristics, which processors are guided by.

Agrobiological requirements and stages of crop development

Rice is a self-pollinating, annual, heat-loving, short-day spring crop. Its root system counts up to 300 roots with a small number of root hairs, which are concentrated in the top 25 cm layer of soil. The stem is a hollow straw 80–120 cm high with leaves up to 35 cm long and 2 cm wide, ending in an apical panicle. The crop shows the best productivity on chernozems and floodplain soils.

• Sum of effective temperatures — 2200–3200 °C
• Duration of the growing season — 90–140 days
• Optimal growth temperature — 25–30 °C
• Maximum cultivation temperature — 40 °C
• Depth of the main root mass — 25 cm

By nature, rice is a hygrophyte, which is why it is cultivated under constant irrigation or in regions with at least 1800 mm of precipitation per year. The anatomical structure of rice includes a developed system of intercellular spaces and air cavities, through which oxygen is transported to organs submerged in water. This allows the plant to function normally under conditions of paddy flooding.

The crop management technology is directly linked to the stages of organogenesis. Rice development goes through five main phases, each of which requires strict adherence to temperature and water regimes. Violation of these requirements at any stage leads to a loss of stand density or a decrease in panicle grain filling.

1. Emergence (5–15 days). The phase lasts from the appearance of seedlings to the formation of 1–3 leaves; during this time, the root system is actively growing. During this period, the crops should be without a layer of water. A decrease in temperature slows down development: frosts down to −0.5 °C are dangerous for seedlings, and at −1 °C, plants perish completely.
2. Tillering (25–30 days). Starts from the 3–4 leaf phase and continues until the formation of 8–9 leaves. The minimum temperature threshold for tillering is 12 °C; the optimal range is 23–26 °C. Application of nitrogen fertilizers at the height of this phase stimulates the development of large panicles on side shoots.
3. Stem elongation. The phase begins after the formation of 8–9 leaves. The main visual indicator is the appearance of the flag leaf, which is positioned perpendicular to the straw.
4. Heading. The inflorescence emerges from the leaf sheath of the top leaf. Flowering of the main panicle lasts from 5 to 7 days. Rice is capable of pollinating even with closed floral glumes.
5. Formation, filling, and ripening. This final stage of the growing season lasts 30–40 days, during which the final filling of the grain takes place.

Soil tillage, crop rotation, and nutrient management

• Depth of autumn ploughing — up to 27 cm
• Soil acidity (pH) — 5–6.5
• Soil temperature for sowing — 12–15 °C
• Sowing depth of seed — 1.5–2 cm
• Grain moisture for threshing — 15 %

Before sowing rice, the field is prepared from autumn. Autumn ploughing is carried out to a depth of up to 27 cm, leaving the soil for drying and aeration during winter. If there is high infestation with aquatic and coastal weeds, the ploughing depth is reduced to 12–14 cm and herbicides are applied. To destroy algae and weeds, the crops are sprayed with copper sulfate. Seed material before sowing is treated with Granosan seed treatment with a dye at a rate of 2 kg/t.

The best soils for rice are cohesive, heavy clay soils of river valleys that retain water well and are rich in organic matter. In crop rotation, the crop is returned to the same place after fallow for a maximum of 2 years, and after perennial legume grasses — for 3 years. A legume link of alfalfa, clover, or sweet clover clears the paddies of marsh weeds and enriches the soil with nitrogen. Fallow or green manure fallow is used for repairing paddies and combating red-grain rice forms by sowing winter rapeseed, peas, grass pea, vetch, soy, buckwheat, or cereal-legume mixtures.

Rice is very responsive to fertilizers, especially nitrogen-based ones. Organic fertilizers in the form of manure are applied during autumn ploughing in a fallow or reclamation field. Mineral nutrition is distributed according to the following scheme:

Nitrogen is applied in split doses: 20–30% before sowing or locally during sowing, 45–55% at the 3–5 leaf stage, and 25% at the booting stage. Potassium fertilizers are distributed equally: half during cultivation before sowing, and the second part as top dressing at the booting stage. Potassium, with a good nitrogen-phosphorus background, accelerates grain ripening, prevents lodging, and reduces plant susceptibility to Alternaria blight, Helminthosporium leaf spot, rice blast, and Fusarium wilt.

Sowing, Water Regime, and Harvesting

The optimal period for sowing rice lasts from April 25 to May 15. By this moment, water and the top layer of soil must warm up to 12–15 °C. Sowing is carried out using the drill method at a depth of 1.5–2 cm, followed by immediate flooding of the plots with a 5–7 cm water layer. Seeds germinate at 11–12 °C, but uniform emergence occurs at 14–15 °C, and plants develop most actively at a temperature of 25–30 °C.

At the beginning of the growing season, rice grows slowly, but due to developed air cavities in the tissues, it easily tolerates flooding with a layer of 10–15 cm. Its fibrous root system lies superficially, no deeper than 25 cm. A constant layer of water in the plots is maintained during most of the season. Flooding is stopped only during the time of seed germination and rooting, as well as at the end of the growing season — from the beginning of wax ripeness to full maturity.

Harvesting begins when 80–90% of grains in the panicle reach maturity and their husks turn a yellow-brown color. Due to the uneven ripening of panicles and the difficulty of threshing, rice is harvested using a two-phase method. This process consists of several consecutive stages.

1. Mowing rice into windrows at a height of 15–20 cm (if crops lodge, the stubble height is reduced to 5–8 cm).
2. Drying the mass in windrows for 3–5 days.
3. Threshing the windrows when grain humidity drops to 15%.