Agriculture Reference
In-Depth Information
crop—all the nitrogen, phosphorus, potassium, carbon, water,
and other minerals. Unless the crop is used in a small com-
munity where all the excrement of animals and humans are
returned to the soil, a field immediately becomes less fertile
after harvest, so farmers return nutrients to the soil before
planting the next crop.
Most farmers in the modern world do not return all the
nutrients they take from the land. Chemical fertilizers typi-
cally consist of only nitrogen (N), phosphorus (P), and potas-
sium (K). Farmers will periodically apply lime to restore a
proper pH balance in the soil. However, they do not apply
many micronutrients because it would not increase yields.
Plants need very few micronutrients in any one year and
ample amounts are already present in most soils. A number
of experimental fields at universities have raised crops for
decades (in some cases over a century), and yields continue to
rise even when fields receive only N, P, and K (and occasion-
ally the micronutrients sodium and magnesium).
Many farmers to-day are anxious because they can no
longer make good farmyard manure, but must rely more
on artificials, and grow cereals more often. Will they
injure the soil? The Broadbalk results show that, apart
from disease, the yield of wheat can be kept up indefi-
nitely by proper artificials.
—Sir John Russell, director of Rothamsted Station, 1943,
quoted in Philip Conford,
The Origins of the Organic
Movement
(Edinburgh: Floris Books, 2001).
Has chemical fertilizer enhanced fertility in the last one
hundred years? Absolutely, but with one qualification. Most of
the yield gains witnessed over the past seventy years did not
derive from chemical fertilizer alone, but from new crop vari-
eties, machinery, and pesticides as well. In fact, new grain vari-
eties were sometimes created in response to the availability of
