224 Irrigation and Drainage 



of desiccation of the soil which the particular crop 

 will tolerate before serious interference to growth re- 

 sults. 



THE CAPACITY OF SOILS TO STORE 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: 



Loss .95 .64 .4 3.39 .08 5.81 2.94 



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 



