108 DRY-FARMING 
the soil grains is very minute. King has calculated 
that a film 275 millionths of an inch thick, clinging 
around the soil particles, is equivalent to 14.24 per 
cent of water in a heavy clay; 7.2 per cent in a loam; 
5.21 per cent in a sandy loam;.and 1.41 per cent in 
a sandy soil. 
It is important to know the largest amount of 
water that soils can hold in a capillary condition, 
for upon it depend, in a measure, the possibilities 
of crop production under dry-farming conditions. 
King states that the largest amount of capillary 
water that can be held in sandy loams varies from 
17.65 per cent to 10.67 per cent; in clay loams from 
22.67 per cent to 18.16 per cent, and in humus soils 
(which are practically unknown in dry-farm sections) 
from 44.72 per cent to 21.29 per cent. These results 
were not obtained under dry-farm conditions and 
must be confirmed by investigations of arid soils. 
The water that falls upon dry-farms is very 
seldom sufficient in quantity to reach the standing 
water-table, and it is necessary, therefore, to deter- 
mine the largest percentage of water that a soil 
can hold under the influence of gravity down to a 
depth of 8 or 10 feet — the depth to which the roots 
penetrate and in which root action is distinctly felt. 
This is somewhat difficult to determine because the 
many conflicting factors acting upon the soil-water 
are seldom in equilibrium. Moreover, a consider- 
able time must usually elapse before the rain-water 
