SOIL AS WATER RESERVOIR 35 



29. Soil treatment. A deep, continuous soil is the 

 best under irrigated conditions. On such a soil enough 

 water may be added at each irrigation to leave the top 

 foot saturated after distribution has occurred. This 

 quantity varies usually from a depth of 5 to 8 inches over 

 the whole area. To make more rapid the entrance of 

 water into the soil, the surface should be kept in a loose, 

 absorptive condition. The deeper the soil is plowed, the 

 greater the quantity of water that may be stored in a 

 given time, in the top soil, to move gradually downward 

 into the subsoil. Since the application of water tends to 

 compact the soil, it becomes necessary to stir the soil 

 between irrigations. Such stirring not only makes it 

 easier for water to enter the soil; it also reduces the loss 

 from evaporation. 



Soils, which within 10 or 12 feet from the surface are 

 underlaid with hardpan or ground water, or made dis- 

 continuous by gravel streaks or layers, must be irrigated 

 cautiously. In such cases the quantity of water to be 

 added should be such as to allow only a thin soil-mois- 

 ture film to reach the hardpan, ground water or gravel. 

 Small, frequent irrigations must be the^rule in such cases 

 smaller and more frequent as the faults are nearer 

 the surface. 



30. How much water can be stored. It is clear from 

 the statements of this chapter that water may be stored 

 in soils to considerable depths as a film surrounding the 

 soil particles and filling the capillary spaces. Since water, 

 whether from rain or irrigation, is ordinarily applied 

 intermittently, it is important to know how much of the 

 water added at any one time is retained by soils for 

 the use of plants. 



At the Utah Station, where most of the precipitation 



