Rice is an agricultural cereal crop, one of the most valuable in the world.
Source: commons.wikimedia.org©あおもりくま,(Aomorikuma) (CC BY-SA 4.0)
Economic importance
Rice is the second most sown area in the world after wheat and the third most harvested grain, after wheat and corn. In 1960-1981, the world’s sown area increased from 117.4 to 145 million hectares (21% of the grain sown area), about 90% of which are in Asian countries. The average rice yield in 1981 was 2.84 t/ha in the world, 1.74 t/ha in Africa, 2.9 t/ha in Asia, 4.76 t/ha in Europe, 1.75 t/ha in South America, and 5.5 t/ha in the USA. Over 60 countries are rice producers, primarily Asian countries: China, India, Vietnam, Indonesia, Korea, Japan, and the Philippines, but also Africa, America, and Europe (Italy, Spain, and Greece).
Rice grits are high in carbohydrates – up to 75.2%, low in protein – 7.7%, fat 0.4%, minerals 0.5%, fiber 2.2%, moisture – 14%. The yield of groats is 60-65%, the share of bran and germ of grain is 10-15%, husk and flakes 20-25%. Rice grits have good gustatory qualities and digestibility, and serve as a dietary product, including for children’s nutrition. Rice broth is used in folk medicine. Processing rice grits (cleaning and polishing) reduces their nutritional value.
Rice starch is used in the textile, perfume and medical industries. Rice germ is used to make rice oil for soap making and candle making. Rice straw is used to manufacture fine paper of the highest grades (e.g., for the manufacture of cigarettes) and cardboard, ropes, sacks, mats, baskets, etc.
The fodder value of rice straw is superior to wheat straw: 1 kg of straw contains 22 g of protein and corresponds to 0.24 fodder units. However, it is very coarse and more suitable for use as an organic fertilizer.
Rice is used for flour, starch, alcohol, beer, phytin, B vitamins.
History of crop
Rice is thought to be native to the tropical and subtropical belt of Southeast Asia. It is believed that cultivated rice originated from a wild form in Southern China.
In China, India, Japan and some other countries it began to be cultivated 4-5 thousand years ago. Rice was introduced into Spain and Egypt at the beginning of the 8th century.
In Europe, rice began to be cultivated in the Mediterranean countries (Italy, Spain, France, Greece, Croatia) and Bulgaria since the 15th century.
Cultivation areas and yields
In the former USSR, rice was cultivated mainly in Central Asia and Transcaucasia. During the Soviet period rice cultivation spread to the Far East, Kuban, Crimea, lower reaches of the Volga, Don, Dnieper, Bug, Danube and Kazakhstan. The northern border of this crop in Russia reaches 46° N, in the world – 42° N. – Hokkaido Island, Japan. In the mountainous areas, rice crops rise up to 2000 m above sea level.
From 1966 to 1980, rice acreage in the USSR grew from 100 to 585 thousand hectares, owing mainly to the construction of irrigation facilities.
The main rice growing region in Russia is Krasnodar Territory. In 1975 the gross output of rice here was 686.7 thousand tonnes or about 60% of the gross output of Russia (RSFSR) and about 34.5% of the USSR. The gross output of rice in 1971-1975 was 1.8 mln tonnes, in 1976-1980 – 2.3 mln tonnes. – In 1990 it was planned to reach the yield of 3.3-3.5 million tons.
In 1990s the area under rice cultivation in Russia was about 200 thousand hectares at the yield of 2.6 t/ha, while in 2001-2005 it was 150 thousand hectares or 0.3% of the area under cereals. Gross yield was 500 thousand hectares (0.6% of the grain yield), yield was 3.5 t/ha.
Rice is one of the most productive cereal crops. In 1971-1975, the average yield was 3.85 t/ha; in 1976-1980, it was 3.93 t/ha. – In 1976-1980, the average yield was 3.93 t/ha. The highest yield was in Krasnodar Territory: in 1975 it was 5.0 t/ha from the area of 137.4 thousand hectares of crops. At the Kuban experimental station for 20 years rice yield was on average 5.8 t/ha, at the “Kuban” educational and experimental farm of the Kuban Agricultural Institute – 7.81 t/ha. In 1982 the highest yields were obtained in the Crimea (rice farm “Pyatiozerny”) – 6.0 t/ha, in Krasnodar Territory (Sovetskaya Kuban state farm) – 5.46 t/ha from 1.5 thousand ha, and also in Khorezm Region (Uzbekistan, Al-Khorezmi state farm) – 7.0 t/ha from 3.5 thousand ha.
Kuban region remains the most promising rice-growing region due to richly filled soils of Kuban and Azov floodplains. The Far East (130-150 days, relatively cool), Northern Caucasus and Volga region (135-145 days, moderate) are the warmest regions (with more days per year with average daily temperature above +15 °C). These regions are also among the most promising for rice cultivation.
Botanical description
Cultivated rice (Oryza sativa L.) is an annual plant, subdivided into subspecies:
- Indian (indica), distinguished by its long and thin grains with a length-to-width ratio of 3-3.5:1;
- Chinese-Japanese (sino-japonica), has short and wide grains with a ratio of 1.4-2.9:1;
- Japanese (japonica).
In Russia, the most common are the Chinese-Japanese and Japanese subspecies. Each subspecies is subdivided into several varieties according to a number of features.
