Evening star., 1938-09-29
OF STARS,
MEN AND ATOMS
Notebook of Science ProSres'
in Field, Laboratory
and Study.
By THOMAS r. HENRY.


The soil Of the United States is losing
more than 100000 tons Of nitrogen =
year.
This gas, which constitutes about 80
per cent Of the atmosphere. is absolutely
essential to all life. Without 1t earth
would be q sterile waste. It plays the
most important part Of all the elements
in plant and animal growth.
It is being taken out Of the soil at q
rate Of nearly $4,000, 600 tons year. while
only about l7,000.000 tons are replaced.
Consequently the fertility OF the Nation
is suffering steady decline. This yearly
deficit in the nitrogen balance u one Of
the most significant findings Of the soil
specialists of the Department Of Agricul-
ture who have just reported to Secretary
Of Agriculture Henry A. Wallace. Their
reports form bulky volume Just issued
by the department.
Nature herself Is generous with nitro
gen, according to the report by Drs.
Oswald Schreiner and B. =. Brown, de-
partment biochemists. Over every acre
Of the North American Continent there
nitrogen in the air. Up to 4 depth Of 40
A4AIAlOo VA1C4C ID al 6VCI8&0 "a kCWI4y
10000 pounds per acre in the soil.
Plant life, however. cannot make use
Of the pure nitrogen Of the atmosphere.
1t must be combined with other elements
and gotten into the soil before 1t is Of
any use to them. Lightning discharges
form combinations of nitrogen and
oxygen. These unite with moisture in the
air to form more complex substances.
nitrous or nitric acid. These, in turn. are
washed out Of the atmosphere and into
the soil by rain or snow. which explains
the old saying that snow Is the poor
mans fertilizer" From five to seven
pounds per acre are added in this way.
There are also large group Of bac-
terra which live in the soil that have the
ability to draw free nitrogen out Of the
atmosphere into the soil and transform
1t into various compounds. essential to
plant life. These micro organisms are in
two groups One exists independently in.
the upper layers Of the soil and adds
about rs pounds per acre every year.
Those in the other group exist only in
association with the roots Of leguminous
plants-such as alfalfa, clover, peas and
beans-and are much more prolific hxers
Of nitrogen to the extent Of about 80
pounds per acre.
On an average close to so pounds per
acre are added to the soil Of the United
States. This is about the average which
land covered with vegetation requires.
The amount taken up by plants ranges
from about 40 to 200 pounds per acre.
Under primeyal conditions a greater part
Of this would return to the soil again.
The plants would die. decay and become
mixed with the earth. The complex or
ganic molecules in which they had incor-
porated the nitrogen would be broken up
and made available for new plant growth.
The animals that had eaten the plants as
the only source Of the nitrogen essential
to their growth also would die and 60
through the same process. A certain
amount Of the gas would be returned
from the soil to the air, but this would
be nearly balanced by the amounts put
back in the soil by rain and snow.
This balanced nitrogen account existed
all over the country when 1t was forest
and unplowed prairie. It was upset as
soon as agriculture started on . large
scale. The nitrogen escaped back to the
air much more easily from plowed
land. Crops, instead Of being allowed to
die and decay where they grew, were
sold in the form Of corn, wheat, cotton,
beef and pork-eventually to go back into
the soil again somewhere. but never to
give back their nitrogen to the place
from which they had taken 1t.
The loss. according to the report of the
Department Of Agriculture biochemists,
amounts to Is per cent Of the original
quantity Of the precious gas in the first
20 years after soil is brought under the
plow, 10 per cent in the next 20 years
and about per cent in the third two
decades. Eventually q new balance will
be struck, but at q much lower level Of
soil fertility.
The amounts Of nitrogen taken out Of
the soil must be replaced in the form Of
fertilizer. 1t Is never enough, however, to
replace only the amounts tGken 1by
the plants. Leaching from plowe1 bill
and erosion are sources of losses Of the
first magnitude. The Department Of
Agriculture data show that in few parts
Of the United States have the losses over
the last half century been entirely re-
placed.
Fertilization Is expensive. The report
urges q wider and more effective use of
nitrogen supplying leguminous crops,
farm manures which are rich source of
nitrogen, prevention Of soil erosion and
more use Of cover crops to prevent the
teaching Of the gas from the soil. The
greatest source of replacement, however,
must be artificial fertilizers.