STORING RAINFALL IN THE SOIL 119 



area, where the summer rains tempt the farmer to 

 give less attention to the soil-moisture problem than 

 in the dry districts with winter precipitation, farther 

 West, it is important that a fallow season be occa- 

 sionally given the land to prevent the store of soil 

 moisture from becoming dangerously low. 



To ivhat extent is the rainfall stored in soils ? 



What proportion of the actual amount of water 

 falling upon the soil can be stored in the soil and 

 carried over from season to season? This question 

 naturally arises in view of the conclusion that water 

 penetrates the soil to considerable depths. There 

 is comparatively little available information with 

 which to answer this question, because the great 

 majority of students of soil moisture have concerned 

 themselves wholly with the upper two, three, or four 

 feet of soil. The results of such investigations are 

 practically useless in answering this question. In 

 humid regions it may be very satisfactory to confine 

 soil-moisture investigations to the upper few feet; 

 but in arid regions, where dry-farming is a living 

 question, such a method leads to erroneous or in- 

 complete conclusions. 



Since the average field capacity of soils for water 

 is about 2.5 inches per foot, it follows that it is pos- 

 sible to store 2.5 inches of water in 10 feet of soil. 

 This is from two to one and a half times one year's 



