Environmental Engineering Reference
In-Depth Information
wastes) have just 0.5%-1.5% of the element. Conse-
quently, effective fertilization required laborious appli-
cations of huge amounts of organic matter (annual
maxima up to 40 t/ha), but energy gained in additional
yields was 10-20 times the energy cost of fertilization.
Crop rotation was the third key ingredient of farming
intensification. Leguminous species, fixing their own ni-
trogen and enriching the soil for subsequent crops, were
rotated with staple grains by every traditional agriculture.
Soybeans, beans, peas, and lentils were indispensable
sources of protein. The least intensive traditional prac-
tices could support just 1-2 people/ha of arable land,
and typical subsistence agricultures stagnated for centu-
ries at 2-3 people/ha. In contrast, the most intensive
agricultures of China and Western Europe, using irriga-
tion, recycling, crop rotation, and multicropping, could
support more than 7 people/ha, or with modest vegetar-
ian diets, 12 people/ha. Intensive agricultures had yields
up to nearly 50 GJ/ha and overall energy returns of 15-
20. Despite enormous cultural differences, traditional
peasant societies shared a strong preference for a subsis-
tence compromise by which mimimum levels of material
welfare and nutritional safety were acquired with the
least expenditure of energy inputs. By minimizing labor
inputs, peasants left themselves vulnerable to recurrent
famines.
Traditional societies relied on human and animal
muscles and on the combustion of biomass fuels. Human
labor dominated all ancient societies, from dynastic
Egypt to Rome. Classical Greece was no exception. The
civilization of philosophers who articulated the concept
of individual freedom was energized by plentiful and
cheap slave labor. Animals (tetrapoda) were more expen-
sive to keep and less flexible to use than andrapoda (liter-
ally ''man-footed,'' Homer's term in the Iliad), mostly
13.3 Declining agricultural labor, illustrated with average
inputs into U.S. wheat production.
bines revolutionized traditional farming and sharply
reduced the inputs of human labor (fig. 13.3).
Irrigation was the first component of intensified field
farming. Its antique origins are attested to by a variety
of simple water-lifting machines (sh¯d¯f, Archimedean
screw, paddle wheel, rope and bucket lift, s¯q¯ya, noria)
that were tediously powered by humans or animals. Lifts
were only 0.5-2.5 m, efficiencies no better than 20%-
30%, capacities 3-15 m
3
/h, and energy costs 100-250
kJ/m
3
for human-powered lifts and 4.5-6.5 MJ/m
3
for
animal water raising. But energy returns in additional
crop yields were high, 10-20-fold. Fertilization relied
solely on the recycling of organic matter. Nitrogen was
nearly always the limiting nutrient, but all common or-
ganic fertilizers (crop residues, manures, and human
