the raising of agricultural crops under conditions of irrigation. It is one of the most intensive types of farming, and it developed in desert, semidesert, and arid zones and in regions that have inadequate moisture at certain times of the growing season. Very high guaranteed yields of agricultural crops are obtained by irrigation farming (65–70 quintals of wheat, 80–100 quintals of rice, and 40–50 quintals of raw cotton per hectare); they are 3–5 times higher than in dry farming. Repeated sowing (mainly of fodder crops) and inter-planting are used extensively, making possible the most productive use of land and provision of livestock with fodder. In the world as a whole, irrigation farming occupies about 16 percent of the area under cultivation, but it produces as much as the unirrigated area.
Irrigation farming has been known since the Neolithic period. In hot, dry regions (for example, Mesopotamia) and the states of Middle Asia and Egypt, the first centers of farming culture emerged on lands that were inundated annually by spring flooding of rivers. Seeds were sown in the deposited silt after the waters receded, and this made possible the growing of plants without tilling the soil. Hoe farming, the first form of irrigation farming, took shape in this way. The natural flow of the rivers either failed to provide annual flooding of the same sectors or kept them under water too long. Therefore, the ancient farmers built ridges to protect their fields or supplied water to them by canals (primitive systems of flooding irrigation). Large irrigation systems were built in slaveowning societies. In Mexico another method of irrigation was used; the land was brought to the water by raising plants on rafts (chinampas) onto which soil was sprinkled. On the territory of the USSR, the first centers of irrigation farming were in Middle Asia, Transcaucasia, and Southern Siberia (the Minusinsk and Tuva basins).
As of 1972, the total world area of irrigation farming was more than 225 million hectares (ha). Irrigation is used primarily for raising cereal crops (rice, wheat, corn, millet, sorghum, and legumes), industrial crops (cotton and sugarcane), fodder crops, vegetables, and fruit. In most countries irrigated lands constitute 1–15 percent of the cultivated area (the USA, Mexico, Italy, France, Rumania, and Poland); in a number of countries half or more of the cropland is irrigated (Afghanistan, the Socialist Republic of Vietnam, and Iran). In a few countries only irrigation farming is possible (Egypt, Saudi Arabia, and Oman). Irrigation farming is also developing in Great Britain, the Federal Republic of Germany, Belgium, and other countries located in regions of adequate and excess moisture.
The main regions of irrigation farming in the USSR are (1) the Lower and Middle Volga Regions, the Trans-Volga Region, and the Northern Caucasus (irrigated lands are occupied by wheat, rice, sunflowers, fodder crops, vegetables, fruit, and grapes); (2) the Far East (primarily rice); (3) the southern oblasts of the Ukraine (wheat, rice, corn, sugar beets, vegetables, fruit, grapes, and potatoes); (4) the republics of Middle Asia and Kazakhstan—the Golodnaia and Karshi steppes, the Karakum Canal zone, the Kyzylkum massif, and the Vakhsh, Gissar, and Fergana valleys (cotton, rice, alfalfa, wheat, and sugar beets; orchards and vineyards); (5) Transcaucasia—the Ararat Valley and the Kura-Araks Lowland (vineyards and orchards; cotton and vegetables). In addition, vegetables, fruit, and fodder crops and meadows and pastures in the nonchernozem zone and the Central Chernozem Zone of the European part of the USSR are irrigated during dry years and seasons. In 1972 the sown area of irrigation farming in the USSR was 9,353,000 ha (see Table 1).
In 1972, yields from irrigated lands in the USSR were as follows (in tons): grain, 5,717,000 (including 1,647,000 of rice); raw cotton, 7,296,000; sugar beets (factory), 5,068,000; vegetables, 6,908,000.
Irrigation systems are built to raise agricultural crops in irrigation farming; rice is raised in special rice systems. The disposition of sown area is narrowly specialized. Crop rotations are saturated with the leading crop. A crop rotation with two or three fields of winter wheat has been introduced on farms in the irrigation zone of the southern Ukraine; the remaining area of the rotation is occupied by sugar beets, alfalfa, corn, and so on. The rice rotation (five fields of rice, 60–65 percent of the area of the rotation) and cotton rotation (five to six fields of cotton,
|Table 1. Use of Irrigated land in the USSR (hectares)|
|Cereal crops..................||1 892,000||2,216,000 2 244 000||2,422,000|
|Industrial crops.................||2,382.000||2,705,000 3,029,000||3,017,000|
|Potatoes, vegetables, and melons......||492.000||596,000 698,000||766,000|
|Fodder crops..................||1,612,000||1.737,000 2,669,000||3,147,000|
|Orchards and other perennial plantings . .||638.000||889.000 989.000||1,031,000|
|Hayfields and pastures............||366.000||526,000 298,000||485,000|
|Total .....................||9.302,000||9,812,000 10.891,000||11,774,000|
60–75 percent), in which fields of the primary crops alternate with alfalfa, legumes, and corn, are distinguished by high stability. Correct watering times and rates, which depend on climatic and soil conditions and on the characteristics of the crop and variety, are very important in the technology of raising irrigated crops. Watering changes the conditions for performance of all scientific-farming procedures, thus affecting the efficiency of such procedures, and this in turn exercises a major influence on the use of irrigation water by plants.
Soil tillage in irrigation farming includes primary (capital) leveling and ongoing leveling (that is, leveling the soil surface for even distribution of water over the irrigated area), fall plowing (to 30–35 cm) and presowing soil tillage, field preparation for repeated sowings, and soil management during the growing season (tillage after watering in row crop fields and grading the temporary irrigation network, which consists of temporary irrigation canals, field ridges, and irrigation furrows or strips). Irrigation farming creates favorable conditions for increasing the effectiveness of fertilizers, which improve the use of irrigation water by plants. With irrigation, fertilizers are assimilated faster and used more fully by the crops, because water increases the activity of biological processes and chemical transformations in the soil. Healthy development of the root system and surface organs of irrigated plants also promotes rapid absorption of nutrients. In irrigation farming, doses of mineral fertilizer are increased (usually by 30–50 percent), and the higher the irrigation rate, the greater the increase. Manure is also applied for corn, potatoes, vegetables, and perennial plantings (20–40 tons/ha); green fertilizer is also used (mung beans, soybeans, Persian clover, and seradella are planted as green manure crops).
Irrigation introduces many special characteristics into the technology of planting and caring for crops—for example, an increase in the planting rate of 10–15 percent for grain crops and by a factor of 2 (sometimes 3) for row crops and coordination of the direction of rows for planting and irrigation. Special steps are taken in irrigation farming to combat irrigation erosion, development of marshy land, and salinization of the soil. Under irrigation conditions the highest yields are produced by intensive varieties that have standing power and are responsive to fertilizers and irrigation and resistant to diseases and pests. Examples are the Bezostaia no. 1, Mironovskaia Iubileinaia, Avrora, and Kavkaz varieties of winter wheat, which produce 80–100 quintals of grain per hectare.
REFERENCESBiologicheskie osnovy oroshaemogo zemledeliia [Sb. statei]. Moscow, 1966.
Oroshaemoe zemledelie. General editor, B. A. Shumakov. Moscow, 1965.
Zemli drevnego orosheniia i perspektivy ikh sel’skokhoziaistvennogo ispol’-zovaniia. Moscow, 1969.
Lysogorov, S. D. Oroshaemoe zemledelie, 3rd ed. Moscow, 1971.
S. D. LYSOGOROV