According to the modern classification, cultivated rice is subdivided according to grain length into:
- common (ssp. communis Gust.):
- Indian (indica), characterized by weakly pubescent flower scales, thin and narrow grains;
- Japanese (japonica), with densely pubescent floral scales, broad and thick grains:
- ordinary (v. utilissima L.) with vitreous grains;
- sticky (v. glutinosa Lour.) with a floury grain, which is digested into a sticky mass;
- short-grain, or fine-grain (ssp. brevis Gust).
Root system
Root system is fibrous, lies superficially, the main mass of roots is located at a depth of up to 25 cm, reaching 60-80 cm in depth. It has a well-developed air-bearing tissue – aerenchyma, which is also present in leaves and stems.
Owing to the aerenchyma, the necessary concentration of oxygen is maintained in rice plants. The number of roots per plant reaches 300, but they have relatively few root hairs.
Stem
The stem is a hollow straw 50-200 cm high (in domestic varieties 75-115 cm), strongly bushy, sometimes branching. The upper internodes are hollow, the lower ones are filled with heartwood.
The productive bushiness is 3-5 stems.
Leaves
Leaves are linear-lanceolate, narrow with ribbed veining, the edges are serrated, green, less often purple. They reach a length of 35 cm and a width of 1.5-2 cm. The uvula is shaped like an acute triangle, divided in half by a longitudinal crack.
Roots may form on the lower stem nodes under the water layer, taking part in plant nutrition.
Inflorescence
The inflorescence is a panicle, reaching a length of 20-30 cm, with a large number of branches. Spikelets are mono-floral, with 80 to 200 spikelets in a panicle. Flowers have 6 stamens and an oblong ovary. The outer raceme of the awned varieties has an awn.
Rice is a self-pollinating plant.
Fruit
The fruit is a filmy grain. At threshing, whole spikelets with flower and spikelet scales fall out. The endosperm is dense, horn-shaped. Grain weight per 1,000 grains is 25 to 40 g. 2-5% of the seed germ mass and 17-25% of the film mass come from the germ. Under unfavorable weather conditions, the film content may reach 35%.
Biological features
Morphological and physiological features of rice indicate its intermediate position between aquatic and terrestrial crops, so it is cultivated as a flooded or periodically irrigated crop. Without irrigation rice can be grown only in regions with strong moisture – more than 1000-1200 mm of atmospheric precipitation per year.
Temperature requirements
Rice is a very heat-loving crop. Seeds begin to germinate at 10-12°C, viable seedlings emerge at 14-16°C, and the optimum temperature for the emergence of seedlings is 22-25°C. The minimum temperature during tillering is 15-18°C, during panicle formation and flowering is 18-20°C, and at the beginning of grain ripening is 19-25°C. The optimum temperature for plant growth and development is 25-30 °C, and the maximum temperature is 40 °C (with sufficient flooding).
Lower temperatures slow down the growth and development of rice. At temperatures below 17-18 °C, plants under-ripening occurs. Frosts of -0.5°C are dangerous, and at -1°C are destructive; it does not tolerate abrupt changes in temperature well. The sum of effective temperatures during the growing season for different early maturing varieties varies from 2200°C (Santachezky 52) to 3200°C (Uzros 7).
Moisture requirements
Rice by its ecological nature belongs to hygrophytes. It withstands prolonged flooding with a water layer of 10-15 cm. Transpiration coefficient is 450 to 800, presence of permanent water layer reduces transpiration. Rice plants consume moisture most sparingly for creation of organic matter. The critical period for moisture is during tillering-formation of panicles. In the absence of irrigation, rice produces low yields even in wet areas.
When germinating, seeds absorb 25% of water of their own weight.
Root and leaf sucking power is low, and the suction surface of the roots is small because of the small number of root hairs. Abundant water supply is also associated with low and water content in plant tissues: 2 times less than in wheat.
The layer of water in the field contributes to:
- improvement of thermal and nutrient regimes;
- flushing out of saline soils;
- prevention of erosion;
- weed control;
- prolonged non-stop cultivation of rice;
- maintenance of optimal air humidity of 70-80%.
Light requirements
Rice is a short-day plant that requires 9-12 hours of sunlight. Early maturing varieties respond little to the length of daylight hours. Requires intensive insolation. Scattered light leads to incomplete ripening.
Soil requirements
The best soils for rice cultivation are sedimentary soils of river and riverine valleys, cohesive, heavy, clayey, gleyed, well water-holding, with high organic matter content, structured chernozems. Strongly boggy and light sandy soils are not suitable.
It tolerates well medium salinized soils with salt concentration up to 0.5%. If soil salinization occurs by 2.5-3% of mass of dry soil and if chlorine content exceeds 0.3%, rice may not grow. Optimal reaction of soil medium is slightly acidic – pH 5-6,6, it also tolerates more acidic reaction, as active acidity decreases under flooding.
According to studies by B.A. Neunylov, cereal grains are able to germinate at lower oxygen concentrations than seeds of other cereal crops. However, strong oxygen deficiency leads to poor development of the root system and above-ground organs. After sprouting, the roots of rice plants are supplied with atmospheric oxygen through well-developed air-bearing tissues.
Vegetation
Most varieties cultivated in Russia have a growing season of 90 to 140 days, the late-ripening ones up to 145 days.
Phenological phases of growth:
- germination;
- sprouting;
- tillering;
- emergence into a tube;
- panicle formation;
- flowering;
- ripening.
Transitions between phases are associated with changes in metabolism and with new morphological formations. Therefore, plant requirements for heat, moisture, nutrients and other life factors change.
