Durum wheat is produced in western Minnesota and the adjacent eastern portions of the Dakotas. These extra hard wheats are grown primarily for the making of semolina, a coarse meal from which are manufactured the various edible pastes such as macaroni, spaghetti, vermicelli, and noodles. Much is milled and manufactured in America and some is exported.
The white wheats occupy a small district in New York and adjacent Ontario, and larger districts in the Pacific Northwest and in California. They are used for making pastry flours and for blending with harder wheats in the making of bread flours. Large quantities are exported.
The wheat-growing areas of the United States may be divided climatologically into humid (more than 3o inches of precipita tion), semi-arid (25-30 inches), and arid (less than 25 inches). In the humid areas, soft red winter wheat is grown in a rotation with corn and hay or pasture. In the semi-arid Great Plains area, the hard red winter wheat and the hard red and durum spring wheats are grown in rotation to some extent with corn or sorghums, and to a small extent with legumes, such as alfalfa, sweet clover, and red clover. In the arid region west of the Rocky Mountains the precipitation of two years is necessary to produce one crop of wheat. The land is bare-fallowed in the alternate season to con serve moisture for the succeeding crop. Very little rotation of crops can be practiced.
In general, wheat is a cool-weather plant. About two-thirds of the American wheat crop is of winter varieties, germinating and making vigorous root growth with diminishing temperatures in the fall, and vigorous shoot growth with the slowly increasing tem peratures in the spring and early summer. Spring wheats must be sown as early as possible, just as soon as the frost is out and the land can be worked, so that their early growth may be in cool weather. Ripening occurs in warm to hot weather.
The northern limit of successful production of winter wheat has been moving steadily northward during the last fifty years. North Dakota is now the only one of the wheat-growing States of the northern boundary which does not produce winter wheat. The
production of hard red winter wheat extends across the Cana dian boundary from Montana into southern Alberta. The north ern limit of spring wheat production also is moving north with the development of earlier varieties and better methods.
Wheat grows best on relatively heavy soils, such as clays, clay loanis, and loarns, but does not do well on sandy loams, and sands, to which rye is much better adapted. In general, the higher the fertility of the soil the better the wheat yields.
The wheat crop is subject to many hazards during its growth and harvesting. Some are climatic others are biologic. The chief climatic hazard is winterkilling, due to one or more of several causes, including fall drought, winter drought, alternate freezing and thawing, soil blowing, low temperatures without snow cover, and smothering by ice. Other causes of climatic injury are spring or summer drought, hot winds, hail storms and wind storms. Among the chief biologic factors are rodents, insects and fungous diseases. Rodents usually are not very destructive to wheat, although squirrels, rabbits and prairie dogs take their annual toll. Insects often cause heavy losses. The most destructive are Hes sian fly, joint worms, aphids ("green bugs"), grasshoppers, white grubs and wire worms. Fungous diseases may be tremendously de structive. The heaviest losses are caused by two stinking smuts, loose smut, stem rust, leaf rust, seedling blights, scab and foot-rots, although rust-resisting wheat is now cultivated.
Average yields of all wheat in the United States vary around 14.5 bushels per acre. This often is cited against America because yields in England and Germany are rather more than double this quantity. There is no fair comparison. England and Germany are both wholly in the cool humid climate so favourable to wheat. The United States, with its enormous area, covers much territory which is relatively hot and dry, and where yields naturally are low. American farmers, using large-scale machinery and much land, produce enormously more wheat per man than the farmers of Europe, where land is scarce, wages are lower, and much hand labour is used.