The oldest direct comparison between these two systems
of farming, so far as the writer has learned, is on
the experiment fields of the University of Illinois,
where as an average of six years the yield of corn
has been 87 bushels an acre in grain farming and 90
bushels in live-stock farming, the same crop rotation
being practiced. Where wheat was introduced the
average yield for six years was 43.1 bushels in grain
farming and 43.5 in live-stock farming.
No nitrogen was purchased in any form in either of
these systems; but clover is grown in the rotation
to secure nitrogen from the air and then the crop
residues or farm manure is returned to the soil to
provide sufficient nitrogen for the grain crops.
In all cases phosphorus was used for these yields.
Even more encouraging than these six-year average
results from Illinois are the results of sixty years
from Agdell Field at Rothamsted.
Where mineral plant food was regularly applied, and
where all the manure produced by feeding the turnips
was returned to the soil, in a four-year rotation
of turnips, barley, clover (or beans) and wheat, with
no other provision made for supplying nitrogen, the
yields per acre were as follows:
Turnips, 24,724 lbs. in 1848, and 26,410 in 1908.
Barley, 42.8 bushels in 1849 and 22.1 in 1909
Clover, 5586 pounds in 1850 and 7190 in 1910.
Wheat, 32 bushels in 1851 and 37.8 in 1911.
Here we have data which span a period of sixty years
and which show that where mineral plant food has been
provided the clover in rotation and the manure produced
by the feeding of only one of the four crops have
maintained the yield of all crops except the barley-the
third crop after clover-and without the application
of nitrogen in any other form. If the clover
and straw had been returned to the land either directly
or in farm manure the additional nitrogen thus provided
would have been sufficient both to maintain the yield
of barley and to prevent the moderate decrease which
has occurred in the nitrogen content of the soil.
PHOSPHORUS: THE MASTER KEY
The greatest economic loss that America has ever sustained
has been the loss of energy and profit in farming
with an inadequate supply of phosphorus. Phosphorus
is a Greek word which signifies “light-bringer”;
but it is a light which few Americans have yet seen,
else we should not permit the annual exportation of
more than a million tons of our best phosphate rock,
for which we receive at the mines the paltry sum of
five million dollars, carrying away from the United
States an amount of the one element of plant food we
shall always need to buy, which if retained in this
country and applied to our own soils would be worth
not five million but a thousand million dollars for
the production of food for the oncoming generations
of Americans.
