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maize (Zea mays ), a species of annual herbaceous plants of the family Gramineae. The species is divided into nine botanical groups according to the internal structure and morphology of the kernel: flint corn (Z m. indurata), dent corn (Z m. indentata ), semident corn (Z. m. semidentata; the most widely cultivated), popcorn (Z. m. everta ), sweet corn (Z. m. saccharata ), flour corn (Z. m. amylacea ), starchy-sweet corn (Z. m. amyleosaccharata ), wax corn (Z. m. ceratina; occupies limited areas), and pod corn (Z. m. tunicata; not used commercially). The corn grown today highly cultivated, incapable of self-seeding and of growing wild.
Corn is a monoecious plant with dioecious inflorescences. It has a straight stalk, 50-80 cm to 5-6 m high, that sometimes bushes. It has a filamentous root system that reaches depths of 100-150 cm. Thick, sturdy brace roots form on the lower above-ground joints of the stalk and keep the plant from lodging. When the moist soil hills up, the roots provide the plant with water and nutrients. The leaves (from eight to 42) are regular, broad-linear, and undulate. They are downy on the upper surface. The male inflorescence (on the top of the stalk) is a panicle; the female (in the axils) is a compound spike usually called the ear (4-50 cm long and 2-10 cm in diameter; weight, 30-500 g). One or two (less commonly, three) ears develop to maturity on each plant. The fruit is a caryopsis; the kernels weigh 50-1,100 g (usually 100-00 g) per 1,000.
The growing season lasts from 90 to more than 150 days. Under field conditions, the shoots usually appear within ten or 12 days. Corn is a warmth-loving plant. The seeds of most varieties and hybrids germinate at about 10°C. The shoots can tolerate frosts to 5°-6°C. New leaves sprout after another week. The ideal temperature for the growth and development of the plant is 20°-24°C. Autumn frosts (- 3°C) are fatal. Corn is a shortday plant and requires intense sunlight. It should therefore be planted on southern slopes, especially in northern regions. The plant consumes the most water and accumulates about 80 per-cent dry substance in a four-week period beginning ten or 12 days before the ears appear. At a yield of 50-55 quintals per hectare (ha) the kernels remove from the soil 150 -170 kg N, 50-75 kg P2O5, and 140-180 kg K2O. The plant uses most of the nutrients in the second half of summer.
Corn responds to organic and mineral fertilizers with high yields on chernozem, gray-forest, chestnut, and soddy-podzolic soils. The plant’s geographic range is determined mainly by temperature conditions. The great diversity of varieties and their use for silage at the milky-wax stage have made it possible to enlarge corn’s zone of cultivation considerably. Corn is grown on all continents from 58° N lat. to 40° S lat.
Corn is a highly productive crop and is used in a variety of ways. The kernels contain 9-12 percent protein, 4—6 percent fat (about 40 percent in the embryo), 65-70 percent carbohydrates, and, in yellow-kernel varieties, a great deal of provitamin A. Corn is used in the food industry (for flour, groats, corn flakes, and popcorn) and by the cornstarch and corn syrup, beer, alcoholic beverage, and canning industries. It is of great importance as a fodder crop. The grain is valuable concentrated fodder and raw material for the mixed feed industry; the green parts and silage from the stems, leaves, and cobs at the milky-wax stage are highly nutritious. Paper, linoleum, viscose, insulating materials, artificial cork and motion-picture film are manufactured from the stalks, cobs, and husks. Corn oil is nutritious, rich in vitamin E. The stigmata contain sitosterol, stigmasterol, fatty oils, essential oils, saponins, bitter glycoside, vitamins C and K, and gummy substances; they are used in the form of decoctions and infusions as hemostatics and as cholagogues and diuretics for cholecystitis, cholangitis, and hepatitis.
Corn was first grown in Central and South America. Well before the discovery of America by the Europeans, the local populations cultivated the crop, from southern Chile to southern Canada. It was imported to Europe at the end of the 15th century, and it spread through the temperate and subtropical areas in the 16th century. It was introduced in Russia in the 17th century, but until the second half of the 19th century it was grown there only in kitchen gardens.
The total area sown to corn in 1971 worldwide was more than 110 million ha. The total grain yield was more than 300 million tons, and the average yield per ha was 27.3 quintals (54.5 quintals per ha in the USA, at 25.8 million ha; 36.1 in Hungary, at 1.36 million ha; 30.5 in Yugoslavia, 2.4 million ha; and 12.0 in India, at more than 5.8 million ha). Corn is grown mainly in the USA, Brazil, Mexico, India, Argentina, Rumania, Yugoslavia, and Hungary.
