THE NITROGEN PROBLEM AND ITS ECONOMICAL SOLUTION
IN THE previous chapter emphasis has been laid upon the fact that
plants as well as animals must have food, and that the neglect or
ignorance of this factor in American agriculture has led to soil
depletion and land ruin on vast areas, especially in the older
states.
It has been shown that of the ten essential elements of plant food,
five are provided by natural processes without the intervention of
man; that, of the remaining five, potassium is the most abundant in
normal soil, but requires liberation by good systems of farming;
that ground natural limestone is the ideal material with which to
supply calcium and to prevent or correct soil acidity; and that if
dolomitic limestone be used magnesium is also supplied in suitable
form for plant food, Thus only nitrogen and phosphorus remain for
consideration.
Keeping in mind that systems of permanent profitable agriculture in
America must be founded upon an intelligent understanding of the
foundation principles involved, let us pray for strength to
acknowledge the truth and cease trying to deceive ourselves. The
truth is that by soil enrichment alone the average crop yields of
the United States could be doubled, with the same seed and seasons
and with but little more work than is now devoted to the fields; and
we should cease trying to deceive ourselves in the hope or belief
that the fertility of our soil will be maintained if we continue
year after year to take crops from the land and fail to make
adequate return.
Nitrogen is both the most abundant agriculturally and the most
expensive commercially of all the elements of plant food; and yet
there is a method by which it can be secured not only without money
but with profit in the process. The percentage of nitrogen in normal
soils decreases with depth, so that subsoils are almost devoid of
nitrogen. This would be more generally understood if it were known
that the supply of soil nitrogen in humid countries is contained
only in the organic matter.
This organic or vegetable matter consists of the partly decomposed
residues of plants, including the roots and fallen leaves which may
accumulate naturally, and the green manure crops, crop residues and
farm manure which may be supplied in farm practice. Thus the
nitrogen of a soil is measured approximately by its content of
organic matter; and, vice versa, the percentage of nitrogen is an
approximate measure of the organic matter, because nitrogen is a
regular constituent of the organic matter normally contained in
soils. Consequently if the organic matter of a soil is reduced the
supply of nitrogen is also reduced.
In the most depleted soils nitrogen is usually the most deficient
element, although it may not be the only deficiency. Thus in the
depleted "Leonardtown loam," which occupies such extensive areas of
land in Southern Maryland, near the District of Columbia, and which
has been to a large extent agriculturally abandoned after one or two
centuries of farming, only 900 pounds of nitrogen are found in the
plowed soil of an acre--that is, in 2,000,000 pounds of surface
soil, corresponding to about 6-2/3 inches an acre. This total amount
if made available would be sufficient for only six such crops of
corn as are actually produced on our best land in good seasons, and
yet it is four times as much as is contained in an equal weight of
the subsoil.
The average prairie land of the Corn Belt contains only 5000 pounds
of nitrogen in the plowed soil of an acre 6-2/3 inches deep, whereas
a 100-bushel crop of corn removes 150 pounds of nitrogen from the
soil. A simple computation shows the supply in the plowed soil to be
sufficient for only 33 such crops. Even the 100-bushel crop of corn
per acre is known to have been produced in many places on
exceptionally rich land, and yet the ten-year average yield in the
United States is only 25 bushels to the acre.
200 Per Cent for Nitrogen
On Broadbalk Field at Rothamsted, England, wheat has been grown on
the same land every year for about two-thirds of a century. As an
average of the sixty years, 1852 to 1911 the yield was 12.6 bushels
an acre on unfertilized land, 14.6 where mineral plant food was
annually applied, 20.3 where nitrogen salts alone were used, and 37
where both nitrogen and mineral plant food were applied.
During the thirty years, 1882 to 1911 the average yields were 11.7
bushels an acre on the unfertilized land, 14 with minerals, 18.7
where only nitrogen salts were used, and 38 where both nitrogen and
minerals were regularly supplied.
These absolute data from the oldest agricultural experiment station
in the world should help us to understand why the ten-year average
yield of wheat is 33 bushels an acre for all of Great Britain,
37-1/2 for England alone, and only 14 for the United States.
