Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

e the key elements of concern to agriculturalists. How to get enough of
them was the issue.
Even though nitrogen makes up most of our atmosphere, plants can’t
use nitrogen bound up as stable N 2 gas. In order to be used by organisms,
the inert double nitrogen molecule must first be broken and the halves
combined with oxygen, carbon, or hydrogen. The only living organisms
capable of doing this are about a hundred genera of bacteria, those associated
with the roots of legumes being the most important. Although most
crops deplete the supply of nitrogen in the soil, root nodules on clover,
alfalfa, peas, and beans house bacteria that make organic compounds from
atmospheric nitrogen. This process is as essential to us as it is to plants
because we need to eat ten preformed amino acids we can’t assemble ourselves.
Maintaining high nitrogen levels in agricultural soil requires rotating
crops that consume nitrogen with crops that replenish nitrogen—or
continually adding nitrogen fertilizers.
Phosphorus is not nearly as abundant as nitrogen, but it too is essential
for plant growth. Unlike potassium, which accounts for an average of 2.5
percent of the earth’s crust and occurs in rocks almost everywhere in forms
readily used as natural fertilizer, phosphorus is a minor constituent of rockforming
minerals. In many soils, its inaccessibility limits plant growth. Consequently,
phosphorus-based fertilizers greatly enhance a crop’s productivity.
The only natural sources of phosphorus other than rock weathering are
relatively rare deposits of guano or more common but less concentrated
calcium-phosphate rock. By 1908 the United States was the largest single
producer of phosphate in the world, mining more than two and a half million
tons from deposits in South Carolina, Florida, and Tennessee. Almost
half of U.S. phosphate production was exported, most of it to Europe.
By the First World War serious depletion of phosphorus was apparent in
American soils.
For extensive areas in the South and East the phosphorus is so deficient
that there is scarcely any attempt to raise a crop without the use of
phosphate compounds as fertilizers. ...Western New York and Ohio,
which not more than fifty or sixty years ago were regarded as the very
center of the fertility of the country, are very seriously depleted in this
element; and into them there is continuous importation of phosphate
fertilizer. 5
Early twentieth-century estimates of the amount of phosphorus lost in
typical agricultural settings predicted that a century of continuous crop-
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