Germination
Germination is characterized by swelling of seeds, with absorption of up to 23-28% of water of the seeds’ own weight. Germination can occur without flooding, and the uniformity of seedlings increases.
Germination occurs by sprouting the germ with transformation into a young plant. The growth cone (0.06 mm), coleoptile, and first true leaf appear first. At 16-20°C the duration of the phase is 10-12 days, at early sowing and 12-14°C it is 14-16 days. Rice seeds can swell in a medium without oxygen, the need for it appears later – when the germinal root and leaves grow.
Sprouting
The sprouting phase lasts until 3-4 true leaves are formed. It begins with the growth of axillary buds and root-forming tissue from the meristem.
Then, differentiation of leaves and adventitious roots in the zone of leaf attachment to the lower part of the internode occurs. At the end of growth, the upper leaves are established.
A water layer of 3-5 cm is required for the establishment of the tillering node, since the node is formed almost at the soil surface.
Tillering
The tillering phase begins with the formation of 3-4 leaves, lasts 25-30 days, and ends at 8-9 leaves. The growth cone grows intensively, the axis of the rudimentary panicle and the tubercles of its branches stand out. This phase is when the foundations of a productive panicle are laid: the longer the growth cone, the more branches are formed and the more productive the panicle.
Emergence into the tube
The emergence phase into the tube begins with the emergence of 9-10 leaves. Growth of straw internodes takes place. Intensive growth of plants and their organs is observed. There is a pronounced growth of rudimentary branches of the panicle, the branches of the second and next orders, as well as spikelet tubercles are established. According to Fenelonova T.M., water temperature below 20 °C leads to extension of the process of panicle formation and increases the number of set branches and spikelets on panicle by 15% compared to temperature of 30 °C. Reduction of water temperature can be achieved by increasing its layer or intensity of flow.
Panicle formation
In the phase of panicle formation, a rice inflorescence emerges from the sheath of the upper leaf.
Flowering
The flowering phase begins simultaneously with hatching and lasts 5-7 days. Varieties released in Russia have closed and open flowering.
Ripening
The ripening phase is divided into milky, waxy, and full ripeness. The duration is 30-40 days, depending on air and soil temperature.
Rice irrigation system
In Russia, rice is grown under flooded conditions, so irrigation systems with professional layout of irrigation cards and checks for uniform flooding and water discharge are important.
Rice irrigation systems include:
- the water-feeding part;
- rice field;
- discharge and drainage systems;
- various hydraulic structures;
- fencing canals.
The irrigation system is constructed on even massifs with slope not more than 0.003-0.005°. The field is divided by longitudinal berms into irrigation cards of 15 to 50 hectares, which are irrigated by irrigation and drained by discharge canals. Irrigation maps are 200-300 m wide and 600-1500 m long. They are divided by transversal rolls 35 cm in height and 160 cm in width at the base and 20 cm on top, dividing them into checks on 3-5 ha of regular configuration and leveled surface with deviation from horizontal no more than ±5 cm, difference in water level within a check – no more than 10 cm.
For uniform overflow of water between checks in transversal rolls recesses are made.
Irrigation cards of Krasnodar type. Card has an area from 12 to 25 hectares and consists of one check, at which on the long side there is an irrigation spillway with a wide front of the bay. After filling the irrigation-discharge water overflows it and comes out on the check-card along its entire length. This approach allows for efficient use of machinery and quick delivery and discharge of water into the same canal. When cards are equipped with automatic water outlets to regulate the water layer, one technician can serve up to 80-120 hectares of crops.
Crop rotation
Rice normally tolerates permanent crops, which are often used in established rice-growing areas since ancient times. However, waterlogging or salinization quickly sets in, aerobic microorganisms become less viable, hydrogen sulfide and iron oxides accumulate, which leads to soil clogging, reduced organic matter content, the spread of specific weeds such as millet (weed), and a drop in yields.
Table. Rice yield in rotation and permanent crops (All-Russian Research Institute of Rice)
| I | 1-2 - perennial grasses; 3-6 - rice | |||||||
| II | 1-2 - perennial grasses; 3-4 - rice; 5 - seeded fallow; 6 - rice | |||||||
| III | 1-2 - perennial grasses; 3-4 - rice; 5 - seeded fallow; 6 - rice | |||||||
At rice cultivation during four years in a row on one field the yield averaged 4.22 t/ha, that on 44% higher, than at permanent crop. Therefore, saturation of crop rotation with rice up to 67-70% is possible, which contributes to increase of its production in specialized farms and increase of payback of capital investments for construction of rice systems. For example, in 1971-1974 in Krasnodar region saturation of rice crop rotations reached up to 80% and rice was sown on 67% of area during 3-5 years in row.
However, with a permanent placement of more than three years – the yield begins to decline. In this case, intermediate leguminous crops for green manure are introduced. In the All-Russian Research Institute of Rice when sowing 4 years in a row after the seeded fallow, the yield was 2.84 t/ha, after the green manure – 4.12 t/ha, when fertilizing the green manure N120P90 – 7.41 t/ha.
Therefore, in 2-3 years, rice should be alternated with other crops that enrich the soil with organic matter and suppress weeds. The best predecessors of rice include alfalfa, clover, leguminous in a seeded fallow (soybeans, peas, mung bean, vetch, etc.), green manure fallow, and intercrops crops for green fertilization. Good predecessors also include cucurbits, root crops, winter wheat and winter barley.