The application of nitrogen increased the yield of wheat by 24
bushels an acre--from 14 to 38 bushels--as an average of the last
thirty years, following an average increase of 26.3 for the nitrogen
applied during the previous thirty years. It is true that the cost
of the fertilizers used exceeded the value of the increase in yield;
but let us bear in mind that this truth does not destroy the other
truth.
Prove all things, and hold fast that which is good. It is a good
fact that 1218 bushels of wheat were produced by the application of
nitrogen to an acre of land during a period of sixty years, over and
above the produce of another acre which differed only by not
receiving nitrogen; whereas the total produce from an acre of
unfertilized land was only 756 bushels during the same sixty years.
It is a good fact that the increase alone from the nitrogen applied
is more than twice the total yield of the unfertilized land during
the last thirty years, and he does well who holds fast this fact.
It is also a good fact that as an average of sixty years the yield
of barley was increased by 21.6 bushels an acre by nitrogen; that
nitrogen increased the yield of hay on permanent meadow land at
Rothamsted by 1-1/2 tons an acre as a fifty-year average; and that
nitrogen increased the average yield of potatoes by 88 bushels as an
average of twenty-six years; while the average of the unfertilized
land was only 51 bushels an acre, these increases in barley, bay,
and potatoes being obtained over and above the yields where minerals
alone were used.
Where Is Nitrogen?
If nitrogen has such enormous power to increase the yield of our
great staple farm crops then we may well inquire, Where is nitrogen,
and how can it be secured economically and utilized profitably in
practical agriculture?
The weight of the atmosphere is 15 pounds to the square inch. This
means that a column of air 1 inch square taken to the full height of
the terrestrial atmosphere weighs 15 pounds. More than three fourths
of the air is nitrogen. Since there are 43,560 square feet in one
acre, it follows that the nitrogen in the air above each acre of the
earth's surface amounts to 70,000,000 pounds, or nearly 500,000
times the 150 pounds of nitrogen required for a hundred-bushel crop
of corn. The leaves of the corn plant are blown about by the wind
carrying 75-1/2 per cent of nitrogen, but cannot utilize an ounce of
this supply.
Many people know that clover and other legumes have power, through
the bacteria which inhabit their root tubercles, to feed upon the
inexhaustible supply of atmospheric nitrogen which freely enters the
pores of the soil; but who knows how much nitrogen is taken from the
air by a given crop of clover? Not one in a thousand can answer this
question; and meanwhile our continued agricultural and national
prosperity depends in large part upon the possibility of wide
dissemination and practical application of a quantitative knowledge
of the nitrogen problem.
As a rule the so-called "practical" farmer is a theorist. He first
believes that the virgin soil is inexhaustible, even though cropped
continuously. Later he clings to the popular theory that the
rotation of crops will maintain the productive capacity of the land;
and it is safe to say that a large majority of the farmers of the
United States gladly hold to the erroneous theory that clover grown
once every three to five years will increase and permanently
maintain the fertility of the soil.
The fact that clover was grown for generations on the lands of the
older Eastern states until the clover crop itself finally failed on
millions of acres now agriculturally abandoned is overlooked or
forgotten by present-day farmers, especially by the descendants of
those who have gone West and settled on new, rich lands.
Six Facts and a Question
The following six facts will furnish a comprehensive basis for the
solution of the nitrogen problem in practical general agriculture:
(1) To produce 100 pounds of grain requires about 3 pounds of
nitrogen, of which 2 pounds are deposited in the grain itself and 1
pound in the straw or stalks.
(2) In live-stock farming one-fourth of the nitrogen in the food
consumed is retained in the animal products--meat, milk, wool, and
so on--and three-fourths may be returned to the land in the
excrements if saved without loss.
(3) When grown on soils of normal productive capacity legumes secure
about two-thirds of their total nitrogen from the air and one-third
from the soil.
(4) Clover and other biennial or perennial legumes have about
two-thirds of their total nitrogen in the tops and one-third in the
roots, while the roots of cowpeas and other annual legumes contain
only about one-tenth of their total nitrogen.
(5) Hay made from our common legumes contains about 40 pounds of
nitrogen per ton.
(6) Average farm manure contains 16 pounds of nitrogen per ton.
Question: How many tons of average farm manure must be applied to a
40-acre field in order to provide as much nitrogen as would be added
to the soil by plowing under 2-1/2 tons of clover per acre? Answer:
400 tons.
