The independent-reporter., 1913-06-19
CROPS DERIVE FOOD
FROM SOIL
Roots of Plants Take an Active Part
In DissOlying Plant Food

since crops derive SO large pro-
portion of their food from the soil,
it is quite natural that We should
come to think of the chemical COM
position of the soil as the correct
measure of its fertility. The uni
versity is frequently asked to make
soil analyses, and for some reason re-
quests of this nature have been un-
usually numerous during the present
spring. In many instances samples
of soil are forwarded, and specific In
formation is asked for. the writer
stating perhaps that he grew potatoes
last season, and wishes to SOW oats
this spring. The analysis in such cases
is supposed to be trustworthy guide
in the selection of a fertilizer. In
other cases the writer merely states
that the soil in question failed to give
good returns last season, and he looks
for an analysis to suggest a remedy.
A great many soil analyses have
been made, and the published results
deserve close study. One of the
most interesting facts which such in
vestigations have brought to light is
that nearly every soil, even those in
capable of producing good crops, con-
tain a store of plant food far in eX
cess of the needs of the very crops
they fail to produce. A plant is able
to take its food from the soil only in
soluble forms, while by far the great
er part or tle elements needed by
crops exist in the soil in the form of
insoluble compounds, which are con-
seouently not available. A chemical |
ANALYSIS simply shows that they are
there. Up to the present time the |
chemist has not devised reliable |
method by which he can measure the
availability of these materials to the |
plant. Even if he succeeded in de
termiuing the availability for a cer /
tain crop he would have made but
little progress, since he might find it |
necessary to establish a different
standard for every crop. The roots
of plants take an active part in dis
solving plant food and no two kinds
of plants possess this power in the
same degree.
Tho Importance of the quality |
which we call "availabiity" may be
illustrated thus: Soils frequently |
carry over one thousand pounds OF
phosphoric acid in the upper six or
seven inches of an acre. yet fail to |
produce good crops for want Of this
very compound. Supposing now, we
add to such soil a fertilizer carry |
ing 10 per cent available phosphoric
acid, applying it at the rate Of one
thousand pounds to the acre, and
working 1t into the soil to the depth
of seven inches. The half ton of
fertilizer carries one hundred pounds
OF available phosphoric acid, which
has become mixed with two million
pounds OF earth. A little calculation
will show that we have added phos-
phoric acid to the extent of one-half
of one hundredth of one per cent If
such a soil were analyzed before and
after such an application, an ordinary
chemical analysis would not detect
the difference. Yet in spite of the
fact that the soil may have already
contained ten or twenty times this
amount. the crop knows the diff
ference.
There is but one way to learn tho
fertilizer requirements of the soil,
and that is by close observation and
careful experimentation on the part
of the man who tills the soil II
the application of potash salts alone
produce satisfactory results, nitrogen
and phosphoric acid should not be
used. The indiscriminate use of a
complete fertilizer" is fairly certain
to increase the crop but the practice
Is in many cases a wasteful one. The
University holds itself ready to aid
the farmer in every way within its
power, but for the reason stated it
cannot undertake soil analyses.
L. H. MERRILL,
Prof. of Agricultural Chemistry.