CAPILLARY WATER IN THE SOIL 109 



is thoroughly distributed througliout the soil. For 

 instance, in sandy soils, the downward descent of 

 water is very rapid ; in clay soils, where the prepon- 

 derance of fine particles makes minute soil pores, there 

 is considerable hindrance to the descent of water, 

 and it maj^ take weeks or months for equilibrium 

 to be established. It is believed that in a dry-farm 

 district, where the major part of the precipitation 

 comes during winter, the early spi-ingtime, before 

 the spring rains come, is the best time for determin- 

 ing the maximum water capacity of a soil. At that 

 season the water-dissipating influences, such as sun- 

 shine and high temperature, are at a minimum, and 

 a sufficient time has elapsed to permit the rains of 

 fall and winter to distribute themselves uniformly 

 throughout the soil. In districts of high summer 

 precipitation, the late fall after a fallow season will 

 probably be the best tinre for the determination of 

 the field-water cajjacity (Fig. 29). 



Experiments on this subject have been conducted 

 at the Utah Station. As a result of several thousand 

 trials it was found that, in the spring, a uniform, 

 sandy loam soil of true arid properties contained, 

 from year to year, an average of nearly 16^ per cent 

 of water to a depth of 8 feet. This appeared to 

 be practically the maximum water capacity of that 

 soil under field conditions, and it may be called the 

 field capacity of that soil for capillary water. Other 

 experiments on dry-farms showed the field capacity 