Typical for rice-growing areas crop rotations:
- 1-3 – rice; 4 – leguminous crops (seeded fallow); 5-6 – rice; 7 – winter crops with undersowing of perennial grasses, such as clover or alfalfa; 8 – perennial grasses for silage and green fertilizer. In this special crop rotation, 75% of the area is devoted to cereals, of which rice accounts for 62.5%.
- 1, 2 – rice; 3 – seeded fallow; 4-5 – rice; 6-7 – perennial grasses. The share of rice is 57.1%.
Short-rotation crop rotation: 1-3 – rice; 4 – seeded fallow. The share of rice is 75%. It is used in farms with high culture of farming.
Fertilizer system
Rice responds well to fertilizer application. Per 1 kg a.s. of fertilizer the increase in grain is 9-11 kg. Depending on cultivation zone, rice removes 19.3 kg N, 9.6 kg P2O5, and approximately 25 kg K2O per ton of grain and straw in Krasnodar Territory, and 23.5 kg N, 9.8 kg P2O5, and 31.0 kg K2O in Primorsky Territory. Therefore, to obtain high yields, it is necessary to apply large doses of mineral fertilizers under rice.
Until the tillering phase, rice consumes relatively small amounts of nutrients, but during this period, the rice is very sensitive to the lack of nutrients, especially phosphorus and nitrogen, which is associated with the beginning of the formation of the panicle. Therefore, row fertilization and top dressing are used. The main part of the nutrients: more than 70% of nitrogen, 90% of phosphorus and 80% of potassium comes from the tillering to flowering period.
Rice is also demanding to the organic matter of the soil, which must also have a large absorption capacity to save from leaching of soluble nutrients to the stage of their maximum absorption by plants. For this reason, in addition to embedding root and plant residues of perennial grasses and legumes for green fertilizer, organic fertilizers in doses of 20-40 tons/ra of semi-digested manure under the main tillage in the rotation.
Great effect gives a joint introduction of organic and mineral fertilizers. For example, at the Kuban rice experimental station when growing rice for a number of years on the same field yield was on a background of mineral fertilizers 3.88 t/ha, organic – 4.48 t/ha, with the joint introduction of organic and mineral fertilizers – 5.98 t/ha.
Green fertilization is also of great importance. At the Far East rice experimental station at plowing 20-25 t/ha of green mass of soybean grain yield was 4.45 t/ha, after pure steam – 3.55 t/ha, by clover on green manure – 4.58 t/ha.
Compost and crop waste can be used as organic fertilizers. Shredded straw is also used. According to the All-Russian Rice Research Institute, during harvesting by combines with universal straw choppers ПУН-6, the introduction of rice straw into the surface layer of the soil with simultaneous introduction of nitrogen fertilizer (N180) increased rice yield from 7.05 to 7.86 t/ha and without nitrogen fertilizer – from 4.62 to 4.77 t/ha.
Large amounts of mineral fertilizers are applied to rice for greater irrigation efficiency. Norms of application and ratios of elements are set depending on planned yield, soil type and peculiarities of predecessors.
After all predecessors, aerial feeding (N30P30) is carried out in the tillering phase. Sometimes two feedings are made: the first at the emergence of 3-4 leaves, the second at the tillering phase. Fertilization can also be carried out with irrigation water at a rate of N15-30P20-25K20-25 with a layer of water should not exceed 3-5 cm. After the fertilizer water has been absorbed into the soil, the water layer can be increased to 10-15 cm.
Nitrogen fertilizers are important for rice in the first place, phosphorus and in the last place potassium fertilizers have a weak positive effect and only on the background of nitrogen fertilizers. Phosphorus fertilizers are more effective on heavily ashed soils, potash fertilizers on more gleyed soils.
Table. Recommended rates of mineral fertilizers for rice on meadow-chernozem soils by crop rotation fields for the southern regions of Russia (Krasnodar region), kg/ha a.s.
| Perennial grasses | 1st | |||
| 2nd | ||||
| 3rd | ||||
| 4th | ||||
| Seeded fallow | 1st | |||
| 2nd | ||||
| 3rd | ||||
| 4th | ||||
| Plots to be tilled for a long time | Over 4 years |
High doses of nitrogen fertilizers reduce resistance to pyriculariasis, lead to lodging of crops, sterile spikelets and massive appearance of algae. In this case nitrogen fertilizers are applied fractionally. The All-Russian Rice Research Institute showed that when all nitrogen doses were added (with phosphorus fertilizers) before sowing, yield was 5.18 t/ha, whereas when 2/3 dose was added before sowing and 1/3 in top dressing, yield was 6.12 t/ha. Large doses of manure also lead to lodging of rice.
At short flooding, when sprouts appear at wetting irrigation, losses of nitrogen, applied before sowing, are up to 55%. Therefore, efficient use of nitrogen by plants increases with the introduction of 2/3 of the dose before sowing and 1/3 in top dressing (on the shoots and in the tillering phase), or 1/3 under the preplanting treatment, 1/3 in top dressing at the beginning of tillering and 1/3 in top dressing at the stage of emerging the tube.
When seeds are deeply embedded in the rows, granulated ammonium nitrate at a rate of 50-100 kg / ha and granulated superphosphate is added. Nitrate forms of nitrogen fertilizers are quickly washed from the soil or reduced to molecular nitrogen in anaerobic conditions, so it is better to apply ammonia forms for rice, superphosphate for phosphorus, and potassium – potassium salt or potassium chloride.
