224 Irrigation and Drainage 



of desiccation of the soil which the particular crop 

 will tolerate before serious interference to growth le- 



sults. 



THE CAPACITY OF SOILS TO STOEE WATER 

 UNDER FIELD CONDITIONS 



The amount of water which may be stored in soils under- 

 field conditions varies between wide limits with the character 

 and texture of the soils, and also with the distance of standing 

 water in the ground below the surface. 



When a fine sand will hold in the first foot above the 

 ground -water 23.86 per cent of its dry weight of water, at 4 feet 

 above it was found to hold only 8.12 per cent, and 8 feet above 

 only 3.14 per cent of the dry weight. When these amounts are 

 expressed in pounds per cubic foot, they stand only a little more 

 than 23.86 pounds, 8.12 pounds, and 3.14 pounds, a cubic foot 

 of the dry sand weighing about 105 pounds. 



In the case of a natural field soil of sandy clay loam with 

 clay subsoil changing to a sand at 4 feet, and where the 

 ground-water changed during the season from 7.6 feet below 

 the surface to 8.4 feet, the water content of the soil was found 

 to be as follows: 



1st ft. 2d ft. 3d ft. 4th ft. 5th ft. 6th ft. 7th ft. 



During this interval there had been a rainfall of 10.84 

 pounds per square foot. There is no doubt that in the upper 

 4 feet a considerable part of the water was lost through surface 

 evaporation. It is quite likely, also, that a portion of the loss 

 shown in the 5th, 6th, and 7th feet was due to an upward capil- 

 lary movement. But there is little reason to doubt that the 



