PHOSPHORUS: THE MASTER KEY TO PERMANENT AGRICULTURE
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.
For five million dollars we export to Europe each year enough
phosphorus for 1,400,000,000 bushels of wheat, or twice the average
crop of the entire United States. Meanwhile our ten-year-average
yield of wheat is 14 bushels an acre, while Germany's yield has gone
up to 29, Great Britain's to 33, England's to 37-1/2 and Denmark's
to more than 40 as the average for a decade.
Potato Yield Twice Doubled
There is only one place in the world where we can go for the results
of soil improvement for more than a quarter of a century in
connection with the growing of potatoes. Of course this place is
Rothamsted, England, where as an average for twenty-six years the
yield of potatoes was 51 bushels an acre on unfertilized land and
exactly 102 bushels where only a phosphate fertilizer was applied.
Where the same amount of phosphorus--29 pounds of the element per
acre per annum--was used in connection with other minerals--300
pounds of potassium sulfate and 100 pounds each of the sulfates of
magnesium and sodium--the average yield of potatoes was 109 bushels.
Where 86 pounds of nitrogen was applied in sodium nitrate the
average yield was 79 bushels; but where the nitrogen, phosphorus and
other minerals were all applied the average yield for the twenty-six
years was 203 bushels.
At 50 cents a bushel for potatoes, the investment in phosphorus
alone paid 600 per cent net profit; and even the complete
fertilizer, including 392 pounds of acid phosphate, 550 pounds of
sodium nitrate and 500 pounds of alkali salts, aggregating 1442
pounds, and costing at moderate prices $24.28 an acre per annum,
paid back $76 a year as a twenty-six year average, thus making 300
per cent even on an investment of nearly $25 an acre a year.
Phosphorus Helps Good Farming
There is also but one place in the world where we can learn the
results secured from the application of phosphorus for a period of
thirty-six years in a good system of farming; and again this place
is Rothamsted.
In 1848 Sir John Lawes and Sir Henry Gilbert began investigations on
Agdell Field. The Norfolk rotation, already known at that time as
one of the best rotation systems, was turnips, barley, clover, and
wheat; and in these practical field experiments the turnips were fed
on the land and the animal fertilizer thus produced was returned to
the soil, which was well supplied with limestone.
During the next thirty-six years $29.52 worth of phosphorus per acre
was applied to one part of the field; and in comparison with another
part of the same field cropped and managed similarly, except that no
phosphorus was applied, the $29.52 worth of phosphorus produced
$98.02 increase in the value of the turnips, $37.45 in barley,
$48.93 in clover (and beans) and $45.99 in wheat.
The total value of the crops grown on the land not receiving
phosphorus during the thirty-six years was $432.43 an acre, while on
the phosphated land the crop values amounted to $662.82, an increase
of $230.39 from an investment of $29.52, the turnips being figured
at $1.40 a ton, barley at 50 cents a bushel, clover hay at $6 a ton,
beans at $1.25 a bushel, wheat at 70 cents a bushel, and phosphorus
at 12 cents a pound. As a general average at these conservative
prices, the investment of $3.28 an acre every four years paid back
$25.60 in the four crops.
In most states the legal rate of interest is 6 per cent but here is
an investment that paid the principal and 680 per cent interest
every four years. And these investigations show that the phosphorus
was used with profit for the production of markedly different crops,
including potatoes and turnips, barley and wheat, clover and beans.
But the soil at Rothamsted is no poorer in phosphorus than is the
average soil of the United States; and these results are given here
not only because they are the oldest and most trustworthy the world
affords, but because they are strictly applicable to the production
of common crops on vast areas of agricultural land in our own
country.
The Form of Phosphorus to Use
The unfertilized soil at the Rothamsted station contains, in
2,000,000 pounds--corresponding to about 6-2/3 inches to the
acre--1000 pounds of phosphorus and 35,000 of potassium, while an
acre of plowed soil of the same weight at State College,
Pennsylvania, contains 1100 pounds of phosphorus and 50,700 of
potassium.
In a word, normal soils are deficient in phosphorus, and the
application of phosphorus in good systems of farming produces marked
and profitable increases in crop yields. But what form of phosphorus
shall we apply? This is a very important question in agricultural
economics, for we have many different kinds of fertilizing materials
that contain phosphorus, and one may cost ten times as much as
another as a source of phosphorus. Thus 250 pounds of phosphorus in
a ton of finely ground natural rock phosphate can be purchased at
the mines in Tennessee and delivered at the farmer's railway station
in the heart of the Corn Belt for $8. Or the ton of raw phosphate
may be mixed with a ton of sulfuric acid in the fertilizer factory,
and the two tons of acid phosphate may be sold to the same farmer
for $32. Or the fertilizer manufacturer may mix the two tons of acid
phosphate with two tons of "filler," containing a little nitrogen
and potassium, and then sell the same farmer the four tons of
so-called "complete" fertilizer for $80; and the farmer gets no more
phosphorus in the four tons of "complete" fertilizer for $80 than in
the one ton of natural phosphate for $8.
