The Brookings register. [volume] (Brookings, Brookings County, S.D.) 1903-1971, 1909-12-16
SOIL EXPERT

report on Investigations he made or
the relation of soil water to- produc-
tiyity in South Dakota and Washing
ton. DR.. MCGEE is an expert on soil
erosion and his report should prove
interesting. In part he says:
"In central South Dakota the rain
fall averages little more than 10 in
ches: yet the subsoil and the Creta-
cious shales below are moist TO a de-
gree evidently greater than can be
ascribed to that precipitation. The
region is artesian, flowing wells DC
curing wherever the shales are drill
ed through to the Dakota sandstone
hundreds or thousands Of feet below,
TIE sandstone o~ut-cropping in the root
mills of the Rock Mountains, and in
cIining eastward beneath the younger
shales. While the shales from the
combining stratum or cover FOR the
sandstone, they are more or less pre-
yious; and under the hydrostatic
head Of hundreds of thousands of feet,
a part of the water escapes upward
to exude slowly at the surface, and
e%vaporates either directly or through
the action of growing plants. While
the quantity Of water supplied by this
natural sub-irrigation system has not
beer measured, 1t Is estimated at an
inch per inch per month or n loot per
year which with the Is inches of rain
fall suffices for moderate productivity.
The conditions extend beyond South
Dakota throughout "A considerable
portion of the great plains, affecting
an area OF several million acres. This
Is a region of successful dust mulch
ing Tor dry farming); for the dust
LAYER at the surface o only retains
much OF the moisture derived from
the rainfall but conseryes the subter-
ranean supply for the use of the crops.
Thus the seasons work shows that the
productivity and Availability of the
great plains are greatly Increased by
a natural s~ub-irrigation which renders
available for agriculture not only the
local precipitation but a part OF the
rain descending on a nearl. equal
area of broken country extending
westward into the mountains.
In eastern Washington and ada
cent parts OF Idaho there are several
classes OF land considered In relation
to water supply and productivity. The
most extensive comprises the lava
beds of the largest known area of vol
canic rock, over which the rainfall
averages little over 20 inches /. g.,
hardly enough for full productivity.
Portions of the lava are deeply com
posed, yielding a p~ulverulent and fri
able soil and subsoil well adapted to
retaining water from either rains or
irrigation; these form the far-famed
wheat lands In which dust-mulching
is advantageous and the product abun-
dant every year OF n In two or three
years according to the water supply.
Elsewhere the lavas are decomposed
to less depths. and here a consider
able part of the rainfall Is lost by
percolation through the porous and
cavernous rocks, perhaps to reap
pear as springs and seepage in the
valleys; and the productivity is limit
ed and uncertain.
Another class of lands Is that OF
the mountains and foothills. usually
wooded and too broken for agricul-
ture; they form catchment areas for
streams, which are notably clear and
uniform throughout the year so long
as the forests remain, but become
turpid and ~torrential with deforesta-
ton.
A third class of land occurs in val
leys. usually lined with gravel through
which water percolates freely. When
the ground water reaches the surface,
forests OF cedar and hemlock abound,
and when the land is cleared drainage
ia required; when the water-table is
q few feet lower the surface Is wood
ed with upland trees, and when clear
ed the soil Is highly productive; and
when the watertable lies at a depth
the lands are useless and virtually
unproductive without irrigation
though In some cases las in Spokane
Valley the underflow is so abundant
as I O sustain irrigation by pumping
with high productivity.
The three classes of lands illustrate
the varying efficiency of soils, yet
demonstrate the direct dependei ce
of productivity on the water supply.
Much Of western Washington hears
remarkably exuberant forests and IN
firs 200 to 800 feet in height, sustained
by ample though variable winter rains.
The coverlet of lofty trees, the blank
A-~ho ohoya anA ~f hrOadla1f