In the USSR, corn grown for grain occupied 3.3 million ha in 1971 (3.7 million in 1940,4.8 million in 1950, 5.1 million in 1960, and 3.2 million in 1965). Corn grown for silage and green fodder occupied 17.8 million ha. The total grain yield came to 9.4 million tons, averaging 25.7 quintals per ha (13.8 in 1940 and 1950, 19.3 in 1960, and 25.3 in 1960). Corn is grown in the Ukraine, Moldavia, the Northern Caucasus, the Volga Region, Siberia, the Central Chernozem Region, the Urals, the Far East, Transcaucasia, Middle Asia, Kazakhstan, Byelorussia, and the Baltic Region.
The best varieties and hybrids are cultivated in the USSR; 117 were zoned in 1972, including 15 varieties of sweet corn. The practical use of heterosis brought a new stage to corn breeding. The best doublecross interline and varietal-line hybrids compare favorably in productivity and other economically valuable properties with ordinary varieties. The yielding capacity of many of these hybrids exceeds that of common varieties by 20-30 per-cent. Early-ripening and relatively cold-resistant hybrids were zoned in the new corn-growing regions (Byelorussia, the Ukrainian Poles’e, and the nonchernozem zone for the nongrain mass (with the ears at milky-wax ripeness). These corns include the Bukovina 2, Bukovina 3, VIR 25, Dnieper 56, Dnieper 247, and Voronezh 38 hybrids and the Voronezh 76, Voronezh 80, Sterling, and North Dakota varieties.
The most productive corns for grain and silage in the main corn-growing regions (Ukraine, Moldavia, Northern Caucasus, Volga Region) are the midseason-maturing and comparatively drought-resistant hybrids VIR 42, Dnieper 320, Krasnodar 436, and Odessa 50 and the Transcaucasian Yellow-Dent. The mid-season-maturing hybrids VIR 156, Dniepe 90, and Krasnodar 309 and the Odessa 10 variety are the most suitable for irrigated regions. Popcorn (the Dnieper 921 hybrid, the Zhemchuzhnaia 227, and the Risovaia 219) and sweet corn (Kubanskaia Konservnaia 148 and Ranniaia Zolotaia 401, the hybrid Dnieper 664, and Zaria) are grown for the food industry.
The best precursor crops for corn are winter crops, grain legumes, row crops, and, in some parts of the USSR, spring wheat. From ten to 35 tons per ha of manure (depending on soil conditions) should be added. The following amounts of mineral fertilizers should be added at the time of the main plowing (in kg per ha): 30-60 N and P2O5 on ordinary chernozems; 30-45 N, 45-60 P2O5, and 30-45 K2O on leached chernozems and gray forest soils; and 45-60 N, 45-60P2O5, and 35-45 K2O on soddy-podzolic soils. The following amounts should be added at planting time (in kg per ha): 7-10 N, 5-12 P2O5, and 7 K2O.
Corn should be sown when the soil temperature has reached about 10°-12°C. It is sown by the square-nest or rectangular-nest method. The space between the rows should be 60, 70, 90, or 140 cm, and the distance between hills, 70 cm. On weed-free fields, corn can be sown by the single grain method, at 20,000-60,000 plants per ha when grown for grain and silage and 150,000-200,000 per ha when grown for green fodder. The seeds should be planted at a depth of 6-12 cm. The principal cultivation techniques include harrowing, cultivating the spaces between rows to various depths, applying herbicides (atrazine, simazin, 2,4-D), and, in dry regions, irrigating (four or five times during the growth and development stage, irrigation rate, 600-1,000 cu m of water per ha). For grain, the corn should be picked when fully ripe at harvest time, and for silage, at the stage of milky-wax ripeness. Soviet industry manufactures machines for the various zones that eliminate manual labor in corn growing.
Corn pests include the wireworm, the false wireworm, the cutworm caterpillar, the European corn borer, and the corn earworm. Corn suffers from such diseases as corn smut, loose smut, fusarial wilt, cob rot, and white rust.
REFERENCESGarin, K. S., V. D. Koval’, and N. K. Shul’ga. Oroshenie kukuruzy. Moscow, 1962.
Gitalov, A. V. Kompleksnaia mekhanizatsiia vozdelyvaniia kukuruzy. Mosocw, 1962.
Zubenko, V. Kh. Kukuruza v poukosnykh i pozhnivnykh posevakh. Moscow, 1963.
Hruška, J. Monografiia o kukuruze. Moscow, 1965. (Translated from Czech.)
Kozubenko, V. E. Selektsiia kukuruzy. Moscow, 1965.
Osnovy selektsii i semenovodstva gibridnoi kukuruzy. Edited by B. P. Sokolov. Moscow, 1968.
B. P. SOKOLOV and D. S. FILEV