an annual plant whose normal development requires overwintering, that is, exposure to a low temperature (0°-10°C) for 30 to 70 days or longer. Winter crops are planted in the autumn, and their grain is harvested the following year. Winter crops planted in the spring develop a root system and aboveground such vegetative organs as leaves and tillering shoots, but they do not bear fruit. Vernalized seed planted in the spring produces a crop in the same growing season. Winter crops have two periods of active vegetation: autumn (45 to 50 days) and spring-summer (75 to 100 days). Between these periods the plants are dormant. In the autumn, as a result of complex biochemical and physiological processes, the plants harden, that is, become resistant to low temperatures and other unfavorable wintering conditions. There also are forms that are not winter crops and not spring crops. Such plants, which include some varieties of wheat, oats, and barley, may be cultivated in the autumn or spring. They develop normally and produce grain.

Winter crops include such cereals as winter wheat, rye, and barley. A number of oil plants from the family Cruciferae, including winter rape, wintercress, and falseflax, are winter crops. An example of a winter legume is hairy vetch. In world agriculture, winter wheat is the most common winter annual. It is the principal grain crop of Europe and the United States. Winter rye is raised in Europe, the United States, Turkey, Canada, and Argentina. Winter barley is grown in the southern regions of Europe and Asia. Winter rape is cultivated in India, Japan, the German Democratic Republic (GDR), France, Sweden, North Africa, and the United States. Wintercress is grown mainly in the GDR and the Federal Republic of Germany, and false flax in Western Europe and North America. Hairy vetch is raised in Europe, Asia Minor, the United States, and Japan. The raising of winter crops is confined to regions with relatively mild winters and a constant snow cover.

Winter wheat is grown throughout the USSR, from Southern Arkhangel’sk Oblast to the Turkmen SSR. The major regions for its cultivation are the Ukraine, the Northern Caucasus, and Moldavia. Winter wheat covered 8.3 million hectares (ha) in 1913, 14.3 million ha in 1940, 12.1 million ha in 1960, 15.5 million ha in 1970, 20.7 million ha in 1971, and 15.0 million ha in 1972. Winter rye is also grown almost everywhere in the USSR, but more than 70 percent of the sown area is in the RSFSR. It occupied 29.1 million ha in 1913, 23.1 million ha in 1940, 16.2 million ha in 1960, 10 million ha in 1970, 9.5 million ha in 1971, and 8.1 million ha in 1972. Winter barley is grown in the southern RSFSR, Middle Asia, and Moldavia. Winter oil crops are raised in the Ukraine, and hairy vetch in the Ukraine, Byelorussia, and Middle Asia.

In the principal growing regions, the winter crops are higher yielding than the spring ones, since they make better use of the spring moisture supply in the soil. For example, the average winter wheat yield in the USSR (1966–70) was 19.6 quintals per ha, and the average spring wheat yield was 11.1 quintals per ha. In planting in feed rotations, winter rye produces the earliest green feed. Winter crops are particularly valuable because they are good predecessors for spring plants and they cut down on the amount of field work necessary in the spring and during harvesting.