CHAPTER XXI 



APPLYING WATER FOR IRRIGATION 



Principles Involved. In applying irrigation water, con- 

 sideration should be given to some of the principles govern- 

 ing the wetting, puddling, and washing of the soil. If these 

 points are not studied in connection with each type of soil, 

 much more water may be used than necessary, and it 

 may be used in a way harmful to the crops. A good 

 irrigation farmer observes closely the effects of the appli- 

 cations on the soil and plant, and continually endeavors 

 to improve his methods. When water is applied to the 

 surface, it starts to percolate downward and outward. If 

 the soil be coarse, the water will travel almost directly down- 

 ward, especially if the texture becomes more open or coarser 

 as the depth increases. It is then necessary to apply the 

 water to the entire surface to get the best results. When 

 water is applied to a fine loam underlaid by a subsoil of very 

 fine texture, the water percolates downward slowly by grav- 

 ity and spreads laterally by capillarity. For this reason the 

 water may effectively be applied to these soils in furrows 

 some distance apart. 



When the soil is very dry, the percolation downward is 

 less rapid than when it is more moist. This is accounted for 

 by the fact that the air in the soil must be displaced before 

 the water can travel downward. This takes time, and for 

 this reason a soil will not take water as rapidly when dry as 

 when moist. 



In applying irrigation water, great care should be taken 

 not to puddle the soil, that is, to cause the crumb structure to 



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