The Pennsylvania State College conducted an experiment for twelve
years--1884 to 1895--in which $1.05 an acre was invested in ground
raw rock phosphate with a rotation of corn, oats, wheat and hay
(clover and timothy), and the value of the increase produced by the
phosphorus amounted to $5.85 as an average for the twelve years, and
to $8.41 as an average for the last four years. Thus the profit was
from about 560 to 800 per cent on the investment, counting corn at
35 cents a bushel, oats at 30 cents, wheat at 70 cents, and hay at
$6 a ton. These figures represent the increase produced by
phosphorus over and above the value of the crops grown without
phosphorus fertilizer. In this case no farm manure was used on
either part of the field; but commercial nitrogen and potassium were
applied alike on both parts, and clover was grown in the rotation.
Acid phosphate was also used in direct comparison; and, in answer to
the question whether the general farmer should apply liberal amounts
of finely ground natural rock phosphate, or whether he should pay
four times as much for phosphorus after the fertilizer manufacturer
has mixed one part of the raw rock with one of sulfuric acid and
thus produced two parts of acid phosphate, these Pennsylvania
experiments tell us that the yearly average for the twelve years
gave a gain per year of $2.45 from the raw phosphate and 48 cents
from the acid phosphate, at the prices used by the Pennsylvania
Experiment Station. But we must not draw general conclusions from
this one experiment, even though it covers twelve years.
In 1895 the Maryland Experiment Station began field experiments with
different forms of phosphorus; and, as an average of six tests every
year for twelve years, $1.965 invested in ground raw rock phosphate
produced increases in corn, wheat and hay that were worth $22.11, at
35 cents a bushel for corn, 70 cents for wheat, $6 a ton for hay,
and 3 cents a pound for phosphorus in the ground natural phosphate.
How would you like 1000 per cent profit as the result of mixing
brain with brawn, in connection with the improvement of your own
business, thus keeping the investment under your own control?
Mind you, this does not prove that farming is profitable, but only
that the intelligent use of phosphorus in farming is profitable. In
other words the admixture--brains--is profitable.
In commenting upon his investigations the director of the Maryland
Agricultural Experiment Station states that the raw phosphate
produced a higher total average yield than acid phosphate, and at
less than half the cost.
The Rhode Island Experiment Station began a series of experiments
with different forms of phosphorus in 1894. If we add together all
the hay and grain crops grown during the decade following the first
year of these experiments, we find that the increases per acre were
14,580 pounds for raw phosphate and 14,550 pounds for acid
phosphate, on unlimed land; while lime and raw phosphate produced
27,030 pounds, and lime and acid phosphate 29,690 pounds, of
increase; and the acid phosphate cost three times as much as the raw
phosphate.
In commenting upon these investigations the director of the Rhode
Island Experiment Station states that the raw phosphate gave very
good results with such farm crops as oats, peas, crimson clover,
millet, soy beans, and so forth, but very poor results with such
garden crops as turnips, rutabagas, cabbage, beets, lettuce, squash,
and so forth, and its use for these garden crops is not advised.
In 1890 the Massachusetts Experiment Station began investigations
with different phosphates applied in equal money value, and in his
report for 1900 the director states that the raw rock phosphate
ranks above the acid phosphate both as an average for the entire
period and as an average between 1895 and 1900, during which time
the land to which no phosphorus was applied produced only 55 per
cent as much as where raw phosphate was used--a result worth every
farmer's consideration.
More Bushels and Tons
The Ohio Agricultural Experiment Station has reported investigations
covering sixteen years in which raw phosphate was compared with acid
phosphate costing twice as much per acre. As an average of all
results secured, 320 pounds of raw phosphate applied with manure on
clover sod produced 8.4 bushels more corn, 4.7 bushels more wheat,
and 0.49 ton more hay per acre than where manure alone was used, and
320 pounds of acid phosphate, costing twice as much money but
containing only half as much phosphorus, applied with the same
amount of manure, produced 7.5 bushels more corn, 5.1 bushels more
wheat, and 0.46 ton more hay than where the manure alone was used.
Now I have presented the averages or summaries of all investigations
that have been reported covering ten years or more where equal money
values of raw phosphate and acid phosphate have been used, or where
any apparent provision was made to supply some organic manure,
whether as farm manure, green manure or merely as clover grown in
the rotation; and I invite the reader to mix his own brains with
these data and not to expect me to state whether he should use the
relatively cheap ground natural phosphate rock or the more costly
manufactured acidulated phosphate in the improvement of his own soil
in systems of permanent profitable agriculture.