Either method will furnish about as much nitrogen as would be taken
from the soil by a 50-bushel crop of wheat, a 75-bushel crop of corn
or a 100-bushel crop of oats per acre. The decision by the
individual between live-stock farming and grain farming should be
based upon preference and profit rather than upon the erroneous
teaching that farm manure is either essential or sufficient for the
maintenance of soil fertility in this country.
Bread is the staff of life, and many must sell grain. I do not
advise all grain farmers to become live-stock farmers; but I do
advise both grain farmers and live-stock farmers to enrich their
soils by practical, profitable and permanent methods. Both classes
of farmers may secure new nitrogen--that is, they can positively
increase their nitrogen supply by sufficient use of legume crops.
How to Supply Nitrogen
The cotton-grower who sells cotton lint at 10 cents a pound and the
market gardener who sells from $100 to $300 worth of fruits and
vegetables from one acre may well make liberal use of commercial
nitrogen at 15 or 20 cents a pound; but if after deducting the cost
of harvesting, threshing, storing and marketing the average farmer
receives only 1 cent a pound for his grain and if 40 per cent of the
commercial nitrogen applied is lost by leaching, then the total crop
of grain would bring only enough money to pay for the nitrogen
required to produce it, at 20 cents a pound. We may sometimes advise
the American grain-grower to buy water with which to irrigate his
crop, but not to buy nitrogen with which to fertilize it.
If the grain farmer grows 40 bushels of wheat to the acre, clover
having been seeded on the same land in order to plow under the
equivalent of 1-1/2 tons of hay as green manure the following
spring, and follows this by a 60-bushel crop of corn and a 50-bushel
crop of oats, and this the fourth year by two crops of clover
aggregating 3 tons an acre, including 2 bushels of seed, he can thus
secure from the air about 180 pounds of nitrogen in the 4-1/2 tons
of clover. Moreover, if the first cutting of clover the fourth year
is left on the land and the threshed clover straw from the seed crop
and likewise all straw and stalks are returned to the soil, only 154
pounds of nitrogen an acre would leave the farm if the total grain
and clover seed were sold. With 80 cents a bushel for wheat, 50
cents for corn, 40 cents for oats and $8 for clover seed, the total
returns from the four acres would amount to $98.
On the other hand the live-stock farmer may grow two 60-bushel crops
of corn, followed by 50 bushels of oats and then 3 tons of clover
hay containing 120 pounds of new nitrogen. The four crops would
contain 350 pounds of nitrogen; and if the grain and hay and half
the corn-stalks are used for feed, with the straw and the remainder
of the stalks for bedding, it is likewise possible to replace the
230 pounds of nitrogen required for the grain crops, provided not
more than one-seventh of the manure is lost before being returned to
the land. The important weakness on the common live-stock farm lies
in the enormous waste of manure.
If 10 pounds of feed produce 1 pound increase in the live-weight of
the animals fed, and if they bring 6 cents a pound on the hoof, the
gross returns aggregate $107.50 from the four acres, barring losses
from accidents, animal diseases, and so on.
Thus, with a few established facts in mind, one can easily determine
how to maintain or even to increase the supply of nitrogen in the
soil, and without the purchase of nitrogen in any form; and it is
just as possible and just as necessary thus to provide the nitrogen
needed in grain farming as in livestock farming. When we consider
that animals destroy two-thirds of the organic matter in the food
consumed we find that as between the two systems above described the
organic matter or humus of the soil will be better maintained in the
grain system outlined.
Live-Stock or Grain Farming
For those who believe that live-stock farming must be adopted for
the maintenance of fertility on all farms, attention should be
called to the fact that there are 900,000,000 acres of farm-land in
the United States and only 90,000,000 head of live-stock equivalent
to cows, including all farm animals. Will the manure from one cow
serve to enrich 10 acres of land?
It should also be known that a hundred bushels of grain will support
five times as many people as could live for the same length of time
on the meat and milk that could be made by feeding the grain to
domestic animals. It is because of this fact that the consumer may
sometimes boycott meat or other animal products, while he never
boycotts bread; but let us hope that permanent systems will become
generally adopted in America, for the production of both grain and
live stock, so that high standards of living may be maintained for
all classes of people in this country.
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.