The Sauk Centre herald. (Sauk Centre, Stearns County, Minn.) 1886-current, 1898-03-24
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VALUE OF EARTH MULCH.

NHIOC VI CNnbb' "0-
Theory and Practice In Conserving the
Moisture In the Soil. ),
A writer in The Kansas Farmer, dis
cussing the value of the "eartb mulchs
and how it conserves soil moisture, says:
There are two important factors IN the
movement of soil water after drainage
has ceased-one, the thickness OF the
water films spread over the soil grains:
the other, their continuity. The exposed
surfaces in cubic foot of clay loan soil
should, if laid out fiat, cover nearly an
acre of ground. A fine division and uni
form arrangement of the soil PARTICLES
increase the amount of surface. and
hence the quantity of water each foot
will retain. If broad rubber band is
slipped over marble and pulled with
a gentle pressure, the marble will rep
resent the soil grain and the rubber
band the dlm Of moisture adhering to
it. Stretch the rubber band to the full
est limit, it's thickness is diminished, its
tension increased. AS the pull Oh the
rubber band is sfackened it becomes
thicker and is finally restored to its nor
NAL condition. When the rubber band
is thickest, it has the least grip Oh the
marble; as it becomes thinner by
stretching; its tension or grip OH the
marble is increased.
In a similar way the water adheres
to the soil grains with the least force
when the film is thickest and the sur
face exposed to the air is least, and with
greatest force when the film is thinnest
and the surface exposed to the air Is
greatest. When the film is thinnest, its
strain or tension is greatest, and it is
this strain or force that moves the wa
ter from the point in the soil where the
films are thickest to the point in the
soil where these are thinnest, till the
differences are adjusted. This move
ment has limitation not yet clearly
determined.
Let US apply this rubber band illus
tration to the conditions of the soil.
The rain has fallen and spread itself
over the soil grains to depth of two
feet, which we shall assume to be half
saturated. Drainage has ceased, and
there is no further loss downward.
Sun, wind and air promptly attack the
moisture Oh the top soil grains, the
films of water on these are thinned by
evaporation, increasing the tension,
which acts to draw water from the
grains next below, to adjust the differ
ence, and thus a stream of water is set
in motion from all parts of the soil to a
depth of two feet toward the surface
Probably half our summer rains escape
from undisturbed soils in this way and
within one week from the time of fall
right time after the shower lOosens the
surface soil, breaks the continuity of
the films, let's the air in freely to dry
out to the depth stirred and establishes
a new moisture line two to three inches
below. The water cannot reach the sur
face again. There are no moist films to
give it helping hand.
1t matters not how finely the dry sur
face soil is pulverized or how closely it
is packed, so long as the soil below is
less than half saturated water will not
rise into it, but it will rise into a very
much looser soil if it is only little
less moist. 1t is possible thas there may
be times and conditions where there is
a wider variation between the day and
night temperature which would cause
the moisture, when close to its maxi
mum during the day, to spread into the
dry soil during the night, but the COM
binations that would make this possible
are limited and exceptional.
AS the result of our Investigations
and experiments we have reached the
conclusion that the virtue in the ''earth
mulch" is i'll it's dryness, not its loose
ness, and that in maintaining the most
effective soil mulch we should aim to
keep the surface dry rather than loose.
n :.k.