The Raymer enterprise., 1911-10-26
ESCAPE OF MOISTURE
Conditions Of the Evaporation of
Water From Soil.
Under Ordinary Conditions Il Is I'm.
possible to Remove All Liquid Mat.
:. ter, for Small Quantity 10
Strongly Attracted.

Evaporation does not alone occur
from the surface of free water. All
wet or moist substances lose by evap-
Grafton most Of the water that they
hold. providing the conditions Of tenn
perature and relative humidity are IA
yorable. Thus. from a wet soil. evap-
oration is continually removing wa
ter. Yet. under ordinary conditions.
1t is impossible to remove all the
water. for small quantity is attract
ed SO strongly by the soil particles
that only temperature above the
boiling point Of water will drive 1t
out This part OF the soil is the
microscopic moisture.
Moreover, 1t must be kept In mind
that evaporation does not occur as
rapidly from wet soil as from a water
surface, unless all the soil pores are
20 completely filled with water that
the soil surface is practically water
surface. The reason for this reduced
evaporation from wet soil Is almost
eell-evident. There is comparative.
ly strong attraction between the soil
and water, which enables the moist.
ure to cling as thin capillary film
around the soil particles, against the
force of gravity. Ordinarily only cap
Hilary water is found in well-tilled
soil, and the force causing evapora.
tion must be strong enough to over
come this attraction besides chang.
ing the water into vapor.
The less water there is In the soil.
the thinner the water film, and the
more firmly is the water held. Hence,
the rate Of evaporation decreases
with the decrease OF soil moisture.
This law is confirmed by actual field
tests. For instance, in an average
Of 274 trials made at the Utah sta.
ton. 1t was found that three soils.
otherwise alike. that contained respec-
lively. 22.63 per cent, 17.14 per cent.
and 1875 per cent. Of water lost in
two weeks to depth Of eight feet.
respectively. 21.0, Ill. and 100 pounds
Of water per square foot. Similar
experiments conducted elsewhere also
furnish proof Of the correctness of
this principle. From this point Of
view the dry farmer does not want
his soils to be unnecessarily moist.
The dry farmer can reduce the per
cent. OF water In the soil without di.
minishing the total amount Of water
by so treating the soil that the water
will distribute Itself to considerable
depths. This brings into prominence
again the practice Of fall plowing.
deep plowing. sub.soiling. and the
choice Of deep soils for dry farming.
Very much for the. same reasons.
evaporation goes on more slowly from
water In which salt or other sub
stances have been dissolved. The at.
traction between the water and the
dissolved salt seems to be strong
enough to resist partially the force
causing evaporation. Soil water al.
ways contains some Of the soil ingre.
dents In solution. and consequently
under the given conditions. evapora.
tion occurs more slowly from soil
water. Now, the more fertile the
soil Is. that is. the more soluble
plant food 1t contains. the more ma
terial will be dissolved in the soil
water. and as result the more slow.
ly will evaporation take place. Fol.
lowing, cultivation. thorough plowlng
and manurirg, which increase the
store Of soluble plant food. all tend
to diminish evaporation. While these
conditions may have little value In
the eyes Of the farmer who is under
an abundant rainfall. they are of
great Importance TO the dry farmer.
II Is only by utilizing every posi-.
bility OF conserving water and fer
tility that dry farming may be made a
perfectly safe practice.