WHEAT is grown in many parts of the world, and the methods of cultivation, the yield per acre, and the nature of the product vary greatly. The most suitable soil appears to be a light clay or a heavy loam, but many others are very productive when climatic conditions are favourable. According to the Census Report already referred to, the seed, in order that there may be a good crop, " must germinate and the young plants grow during the cool and moist parts of the year, which season determines the ultimate density of growth on the ground, and consequently mostly deter mines the yield. . . . Wheat branches only at the ground and pro duces no more heads than stalks. It only sends out these branches early in its growth or during cool weather, and unless the growth is comparatively slow the branching of wheat (called ' must take place before the plant attains any considerable height or it does not occur at all." On the other hand, " wheat ripens in the warmer and drier parts of the year, which season more largely determines the quality, plumpness and colour of the grain. . . . More sun is needed and less rain. Too much rain, particularly if accompanied with heat, induces rust, mildew and other diseases, and too dry winds shrink the grain." Many investigations have been made as to the exact amount of heat required by wheat, but no pre cise result has as yet been obtained, though it is believed that a temperature of at least 41° F. is necessary before vegetative growth can begin. The temperature, measured by day degrees, 1 which
must accumulate before wheat will ripen, appears to vary in different parts of the world according to the length of the day, the amount of precipitation, and the nature of the soil. In England, wheat ripens as a rule when the accumulated temperature amounts to 1,960 day degrees (F.), but in some parts of Alaska, where the days are long, only 1,320 day degrees (F.) are necessary. In sub-tropical countries wheat is a winter crop, the summers frequently being too hot or too dry.
With regard to rainfall a mean annual precipitation of about 15 inches may generally be regarded as a minimum, except under special conditions, as, for example, when all the rain falls during the growing season, or when irrigation or dry farming is practised.
The quality of wheat varies with the conditions under which it is grown. The soft winter wheats, which grow in mild moist districts, such as Western Europe, are relatively rich in starch, while hard wheats—whether winter or spring—which grow in regions where the summers are hot and precipitation is light, are poor in starch, but rich in gluten, and are particularly adapted for milling purposes. In various parts of the world, attempts—all more or less successful— are being made to adapt the grain more closely to its environment and to render it more suitable for the purpose for which it is required.