Pullman herald. [volume] (Pullman, W.T. [Wash.]) 1888-1989, 1912-07-19
Lecture on Soils
y, professor R. w. Ihatcher)

.onortions of sand, clay and decay
10 vegetation or "humus. If
.,,sd in proper proportion to form
~ easily titled soil, this is called
'n.om" The so-called volcanic"
- 81 not the ashes from a volcano,
~, simply fine loan derived from
srs of volcanic origin. 1t is COM
NON all over Eastern Washington.
.oThe two chief factors in deter
aiming the productivity of soil are
,,s water-holding capacity and its
tore of available plant food. 1t is
-. the amount of water which goes
,,,o the soil in the form of rain or
,rrigation water that limits crop
.owth but the amount that stays
,hora until the crops need 1t.
The water-holding capacity of the
soil depends chiefly on its humus
content and on the fineness of the
ooi, particles. BY experiment, it was
shown that pure humus holds 25
times as much water when it is wet
enough for tillage as does pure sand
uuch of this extra water is avail
ohle for crop growth. A sandy soil
will allow most of the water which
ia anplied to it to run down through
II and be lost, but the addition of
humus to it tends to prevent the loss
Water moves upward and side
wise through the soil by capillary ac-
tion, 1t will come up from a dis
lance varying from three feet in a
very sandy soil to six or seven feet in
fine clay. A fine-grained soil with
nenty of humus Will hold more
water. and raise it further by capil-
larity than any other type. Hence,
good humus supply in this fine val
lev loan is the chief requisite for the
best use of soil water The mineral
mart of the loan soil of this valley
is most excellent for water-holding
capacity, but it's humus supply is
rather low. Humus in the soil is de-
stroyed rapidly by clean cultivation.
But clean cultivation is valuable and
practically necessary to preserve the
mulch which prevents losses of soil
moisture by evaporation. Fall and
spring growing of cover crops to be
plowed under to add humus to the
soil is a most excellent practice
Three inches of loose earth is the
most effective mulch. 1t ought not
to be too fine. hence too frequent
stirring is not desirable. Surface
tlllage should be just often enough
to keep the mulch loose. Cultiva-
ton should be at different depths at
different seasons of the year, in
order to prevent the formation of
underground or 'plowsole Orchard
soils ought to be plowed once year
as deeply as can be done without cut
ting off too many tree roots. Then
summer cultivation should be shall
low in order to leave as much of the
soil as possible in shape for the
growth of the feeding roots of the
trees.
There are four elements in the soil
which have special uses as plant
food, Nitrogen makes foliage
ueaVes and young stems, etc. 9.
fhosphorous goes chiefly to the pro-
duction of seeds. Potassium is used
IN the manufacture of starch and
sugars, hence in the growth of
fruits, tubers, etc. Calcium (lime)
is used for the development of woody
nDre These elements are necessary
70 all crops, but in different proper
lions for the different kinds of crops
All agricultural soils contain suf-
hclent total supplies of these ele-
ments to last for hundreds of years;
oa' the amount which can be used
" crop in any one year, and the
leSuieing crop growth, depends upon
mueu Is In available form. To
We available as plant food, the ma
'erial must be in form that can be
uiSSoiVed in soil water and so pass
~ through the plant roots and circu-
la'e IN the sap. Only that part of
'ue SOIL which is thus soluble can by
'Ae com oined action of moisture, air
anu the acids which are produced by
a'Osylng vegetation (humus). Hence
sufficient humus supply and a good
oi tilth, permitting free circu-
.aion OF air and moisture are neces-
ar 10y 10 render the plant food of the
soil available.
=,