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 what 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 25 inches of water in 10 feet of soil. 
This is from two to one and a half times one year’s 
