246 THE SMALL GRAINS 



through summer tillage or other means. It is there- 

 fore important that plant-foods shall also exist in con- 

 siderable abundance in the lower layers, to the depth 

 of 3 to 6 feet, for solution by the subsoil water, and that 

 the crop plants shall be deep rooted. 



260. Soil water. After all is said as to soil structure 

 and composition, it is clear that the most important con- 

 stituent of any soil is the water it contains. The food of 

 the richest soil is unavailable without it, and, on the 

 other hand, with it, in unrestricted movement, almost 

 the poorest soil will furnish nutriment for a fair crop, 

 extreme conditions, such as presence of toxins, of course 

 excepted. The water supply for cereal crops is of partic- 

 ular importance, as so large a part of the world produc- 

 tion is grown in regions of comparatively low rainfall. 

 In all these regions the necessary mineral constituents being 

 usually present in abundance, as previously shown, the 

 value of different soils may be measured, practically, by 

 their water supply. However, in the humid areas also, 

 there is often a serious lack of available water, and periods 

 of drought occur, which, for these areas, appear equally 

 severe to those occurring in drier regions, where the 

 actual precipitation is much less. In the humid areas, 

 the soil structure and topography of the land are such that 

 much water is lost before reaching the roots. Also be- 

 cause of the greater water requirements of the adapted 

 crops, than in drier areas, a drought of equal intensity 

 apparently causes greater injury. 



261. Variation in water supply in different soils. 

 There is probably no agricultural subject about which 

 there are so many conflicting ideas and theories as the 

 question of the best kind of soil for crop production. At 

 the same time, information on this subject among agron- 



