Dry Farming In Colorado 
ii 
spaces does not exist for any length of time. The water is all held 
as thin films around soil particles. These are stretched as thin as 
they can be by soil attraction, because there is always dry soil be¬ 
low trying to pull it away from the moister soil above. The con¬ 
dition is a balanced one, one portion of the soil trying to pull the 
water away and the other resisting with equal strength. This con¬ 
dition we call the minimum capillary or film capacity. In a 
sandy soil this minimum film capacity varies somewhat, but is 
from 7 percent to 11 percent. This percentage of water ranges 
from 0.84 inch to 1.32 inch per foot of soil. In a silty soil the per¬ 
centage is higher, ranging around 12 percent to 18 percent, de¬ 
pending on the proportion of silt in the soil. This equals from 
In dry years, Russian Thistles may help out the feed supply, if harvested 
at the proper time 
1.44 inches to 2.16 inches of water per foot of soil. In a clay or 
adobe soil the percentage of minimum film water amounts to 18 to 
25 percent and even more where the percentage of clay or adobe 
is very high in the soil. The percentages equal from 2.16 inches 
to 3 inches of water per foot of soil. Thus it is seen that heavy 
soils, as silt and clay, retain more water per foot than light sandy 
soils. 
Available Water .—But all the water a soil contains is not 
available for the growth of plants. Plants can only take out a 
portion. Some plants can take out more than others. For in¬ 
stance, sorghum will dry out a soil more than wheat. Wheat will 
take away more water than corn. Russian thistles and sunflowers 
will dry out a soil worse than any of those crops which we try 
to grow for profit. Most crops will dry out a sandy soil so that 
only 2 to 4 percent of the moisture remains. 
