Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

in sodium sulfate and sodium carbonate, whereas seawater was enriched in
sodium chloride. The salts in the soil were weathering out of rocks, dissolving
in soil water, and then reprecipitating where the water evaporated.
He reasoned that drier areas had saltier soil because rain sank into the
ground and evaporated in the soil. So just as greater rainfall leached the
alkali from the soil, repeated flooding could flush salts from the ground.
Collaborating with farmers eager to improve their land, Hilgard also
advocated mulching to reduce evaporation of soil moisture. He experimented
with using gypsum to reclaim alkali soils. On New Year’s Eve 1893
the San Francisco Examiner trumpeted Hilgard’s successful transformation
of “alkali plains to fields of waving grain.” Later that year, on August 13, the
Weekly Colusa Sun went so far as to assert that Hilgard’s work was worth
“the whole cost of the University.”
Whereas Hilgard’s Mississippi work showed the importance of geology,
topography, and vegetation to soil development, his California work
stressed the importance of climate. In 1892 Hilgard published a landmark
report that synthesized data from around the country to explain how soils
formed. He explained why soils rich in calcium carbonate typical of the
West were unusual in the East, and how greater temperature and moisture
in the tropics leached out nutrients to produce thoroughly rotten dirt.
Hilgard’s report laid out the basic idea that the physical and chemical character
of soils reflect the interplay of a region’s climate and vegetation working
to weather the underlying rocks. Soils were a dynamic interface—
literally the skin of the earth.
Before Hilgard’s synthesis, soil science was dominated by perceptions
based on the humid climates of Europe and the eastern United States. Differences
between soils were thought simply to reflect differences in the
stuff left over from the dissolution of different rocks. By showing that climate
was as important as geology, Hilgard showed that soil was worthy of
study in its own right. He also championed the idea that nitrogen was the
key limiting nutrient in soils based on observed variations in their carbon
to nitrogen ratio and thought that crop production generally would
respond greatly to nitrogen fertilization.
Now recognized as one of the founding fathers of soil science, Hilgard’s
ideas regarding soil formation and nitrogen hunger were ignored in agricultural
colleges back East. In particular, South Carolina professor Milton
Whitney championed the view that soil moisture and texture alone controlled
soil fertility, maintaining that soil chemistry didn’t really matter
because any soil had more nutrients than required by crops. What was
dirty business 191