Some researchers (A.G. Esipov, B.A. Neunylov, etc.) recommend to introduce lime on soils with high acidity (pH of salt extract 4,1-4,2) by 0,8-1,2 t/ra 2 times per rotation: first – for perennial grasses, second – for rice, which comes after perennial grasses.
On highly saline soils, gypsum application is carried out.
Tillage system
Main tillage
Rice grows slowly at the beginning of its development and is strongly suppressed by weeds. It is usually placed on heavy soils, which are highly compacted by irrigation. Soils flooded with a layer of water accumulate reduced compounds that do not decompose and do not release nutrients without access to oxygen. Soil aeration and oxidation of these compounds is aided by tillage. For this reason, rice is demanding of clean fields and responds to deep and high-quality tillage. According to data from experimental stations, autumn tillage to a depth of 25-27 cm with ploughs with skimmers is advantageous and the upper, strongly clogged layer is better incorporated. Ploughed soil is left in the ridges in the fall for enhanced aeration and drying. In the experiments of the Kuban rice experimental station increase in plowing depth from 20 to 25 cm increased rice yield by 0.41 t/ha.
Sometimes before plowing to control weeds carry out 1-2 discing.
Fields heavily littered with bulrush and arrowroot are plowed to 12-14 cm. In this case, 70-80% of the tubers of these weeds die during the winter from freezing and drying.
When growing rice on saline soils, periodic (once every 3-5 years) plowing with plows with soil ploughs or plows without mouldboards on 40-45 cm is effective. It breaks compacted layer, increases filtration, aeration, oxidation processes and isolates topsoil from capillary moistening by mineralized groundwater.
Two-layer tillage to the depth of 35-40 cm with plough of ПТН-40 type gives a good effect. In the northern part of Sarpinskaya lowland (Kalmykia), after ordinary plowing at 20-22 cm, rice yield was 5.22 t/ha, whereas after increasing the plowing depth to 25-30 cm – 5.52 t/ha, at double-layer processing at 35-40 cm – 6.01 t/ha.
In case of detection of hillocks or depressions on the field in autumn, selective leveling is carried out.
Pre-sowing tillage
In spring, two pre-sowing cultivations are carried out by a chisel-cultivator or a unit consisting of disc and tooth harrows. The first tillage is carried out before the beginning of fieldwork at a depth of 18-22 cm, the second – 5-7 days before sowing at a depth of 12-14 cm with harrowing. 1-2 days before sowing, packing is carried out. Between the tillage the checks surface is leveled by scrapers and graders or special levelers. Quality pre-sowing preparation of the soil increases the yield by 1,5-2,0 t/ha.
Additional weed control by no-till tools with harrowing is also carried out between tillage. Such pre-sowing treatment provides uniform seeding and distribution of water in checks, reduces its filtration.
Sometimes the pre-sowing cultivation to the depth of 6-8 cm with harrowing is limited.
Minimal tillage
Minimal tillage is also used, reducing the depth to 8-12 cm and combining several technological operations: pre-sowing tillage, leveling, sowing, applying herbicides and fertilizers, rolling. For this purpose, combined units are used, for example, a milling cultivator – seeder КФС-3,6, milling machine ФН-1,6, and rotary plow ПР-2,7.
According to the data of All-Russian Rice Research Institute, tillage and sowing by traditional technology gave yield of 5.65 t/ha, milling in autumn and sowing in spring by КФС-3,6 – 6.15 t/ha, without tillage in autumn and sowing by КФС-3,6 on stubble – 6.34 t/ha.
Seeding
Preparation of seeds
In many rice-growing countries, such as China, Japan, the Philippines, and Vietnam, rice is planted by seedlings. In Russia, this method is not used, sowing is done by seeds. Only seeds of the 1st class of large fractions give even and full sprouts. Germination of seeds should be not less than 90%. Special rice cleaners and other sorting-separators are used for seed cleaning.
To get the best quality seeds and isolate the most biologically valuable and heavy fractions, they are sorted by density in a saturated solution of ammonium sulfate, consisting of 6-27 parts (NH4) 2SO4 in 100 parts of water (5-21% solution). Stubby grains and seeds of weed plants (rice weevil, monochoria bolls) float and full-grown grains settle down.
To accelerate the emergence of seedlings and increase field germination, seeds are soaked or germinated before sowing. When soaking them immersed in water and kept 2-3 days at 18-20 °C (20-25 °C (Niklyaev V.S.), 25-30 °C (Kolomeychenko V.V.)), then aired until free-flowing. For germination the seeds are kept for 24 hours in water at 24-26 °C until complete swelling. Then 24-48 hours they germinate in bolls until they emerge, aired and dried in a thin layer in the shade (under direct sunlight incipient seeds die) until loose.
Air-heat treatment for 5-7 days is used to increase germination and germination energy of dry seeds. Air-heat treatment can be replaced by solar heating of seeds 5-8 days before sowing. After treatment, seeds are treated with an aqueous suspension of granosan with dye at a rate of 2 kg of the preparation per 1 ton of seeds.
Ferazim (500 g/l carbendazim) is used for seed dressing against Fusarium root rot and pyridia.
Timing of seeding
The dates of sowing rice are determined by the temperature of the upper layer of soil and irrigation water, which should warm up to 12-15 °C, in the absence of danger of frosts. In Central Asia and Transcaucasia, sowing begins in the second half of April, in the North Caucasus and the Far East, the south of Ukraine, the south of Kazakhstan – in the first decade of May. According to the experimental data of Karatal rice field (Kazakhstan), rice yield at sowing on April 30 was 5.86 t/ha, May 10 – 6.34 t/ha, May 15 – 5.55 t/ha.
