82 



WATER IN SOILS 



Wheat requires a little less water than the other small grains. 

 It has been shown by King that if the rainfall be well distributed 

 through the growing season twelve inches is sufficient to produce 

 a heavy yield of wheat. Wheat is grown in some regions where 

 the rainfall is too light for a number of other field crops. Note 

 the management illustrated in figure 63. 



The most important lesson, however, to be learned in the 

 study of crop requirements is the fact that the rainfall is not 

 evenly distributed and that regions with twenty or thirty inches of 

 annual rainfall will not produce good yields of wheat, or corre- 

 sponding yields of other crops. So much of the rain comes at a 

 season when it is lost instead of being used by crops. A part of 



FIG. 63. Moisture conservation methods as practiced in some sections of the arid 

 regions. Winter wheat continuous cropping on right, alternate crop and fallow on left. 

 Note the comparative yields. (U. S. D. A.) 



the rainfall may be saved over till the growing season by fall 

 plowing, as shown in figure 64. It is more important to know the 

 amount of rainfall during the growing season than to know the 

 total annual rainfall, but even here we may be misled by the 

 figures, as much of the rain which comes during the early spring 

 or summer may be lost in streams or by percolation through loose, 

 open soils. 



Three Conditions of Soil Water. The water which soils con- 

 tain may be: (1) free water, (2) capillary or heavy film water, 

 (3) hygroscopic or fine film moisture. 



Free water is that which can be plainly seen as water when 

 the soil is handled, or when openings are made as for post holes or 

 wells. When the soil is saturated with such water, field crops 



