184 



THE PRINCIPLES OF SOIL MANAGEMENT 



The following curves show the capillary transfer of 

 water in two soils through eight feet horizontally. 



18 



12 



10 



* 4 



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DISTANCE FROM EXPOSED END, IN FEET 



Fig. 58. Curves showing the initial moisture content of horizontal columns 

 of sand and clay loam soil and the distribution of moisture after free evapora- 

 tion from one end of each column, for a period of days. Note the general 

 movement of water throughout the columns. 



It is evident that plants may make use of supplies 

 of moisture to one side, as well as below their roots even, 

 in some soils, to a distance of several feet, through the 

 agency of capillarity. On the other hand, irrigation 

 farmers have repeatedly noted the very limited lateral 

 influence upon crops of the application of water in irri- 

 gation. The limit of the application of water is in some 

 soils marked almost to the row. In this instance, it 

 should be remembered that water is added only after 

 the soil has become relatively dry, at which stage the 

 moisture films move with great difficulty due to friction, 

 and probably also to cracks, which of course very effect- 

 ively break up capillarity. King has concluded from 

 studies on vertical columns that an adjustment of water 

 through ten feet of soil may readily take place. 