Table. Yields of rice varieties depending on sowing dates, 100 kg/ha (Kazakh Research Institute of Rice)
| April 15 | |||
| May 5 | |||
| May 15 | |||
| May 25 | |||
| June 5 |
The early maturity of the variety affects the timing of planting. The faster-ripening varieties can be sown a little later, but they also reduce yields sharply if sown after May 15. Late-ripening varieties are sown earlier.
Sowing methods and depth
The main method of sowing rice is the row sowing with seed depth of 1.5-2 cm and immediate flooding with a water layer of 5-7 cm. The narrow-row sowing method is also used. Before sowing, the soil is rolled with smooth rollers. Seeder coulters are retrofitted with limiting flaps so that the sowing depth does not exceed 2 cm. The area and configuration of the card-checks also allow using a cross-sowing method. According to the experiments of N.I. Klushina in the Krasnodar Territory, the yield of rice with the scattered method of sowing was 5.11 t/ha, with the row planting – 5.65 t/ha, with cross-sowing – 6.23 t/ha. Cross-sowing and cross-diagonal methods are widely used in Kuban.
The Far Eastern Rice Experimental Station offers an early method of sowing rice when the soil temperature reaches +8 °С at a depth of 4 to 6 cm. Before sowing, moisture-charge irrigation is carried out, without additional post-sowing irrigation. After the emergence of seedlings, treat the crops with herbicides and, when 2-3 leaves appear, the check is flooded. Yield at early and deep sowing not only does not decrease, but often increases compared to the usual sowing depth at the optimum time. The resistance of plants to lodging increases, and ripening occurs 10-15 days earlier. According to the data of All-Russian Rice Research Institute obtained for 6 years, at early and deep sowing in April, the yield was 6.82 t/ha, at normal sowing and shallow sowing – 6.66 t/ha.
Deep sowing allows to get denser, more uniform sprouts under natural humidity, the plants better develop the root system, increases resistance to lodging. Differentiation of the growth cone occurs at lower temperatures, and the panicle is more productive. Water consumption for irrigation decreases by 15-20%.
Scatter seeding is the least perfect, it implies air seeding on the flooded field. The main disadvantage is that dry seeds have buoyancy and they are carried to the rollers, the sowing turns out uneven. For the spreading method it is more reasonable to use soaked seeds, as they sink better. The advantage of the method is high productivity – up to 120-150 hectares per day. When using soaked seeds and windless weather, scatter seeding is not inferior to seeding.
Seeding rates
The field germination of rice seeds and, consequently, the thinning of crops depend on the timing and methods of sowing, varietal characteristics, seed quality, agrotechnics and irrigation regime. Rice is characterized by high bushiness. If it is well nourished and sown sparsely, one plant can produce up to 70 productive stems. Therefore, the number of productive stems can be adjusted by changing the seeding rate, soil fertility, and intensity of plant care.
Rice seeding rate should ensure the density of plants at the time of harvesting 250-350 per m2 or 350-450 productive stems. At an ordinary sowing such density is reached at the rate of sowing of 5-8 million germinated seeds for 1 ha or 180-230 kg/ha. At deep seeding the rate is increased by 0.5 million grains per hectare, at air seeding – by 1 million. At such rates of seeding it is possible to receive up to 7.0 t/ha of grain. According to the All-Russian Rice Research Institute (N.I. Klushina), when fertilizers (N120P120K60) were applied, the change of seeding rate from 3 to 5 million seeds per 1 ha increased the yield from 6.76 to 7.37 t/ha.
Irrigation and crop care
Rice is grown under irrigation regimes: permanent, shortened, intermittent flooding and periodic irrigation. Permanent and shortened water regimes are used on more than 90% of rice crops in the world.
Permanent flooding
Permanent flooding is used on clogged and saline soils. Throughout the whole vegetation period of rice in the field a variable water layer is created and maintained, the water consumption in this case is up to 30 thousand m3/ha. Seed embedding in this method is usually minimal – 1.0-2 cm. Before the complete emergence of shoots the checks are filled with water in a layer of 8-10 cm, as the plants grow, the depth is increased to 12-15 cm and maintained until the ripening of rice. After that water is gradually released.
To control the ergot, the layer of water in the checks is lifted for 7-8 days to 20-25 cm. At the beginning of the tillering phase, the layer is reduced to 5 cm, then lifted again to 12-15 cm.
Permanent flooding leads to a strong thinning of seedlings – by 75-80%, mainly due to the lack of oxygen in the flooded field, the seeds with low energy of germination die.
Shortened flooding
Rice seeds are not water-resistant, but plants under flooding in the phase of sprouts have elongated leaves, in the phase of tillering – adventitious roots are formed which do not need oxygen in the soil. On this was proposed a shortened method of flooding (B.A. Neunylov et al.).
Under shortened flooding, rice seeds are sown to a depth of 4-6 cm, and moistening irrigation is carried out. Flooding is carried out only after emergence of mass sprouts and herbicide treatment. Water layer is set at 3-8 cm.
After all the plants have come to the surface, the water layer is gradually increased to 12-15 cm. During the tillering period of rice create optimal conditions for the formation of a powerful root system, nodal roots and lateral shoots. To do this, before the beginning of tillering the water layer is gradually reduced, with a slight drying of the checks the crops are treated with herbicides and nitrogen fertilizer. After the water layer is again brought to 12-15 cm and maintained until the wax maturity of grain. Water is discharged in crops of early maturing varieties in the middle of wax maturity, late maturing – at the beginning of wax maturity. In this case, by the end of waxing ripeness, no water remains on the field, and by the time of harvesting, the soil has time to dry out.
