102 THE WHEAT INDUSTRY 



location or topography. Though irrigation adds 

 materially to the cost of production, it reimburses 

 the outlay by giving much greater returns per 

 acre. On the whole the amount of wheat raised 

 under irrigation is small. Yet in many valleys 

 in the Western states it is an important industry. 

 The greater part, however, of the wheat of com- 

 merce is grown under natural rainfall conditions. 



The Soil and Wheat Production. - - Wheat 

 thrives well on a number of soils of widely differ- 

 ent characteristics, ranging from those of heavy 

 clay to those of light sandy content. Its adapta- 

 bility to different climatic and soil conditions 

 makes possible its extensive cultivation. In the 

 United States the soils of the principal wheat- 

 growing area are of four general classes. These 

 are glacial drift, loess, high plains soils, and 

 valley bottom soils. Generally they are all rich 

 in the elements needed as food by the wheat plant, 

 and contain them in available form. Where 

 winter wheat is grown, silt loam soils are favored, 

 as they are somewhat less liable to heaving than 

 the more friable sandy loams. Heaving of the 

 soil is caused by successive freezing and thawing. 

 This often partially uproots the wheat and causes 

 it to be winterkilled. 



Ordinarily soils that are adapted to wheat are 

 also suited to corn and other cereals. Climate 

 and prices are the chief controls which determine 



