RELATION" OF SOILS TO IRRIGATION. 27 



scientific application of fertilizers, the growing of nitrog- 

 enous plants, or by crop rotation. 



Capillary Action. In concluding our observa- 

 tions on this important topic of soils the matter of cul- 

 tivation must not be overlooked. The success of irriga- 

 tion cannot be made complete without cultivation, and 

 it is a fault too commonly observed among irrigators 

 that they are inclined to depend too much upon irriga- 

 tion and not nearly enough upon cultivation. The re- 

 tention of the moisture when once supplied to the soil 

 by moans of irrigation may be largely controlled by 

 keeping the topsoil well pulverized so as to break up 

 the capillary tubes, as shown in Figure 5, a being the 

 surface, t> the capillary tubes, and c the subsoil. The 



FIG. 5. CAPILLARY TUBES OF SOIL. 



more recent scientists all agree that the soil is full of 

 small tubes, through which the moisture from below 

 finds its way to the surface and escapes. If these tubes 

 can be closed the water will not evaporate so readily. 

 This is done by loosening the topsoil, not by stirring 

 it to such a depth as to injure the roots of the plant, 

 but in a manner so as to break the tops of the tubes 

 and throw a covering of loose soil over the ground, 

 and at the same time destroy the robber weeds which 

 not only use the moisture but take away plant food as 

 well. This loose soil is a mulch a blanket which pre- 

 vents loss of moisture and protects against the direct 

 rays of the sun. There are of course certain kinds of 

 cereal crops, such as wheat and oats, which by ordinary 