The shortened flooding is considered more progressive and is widely used in Russia. Water consumption by shortened flooding is 20-40 thousand m3/ha.
Intermittent flooding
The essence of intermittent flooding is to periodically discharge water during the growing season of plants. For example, the field is flooded for 5-7-10 days, then dumped for 5-7 days. Dumping is not carried out during flowering.
The regime is used on soils with strong filtration to reduce the irrigation rate by 25-30%. It is suitable for non-saline, weed-free fields with a leveled surface. Intermittent flooding improves the air regime, increases the resistance of crops to lodging and suppresses the spread of malarial mosquitoes.
Periodic irrigation
The regime of periodic irrigation is to maintain soil moisture 65-70% of the lowest moisture capacity until the emergence of seedlings, then – 75-80%. Irrigation rate is 800-1000 m3/ha. Methods of irrigation can be different – sprinkling, irrigation, precipitation. Watering from sowing to tillering stage is done in 8 to 10 days, from tillering stage to emerging into a tube – in 6-8 days, then till the end of wax maturity – in 8-10 days. Watering rate is 600-800 m3/ha.
Water is supplied up to 15 times during the growing season, the total consumption is up to 8-10 thousand m3/ha. The number of irrigations and irrigation rates are adjusted depending on the region of cultivation, rainfall, evaporation, etc. Periodic irrigation is used in the cultivation of dryland or wetted rice varieties. However, the method is not widespread due to low yields and economically not justified.
Crop care
On saline soils perform leaching irrigation after autumn plowing. Rice should not be left without water layer to prevent salinization of upper soil layers by rising currents.
When pests (rice mosquito, mineral) are spread, the water layer is reduced to strengthen the seedlings and apply fertilizer. With severe infestation, water is completely dumped and the layer of water is created again only in 7-9 days after the death of larvae.
During the vegetation period, the crops are treated against a number of pests with 40% metaphos at a rate of 0.5 to 0.75 kg of the preparation per hectare.
On rice fields, systematic control of specific weeds is of great importance. For this purpose, regulation of water layer is carried out. Typical weeds in rice fields include Milium (Milium), sedge (Carex), cattail (Typha), bogweed (Alisma), arrowroot (Sagittaria), klebnekamysh (Bolboschoenus).
To control millet (Milium), it is brought to 25 cm and lowered after the leaves of the weeds turn brown.
Herbicides are especially effective on dicotyledons. To kill broadleaf and marsh weeds, such as lapwort (Alisma), arrowroot (Sagittaria), monochoria (Monochoria), clubroot (Bolboschoenus), the crops are treated with 43% 2,4-D butyl ether in the phase of full tillering at a dose of 1.2-1.4 kg/ha. Milkweed (Milium) is treated with 30% propanide emulsion concentrate in the phase of 1-4 leaves at a dose of 16.7-30 kg/ha; the water is discarded from checks before treatment. In 2-5 days after the death of the main mass of weeds, the fields are filled with a layer of water 10-12 cm. Field drying for 5-7 days also gives a good result.
According to the Far Eastern Rice Experimental Station, loosening the field under water increases rice yield by 1.0-1.5 t/ha. Thanks to this, the film of algae, which absorbs oxygen, is destroyed, soil aeration is improved and weed vegetation is eliminated. The treatment should be started as soon as seedlings appear and before the end of the emerging into the tube phase, with 5-7 day intervals.
Sumithion (500 g/l) is used against mosquitoes and ichneumon flies.
Harvesting
The top spikelets in a rice pan are the first to ripen. Harvesting begins when the grains in the middle part of the panicle of the main stalks are at full maturity. This allows 70-80% of the grains to reach full maturity. Earlier harvesting terms lead to an increase in the proportion of friable grains with increased filminess.
It is usually harvested using the biphase method on well drained cards. To do this, rice is mowed in swaths with reapers ЖНУ-4, the height of the cut 10-15 cm. After 3-5 days when the humidity of grain 15-18% swaths are picked up and threshed by special combine on half-track (СКПР-6) or caterpillar (СКД-5Р). Strong drying of grain is undesirable, as it increases the crushing of grain at threshing. Under the influence of alternate moistening and drying of the rolls water content of the grain tissue changes, which leads to their cracking. The same happens during over-ripening at the root. Cracking can reach 20-40%. Such seeds have reduced field germination and give weakened seedlings. According to A.I. Apod, the germination rate of whole seeds is 94%, cracked seeds – 21%. Cracked grains are more prone to break during threshing, technological properties and quality of groats are reduced.
To accelerate drying of rice plants at the root, desiccation – preharvest drying – is used. It is done by spraying with desiccants when 70-75% of grains are fully ripe. Magnesium chlorate is used as a desiccant at a rate of 25-50 kg in 150 liters of water per 1 hectare. In this case grain moisture content decreases to 15-16%, which allows you to begin harvesting rice in one-phase method earlier. This method is used in the Far East after frosts, when plants naturally dehydrate. Single-phase harvesting is used on non-lodged crops with uniform maturity or thinned crops with yields up to 5.0 t/ha, also on non-drained checks.
According to the data of M.A. Alexandrov, after preharvest drying and with single-phase harvesting the grain losses decrease, its seed and marketable qualities improve, cracking decreases by 30%, field germination increases by 12-15%.
