144 DRY-FARMING 



distribution of water under such conditions is seen 

 in the table on page 1 14 of the last chapter. During 

 the greater part of the year, however, no such quies- 

 cent state can occur, for there are numerous dis- 

 turbing elements that normally are active, among 

 which the three most effective are (1) the addition 

 of water to the soil by rains ; (2) the evaporation of 

 water from the topsoil, due to the more active meteor- 

 ological factors during spring, summer, and fall ; and 

 (3) the abstraction of water from the soil by plant 

 roots. 



Water, entering the soil, moves downward under 

 the influence of gravity as gravitational water, until 

 under the attractive influence of the soil it has been 

 converted into capillary water and adheres to the 

 soil particles as a film. If the soil were dry, and the 

 film therefore thin, the rain water would move down- 

 ward only a short distance as gravitational water; 

 if the soil were wet, and the film therefore thick, 

 the water would move down to a greater distance 

 before being exhausted. If, as is often the case in 

 humid districts, the soil is saturated, that is, the 

 film is as thick as the particles can hold, the water 

 would pass right through the soil and connect with 

 the standing water below. This, of course, is sel- 

 dom the case in dry-farm districts. In any soil, 

 excepting one already saturated, the addition of 

 water will produce a thickening of the soil-water 

 film to the full descent of the water. This imme- 



