Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

alternative farming—even as the scientific basis of agrochemistry helped
explain traditional practices.
Nineteenth-century experiments showed that grazing animals process
only a quarter to a third of the nitrogen in the plants they ingest. So their
dung is full of nitrogen. Still, manure does not return all the nitrogen back
to the soil. Without fertilizers, periodically cultivating legumes is the only
way to retain soil nitrogen and still harvest crops over the long run. Native
cultures around the world independently discovered this basic agricultural
truth.
In 1838 Jean-Baptiste Boussingault demonstrated that legumes restored
nitrogen to the soil, whereas wheat and oats could not. Here at last was the
secret behind crop rotations. It took another fifty years to figure out how
it worked. In 1888 a pair of German agricultural scientists, Hermann Hellriegel
and Hermann Wilfarth, published a study showing that in contrast
to grains, which used up the nitrogen in the soil, legumes were symbiotic
with soil microbes that incorporated atmospheric nitrogen into organic
matter. By the time the pair of Hermanns figured out the microbial basis
for the nitrogen restoring properties of beans, peas, and clover, the agrochemical
philosophy was already entrenched, spurred on by the discovery
of large deposits of guano off the Peruvian coast.
Peruvians had known of the fertilizing effects of guano for centuries
before the conquistadors arrived. When scientific explorer Alexander von
Humboldt brought a piece collected from the Chincha Islands back to
Europe in 1804 the curious white rock attracted the attention of scientists
interested in agricultural chemistry. Situated off the arid coast of Peru, the
Chincha Islands provided an ideal environment where huge colonies of
nesting seabirds left tons of guano in a climate rainless enough to preserve
it. And there was a lot—in places the Chincha guano deposits stood two
hundred feet thick, a mountain of stuff better than manure. Phosphaterich
guano also has up to thirty times more nitrogen than most manures.
Recognition of the fertilizing properties of guano led to a nineteenthcentury
gold rush on small islands composed almost entirely of the stuff.
The new system worked well—until the guano ran out. By then the widespread
adoption of chemical fertilizers had shifted agricultural practices
away from husbandry and nutrient cycling in favor of nutrient application.
The first commercial fertilizer imported to the United States inaugurated
a new era in American agriculture when John Skinner, the editor of the
American Farmer, imported two casks of Peruvian guano to Baltimore in
1824. Within two decades, regular shipments began arriving in New York.
dirty business 185