On high-yielding (over 4.0 n/ha) and seeded plots to reduce grain losses and injury, rice is usually harvested by single-phase method with double threshing. At the first threshing up to 70-80% of grains as if combed, for which the gap between drum and deck increases to 12 mm at the output, and the frequency of rotation is reduced to 500-650 rpm. Straw with unmilked grains comes out in a roll on the stubble behind the combine, for which the bottom of the opener is removed and a rolling board is installed. After 2-3 days, the windrows are picked up and subjected to the secondary threshing in the usual mode: up to 1000 revolutions per minute and a gap of 4-5 mm at the output. The grain of the first threshing is larger, more mature and less traumatized. The second threshed grain is used for commodity purposes.
The use of special double-drum harvesters, such as СКД-5Р, СКГ1Р-6, allows you to reduce grain losses from unthreshed and damage. They can harvest rice in one pass of the mass at yields up to 5.5 t/ha. The mode of the first drum is 700-720 rpm, the second – 980-1050 rpm.
Rice seeds at moisture above 15% quickly lose germination, so they are cleaned immediately after threshing and dried to 13-14%. For grain drying the installations of active ventilation with heated air are better suited.
The third way of harvesting is stationary threshing, when drying and threshing of the whole cut mass is carried out on a threshing floor.
Progressive cultivation technology
The technology proposed by the All-Russian Research Institute of Rice is used in all rice-growing zones and allows to get up to 5-6 t/ha. It includes:
- autumn plowing of the seedbed to a depth of 12-20 cm;
- pre-sowing preparation of the soil is started at moisture of 20-26% with ploughing by harrow to a depth of 16-18 cm by combined units;
- the second loosening is carried out 8-12 days after the first 12-14 cm for cutting weeds;
- in areas of low fertility, semi-digested manure is applied with РУН-15Б;
- repeated plowing at a depth of 10-14 cm;
- discing with simultaneous harrowing БДТ-7 and ЗБЗТС-10;
- for levelling checks and operational leveling of the soil with an accuracy of ±5 cm is carried out Д-541А;
- in the main fertilizer is made 5-6 days before sowing and flooding with embedding to a depth of 10-12 cm;
- in the first decade of April perform pre-sowing levelling of checks in diagonal-cross direction in two tracks ШВ-6,0 and ЗККШ-6,0;
- at soil moisture not higher than 25% do roll ЗКВТ-1.4;
- from April 25 to May 5, at soil temperature 12 °C conduct sowing, the depth of seeding – 1.5-2 cm planters CPH-3,6;
- after sowing, cut drainage slots by 10 cm into the peripheral groove;
- apply soil herbicides with ПОУ;
- first flooding to full moisture saturation is done immediately after sowing (May 7-8) with 0,8-1 cm layer of water when applying soil herbicides, without applying soil herbicides – 6-8 cm; the water layer is left until the
- appearance of rice pips;
- nitrogen fertilizer application at the rate of 8 mg of nitrogen per 1 plant;
- checks are slightly dried and aerial treatment with herbicides is carried out;
- to suppress weeds, in 48 h the checks are flooded so that weed leaves are under water and rice leaves are above water;
- in the phase of 2-3 leaves make the second feeding – 10 mg of nitrogen per 1 plant;
- if necessary, in the phase of 4-5 leaves make the third feeding – 12 mg of nitrogen per 1 plant;
- in the phase of 7 leaves, the crops are treated against pyriaculum and marsh vegetation;
- in case of nitrogen deficiency at the phase of 7-9 leaves, make the fourth top dressing;
- at the stage of panicle formation (7-8 leaves) water layer is brought to 25 cm to create an optimal temperature in the tillering node area;
- then at 8-9 leaves the water layer is reduced to 15 cm;
- to accelerate maturation and improve the quality of the seeds at the end of the milky state make senication: the crops are treated with a solution of 60 kg of superphosphate and 15 ml of amine salt 2,4-D in 120-170 liters of water;
- at the end of wax maturity to dry rice, desiccation is done: 15-30 kg/ha of magnesium chlorate by aerial spraying.
During pre-harvesting, the water layer is reduced by 1 cm per day. Checks are dried and mowed. When 85-90% of the ears in the panicles are at full maturity, the rice is mowed. When the windrows dry up, threshing or direct harvesting is carried out, for example, СКД-6Р, СКГД-6. The first threshing is done in soft mode, the second – in hard mode.
Post-harvesting of grain is carried out on the lines ЗАВ-40, КЗС-50. Straw is pulled down, pressed and stubble remains are removed, for that ПФ-0,5 or ПС-0,6 are used.
The given technology was introduced in the Krasnodar region (rice farm “Krasnoarmeisky”). Labor costs for production of 100 kg of rice amounted to 1,9 man-hours with profitability of 87,3%. Form of payment of labor – chord-premium for quantity and quality of production.
Sources
Crop production / P.P. Vavilov, V.V. Gritsenko, V.S. Kuznetsov and others; Ed. P.P. Vavilov. – 5th ed., revised. and additional – M.: Agropromizdat, 1986. – 512 p.: ill. – (Textbook and textbooks for higher educational institutions).
V.V. Kolomeichenko. Crop production / Textbook. — M.: Agrobusinesscenter, 2007. — 600 p. ISBN 978-5-902792-11-6.
Fundamentals of agricultural production technology. Agriculture and crop production. Ed. V.S. Niklyaev. – M .: “Epic”, 2000. – 555 p.