158 THE PRINCIPLES OF SOIL MANAGEMENT 



foot would be 88, 79 and 58 pounds each. Using the 

 maximum and minimum moisture contents indicated 

 by the above curves, the available moisture retained 

 by each of the soils is as follows: 



Table XXIV 



It is possible that the maximum assumed for the clay 

 is too high, in which event the available moisture in 

 the fifth column for this soil is also too high; but field 

 experience indicates that it is reasonable. 



By reference to page 134, giving the amount of water 

 required to produce a crop, it will be observed that the 

 surface four feet of the sand soil will not retain enough 

 water for the medium crop yield, and that the clay 

 soil contains less than half enough water for a large 

 yield of many crops under the best management. This 

 necessitates the replenishment of the supply by rainfall, 

 irrigation, or movement up from the subsoil, after the 

 best tillage practice has been employed to prevent 

 unnecessary loss by evaporation. 



77. Relation of surface tension to capillarity. In 

 addition to the three factors mentioned as controlling 



Assumed. 



