104 DRY-FARMING 
Gravitational water 
It often happens that a portion of the water in 
the soil is under the immediate influence of gravita- 
tion. For instance, a stone 
= 
ie alle UE cil 
Fic. 28. Water moving downward in 
small tubes gradually becomes dis- 
tributed over the walls of the tubes as 
a capillary film. 
which, normally, is 
covered with hygro- 
scopic water is 
dipped into water. 
The hygroscopic 
water is not thereby 
affected, but as the 
stone is drawn out 
of the water a good 
part of the water 
runs off. This is 
gravitational water. 
That is, the gravita- 
tional water of soils 
is that portion of the 
soil-water which, 
filling the soil pores, 
flows downward 
through the soil 
under the influence 
of gravity. When 
the soil pores are completely filled, the maximum 
amount of gravitational water is found there. In or- 
dinary dry-farm soils this total water capacity is be- 
tween 35 and 40 per cent of the dry weight of soil. 
