Environmental Engineering Reference
In-Depth Information
curved metal plates joined to the plowshare. During the
second half of the eighteenth century, Western plows still
retained their heavy wooden wheels but carried well-
curved iron moldboards. Steel replaced cast iron begin-
ning in the 1830s.
In most soils, plowing leaves behind relatively large
clods that must be broken up before seeding. Hoeing is
too slow and too laborious, and hence various harrows
were used by all old plow cultures. After plowing, har-
rowing, and leveling, the ground was ready to be seeded.
Although seed drills were used in Mesopotamia as early
as 1300
B
.
C
.
E
., and sowing plows were used by the Han
Chinese, broadcast seeding by hand (wasteful and result-
ing in uneven germination) remained common in
Europe until the nineteenth century. Simple drills, drop-
ping seeds through a tube from a bin attached to a plow,
started to spread, first in northern Italy during the late
sixteenth century, and many innovations turned them
before too long into complex seeding machines. Sickles
were the first metal harvesting tools to replace short
sharp stonecutters. Serrated (the oldest designs) or with
smooth edges, and with semicircular, straight, or slightly
curved blades, they have been used in countless varia-
tions. More efficient scythes, equipped with cradles for
grain reaping, were used for harvesting larger areas.
But sickle harvesting minimized grain losses, and it was
retained throughout Asia in cutting easily shattered rice.
Mechanical reapers came only after 1800. Harvests were
brought home as sheaves carried on heads, in panniers
hung on shoulder beams or sides of animals, and in
wheelbarrows, carts, and wagons. A great deal of energy
was spent on crop processing. Grain spread on a thresh-
ing floor was beaten with sticks or flails, sheaves were hit
against grates or pulled across special combs. Animals
treaded the spread grain or pulled heavy sleds or rollers.
Winnowing, the separation of chaff and dirt from grain,
was done manually with baskets and sieves, later with
crank-turned fans. Tedious manual labor was also needed
for grain milling before animals, water, and windmills
mechanized the task. Oil was extracted from seeds by
manual or animal-operated presses, as was the juice from
cane.
All traditional agricultures grew a variety of grain, oil,
fiber, and feed crops, but the standard agronomic se-
quence was performed most often when cultivating cere-
als. The plowless Mesoamerican societies, which relied
on corn, shared this practice, and even the Incas were
only a partial exception: at high elevations they planted
potatoes, but at lower altitudes they also cultivated corn,
and on the high-lying Andean Altiplano, quinoa grain.
There were many cereals of local or regional importance,
but the main genera gradually diffused worldwide from
their areas of origin. Wheat spread from the Near East;
DNA testing pinpoints the domestication of einkorn
wheat to the Karacada˘ region in Turkey (Heun et al.
1997). Cereal gathering in the region dates to 19,000
years ago, and the earliest indehiscent (nonshattering)
domestic wheat to about 9,250 years ago (Tanno and
Willcox 2006). Rice came from Southeast Asia, corn
from Mesoamerica, and millets from China (Cowan and
Watson 1992). Grains became dominant because of a
combination of evolutionary adjustments and energetic
imperatives.
Foraging societies depended on a wide variety of
plants, and either tubers or seeds provided most of their
food energy. But the water content of fresh tubers is too
high for long-term storage in the absence of effective
temperature and humidity controls. The Incas solved
the problem by making dehydrated chu˜o (produced
by trampling and alternate freezing and drying), which
