Environmental Engineering Reference
In-Depth Information
only tiny amounts of animal foodstuffs on festive occa-
sions, supported high population densities. The nation-
wide average was about 4.5 people per ha of sown land,
or at least 5.5 people/ha of arable area. Rice-growing
southern China could do even better, averaging 5.5
people/ha of arable land by the end of eighteenth
century and surpassing 7 people/ha by the late 1920s.
Double-cropping in the most intensively farmed areas
(summer rice, winter wheat, rapeseed, or broad beans)
could yield 36-48 GJ/ha, enough to feed 12-18 people.
But like other peasant societies, China was vulnerable to
recurrent famines caused by droughts and floods. During
the 1920s peasants recalled an average of three crop fail-
ures serious enough to cause famines, which lasted on av-
erage about ten months, affected 65% of farmed area per
county, forced 25% of people to eat bark and grasses, and
forced nearly 15% to leave their villages in search of food.
Even the most intensive traditional farming system could
not rid itself of this vulnerability.
The European experience was less harsh owing to
a more equable climate in the West and to generally
lower population densities. But Europe experienced
similar prolonged productivity stagnation, periodic deep
declines, and centuries of gradual intensification punctu-
ated by minor and major famines (Seebohm 1927; Abel
1962; Slicher van Bath 1963; Duby 1968; K. D. White
1970; Fussell 1972; Grigg 1992). Greek farming was
not as impressive as its contemporary Middle Eastern
counterparts, but the Roman experience, summarized by
Cato, Varro, Columella, Virgil, and Palladius, was influ-
ential until the seventeenth century. Roman mixed farm-
ing (unlike China, Europe always had a strong animal
husbandry component) included rotations of cereals and
legumes, plowing-in of green manures, often intensive
recycling of organic wastes, and repeated liming (using
chalk or marl).
Oxen, often shod, were the principal draft animals, a
good pair expected to plow 1 jugerum (2675 m
2
)/day
or 40 jugera/a of light soil (nearly 11 ha). Plows were
wooden, sowing was by hand, harvesting was done with
sickles (the Gallic reaper, described by Pliny and pictured
on a few reliefs, was not widely used), threshing was done
with flails, milling was manual, and the yields were low
and highly variable. All these realities changed only very
slowly during the millennium after the demise of the
Western Roman Empire. Notable changes included use
of the scythe instead of the sickle, shoulder collars for
horses, and (in some regions) the emergence of horses
as principal draft animals. Manuring was practiced with
varying intensities, legumes were grown in diverse rota-
tions, fallowing was common, and harvests remained ex-
tremely variable.
Times of relative prosperity, most notably 1150-1300
and 1450-1550, were marked by extensive conversions
of wetlands and forests to fields and by a greater variety
of companagium (accompaniments of the ubiquitous
bread). Decades of decline were marked by famines,
abandonment of villages, and soil erosion. Insecurity
remained common right up to the eighteenth century,
when fairly intensive cultivation became the norm with
better field implements, progressive abolition of fallow,
regular manuring, and diffusion of new cultivars. By far
the most important step was the adoption of standard
rotations, including legume cover crops, exemplified by
Norfolk's four-year succession of wheat, turnips, barley,
and clover, which at least tripled the rate of symbiotic
nitrogen fixation (Campbell and Overton 1993). Chor-
ley (1981) concluded that this step was of comparable
