Dry Farming In Colorado 
13 
the minimum capillary or film condition already mentioned. In 
such condition the soil water does not move unless more water is 
added or the temperature changes so as to alter the soil water 
relation. 
Loss of Water by Evaporation .—Experiments were made in 
California to determine the water loss by evaporation. The ex¬ 
periments were run from June to September. The average evap¬ 
oration from a free water surface was about 2.88 inches per week. 
The evaporation from a saturated soil surface was 4.88 inches per 
week. When the moisture in the surface soil was about 11 per¬ 
cent the evaporation was less than 1 inch per week. When the 
percentage of water in the surface soil was slightly above 4 per 
cent the loss by evaporation was less than 0.25 inch per week. In 
other words, a dry surface soil prevents surface evaporation. 
Most dry land soils do not lose their moisture by evaporation. 
The moisture is lost by plants which use up the soil water in 
growing. In order to conserve soil water, plants must be kept 
from growing while it is being conserved. 
Advantage has been taken of the soil properties which have 
just been mentioned to store up the water falling one season to 
be used the next, by summer tillage or summer fallowing. If the 
land is cultivated one season to keep down weeds, to keep a dry 
surface and to put the soil in better shape to catch rainfall, a 
large part of the precipitation of the season can be caught and 
saved to be used the next season. Just how much can be caught 
and saved depends on how the precipitation comes. When the 
precipitation falls in quarter-inch or half-inch rains, very little 
can be saved because most of it will be lost when the dry sur¬ 
face is produced. Very heavy, dashing rains run off faster than 
they can soak in, even when the soil is in the best of shape to take 
in moisture. More water can be saved from a heavy slow rain or 
drizzle than from any other kind of precipitation. On the aver¬ 
age, on good normal soils, it will be possible to store from 50 to 70 
percent of a season’s rain to be used the next. Thus, if the nor¬ 
mal rainfall is 15 inches, the clean summer fallow will make from 
20 inches to 22 or 23 inches of water available for the use of the 
growing crop, as a portion of the rainfall of the previous season 
is stored for use in the present season. The clean summer fallow 
greatly increases the certainty of getting crops. 
It has been found by experiment, and proved by experience 
on many farms, that it is possible to get practically all the bene¬ 
fits of a clean summer fallow and at the same time raise some crop 
on the land. The crop, of course, must be a cultivated crop. Pinto 
beans, corn, grain or forage sorghums may be used as a crop. When 
