Environmental Engineering Reference
In-Depth Information
6.2 Evolution of curved moldboard plows. (a) Traditional
Chinese plow. (b) Eighteenth-century French plow. (c) Ameri-
can steel beam plow of the mid-nineteenth century. From Smil
(1994).
for people, feed for animals, organic wastes that were
recycled to replenish soil fertility, and fuels that energized
the smelting of metals needed to make simple farm tools.
Consequently, traditional farming was, at least in theory,
fully renewable because it relied on virtually immediate
conversions of solar energy flows. But this renewability
was no guarantee of sustainability. Conversion of forests
to farmland, and the use of wood for fuel and charcoal,
steadily depleted accumulated phytomass energy, and
poor agronomic practices lowered soil fertility and often
caused excessive erosion or desertification. Such envi-
ronmental degradations lowered yields or even caused
the abandonment of cultivation. These agricultures also
shared the fundamental agronomic sequence of plowing,
seeding, harvesting, and crop processing that was dic-
tated by the nearly universal dominance of grains.
All the Old World's high cultures were creations of
grain surplus, and regular plowing was their energetic
hallmark (fig. 6.2). Plowing's antiquity is attested by the
fact that both the Sumerian cuneiform characters and
the Egyptian glyphs have pictograms for plows (Jensen
1969). Plowing opened the soil for planting of small
seeds on scales vastly surpassing those of hoe-dependent
farming. The first primitive scratch plows (ards), com-
monly used after 4000 B . C . E . in Mesopotamia, were just
pointed wooden sticks with a handle. Later most of
them were tipped with metal, but for centuries they
remained symmetrical (draft line in a vertical plane with
the beam and share point) and light, able only to open a
shallow furrow for seeds and leave the cut weeds on the
surface. These plows were the mainstay of both Greek
and Roman farming, and they were found in parts of the
Middle East, Africa, and Asia well
into the twentieth
century.
Addition of a moldboard was a fundamental improve-
ment. A moldboard guides the plowed-up soil to one
side, turns it partly or totally over, buries the cut weeds,
and cleans the furrow bottom. A moldboard also makes
it possible to till a field in one operation rather than by
the cross-plowing required with ards. The moldboard's
draft line is displaced slightly toward the side of the
turned-up soil, making the plow asymmetrical. The first
moldboards were just straight pieces of wood, but before
the first century B . C . E ., the Han Chinese introduced
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