Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

On a more optimistic note—as we ponder whether agriculture will be able
to keep up with the world’s population—we might take comfort in the
amazing twentieth-century growth in agricultural production.
Until the widespread adoption of chemical fertilizers, growth in agricultural
productivity was relatively gradual. Improvements in equipment,
crop rotations, and land drainage doubled both European and Chinese
crop yields between the thirteenth and nineteenth centuries. Traditional
agricultural practices were abandoned as obsolete when discovery of the
elements that form soil nutrients set the stage for the rise of industrial
agrochemistry.
Major scientific advances fundamental to soil chemistry occurred in the
late eighteenth and early nineteenth centuries. Daniel Rutherford and
Antoine Lavoisier respectively discovered nitrogen and phosphorus four
years before the American Revolution. Humphrey Davy discovered potassium
and calcium in 1808. Twenty years later Friederich Wöhler synthesized
urea from ammonia and cyanuric acid, showing it was possible to
manufacture organic compounds.
Humphrey Davy endorsed the popular theory that manure helped sustain
harvests because organic matter was the source of soil fertility. Then in
1840 Justus von Liebig showed that plants can grow without organic compounds.
Even so, Liebig recommended building soil organic matter
through manure and cultivation of legumes and grasses. But Liebig also
argued that other substances with the same essential constituents could
replace animal excrement. “It must be admitted as a principle of agriculture,
that those substances which have been removed from a soil must be
completely restored to it, and whether this restoration be effected by means
of excrements, ashes, or bones, is in a great measure a matter of indifference.
A time will come when fields will be manured with a solution ...prepared
in chemical manufactories.” 1 This last idea was revolutionary.
Liebig’s experiments and theories laid the foundation of modern agrochemistry.
He discovered that plant growth was limited by the element in
shortest supply relative to the plant’s needs. He was convinced that crops
could be grown continuously, without fallowing, by adding the right
nutrients to the soil. Liebig’s discovery opened the door to seeing the soil
as a chemical warehouse through which to supply crop growth.
Inspired by Liebig, in 1843 John Bennet Lawes began comparing crop
yields from fertilized and unfertilized fields on Rothamsted farm, his family’s
estate just north of London. An amateur chemist since boyhood,
Lawes studied chemistry at Oxford but never finished a degree. Nonethe-
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