Making Phosphate Available
If the natural rock is used it should be ground so that at least 90
per cent will pass through a sieve with 10,000 meshes to the square
inch, and of course its content of phosphorus (from 12 to 15 per
cent) or of so-called "phosphoric acid" (from 27 to 34 per cent)
should also be guaranteed. Moreover it should be used liberally and
in connection with plenty of decaying organic matter. People
sometimes ask, "How much of the phosphorus in raw phosphate is
available?" The best answer to this question is, "None of it; and,
if you are not going to make it available, don't use it."
On my own farm I use about one ton per acre of raw phosphate once
every six years, thus adding at least 250 pounds of phosphorus at a
cost of less than $8; whereas 200 pounds of the common "complete"
fertilizer per acre yearly would cost $12 every six years, and would
supply only 40 pounds of phosphorus. I do not use "complete"
fertilizers, because there is plenty of nitrogen in the air and
plenty of potassium in the soil; and because, by growing and plowing
under plenty of clover, I not only secure nitrogen from the air and
liberate potassium from the soil but also liberate the phosphorus
from the raw rock phosphate applied to the soil. In beginning the
use of raw phosphate where the supply of organic manures is limited,
I apply one ton of phosphate and 600 pounds of kainit in intimate
connection, turn them under, preferably with organic matter, then
add ground limestone if needed, and thus prepare to grow clover.
By far the most important agencies under the farmer's control for
the liberation of plant food are the decomposition products of
fermenting or decaying organic matter, such as green manures, crop
residues and ordinary farm manures. In the decomposition of these
organic materials sour or acid products are formed. Thus vinegar,
containing acetic acid, is formed from the fermentation of apple
juice, hard cider being an intermediate product. Sweet, chopped,
immature field corn becomes sour silage in the silo, lactic, acetic,
carbonic and other acids being formed. By a similar process cabbage
is turned into sauerkraut. Likewise sweet milk becomes sour, with
the formation of lactic acid. Oxalic, citric, tartaric, succinic,
malic, gallic and tannic are other well-known organic acids. Some of
these are contained in the sap or juice of certain plants, and these
or others are formed when crop residues are decomposed in the soil.
In the ultimate decomposition of organic matter the carbon appears
in the form of carbon dioxid which when combined with water forms
carbonic acid. Though this is a very weak acid, its solvent action
is very important.
But, in addition to the various organic acids and carbonic acid, we
have also to consider the formation of nitric acid in connection
with the decomposition of organic manures. Nitric acid is one of the
strongest known, and in solvent power it is excelled by no single
acid. The nitrogen contained in crop residues and other organic
manures is chiefly in chemical combination with carbon, oxygen and
hydrogen, much of it in insoluble protein compounds. Normally this
organic nitrogen is transformed in the soil, first into ammonia
nitrogen, next into nitrite nitrogen, and lastly into nitrate
nitrogen, these three transformations being effected by biochemical
action produced by different kinds of living microscopic organisms
called bacteria. Though detectable amounts of free nitric acid do
not accumulate during this process of nitrification, the soluble
nitrate or final product is formed by the action of nitric acid upon
a mineral base, such as calcium, magnesium, or potassium, which may
have been in the soil in insoluble form, so that the nitrogen must
pass through the form of nitric acid in the transformation into
nitrates.
While the organic matter applied to the soil contains about twenty
times as much carbon as nitrogen, and while corresponding amounts of
carbonic acid and important amounts of intermediate organic acids
must be formed, it is of much interest to know that even the nitric
acid formed in the transformation of organic nitrogen to nitrate
nitrogen in sufficient quantity for a given crop is seven times as
much acid as would be required to convert raw rock phosphate into
soluble phosphate to furnish the phosphorus required for the same
crop. A knowledge of this definite quantitative relationship should
help us to appreciate the possibilities of decaying organic manures
in the important matter of making plant food available, including
potassium, calcium and magnesium as well as phosphorus and nitrogen.
The value of rye, rape, buckwheat and other non-legumes when used as
green manures is very largely due to the liberation of plant food by
their decomposition in contact with the natural phosphates, potash
and other minerals contained in the soil. The farmer has no more
important business than that of making plant food available,
especially by supplying liberal amounts of decaying organic matter.
The following suggestions are offered to the land owner:
To enrich the soil apply liberal amounts of limestone, organic
manures and phosphorus.
To enrich the seller apply small amounts of high-priced "complete"
commercial fertilizers.
Thus the average of seventy-three "Cooperative Fertilizer Tests on
Clay and Loam Soils," extending into thirty-eight different counties
in Indiana (Bulletin 155), shows 13 cents as the farmer's profit
from each dollar spent for "complete" fertilizers used for corn,
oats, wheat, timothy, and potatoes, if valued in the field at 40
cents a bushel for corn, 30 cents for oats, 80 cents for wheat, 50
cents for potatoes, and at $10 a ton for hay, over and above the
extra expense for harvesting and marketing the increase, and of
course the soil grows poorer, because the crops harvested removed
much more plant food than the fertilizers supplied.