Environmental Engineering Reference
In-Depth Information
Box 8.5
Farmland Needed for America's Draft Animals in 1918
The total number of draft animals working on America's farms peaked during the
second half of the second decade of the twentieth century at nearly 27 million, includ-
ing more than 21 million horses and more than 5 million mules, with working stock
two years and older making up about 85% of that total, or nearly 23 million animals
(USBC 1975). With an average daily need of 4 kg of grain for working animals and
2 kg of concentrate feed for the rest (Bailey 1908), the annual concentrate feeding
requirement would have been at least 35 Mt of corn and oats. With prevailing yields
at about 1.5 t/ha for corn and 1.2 t/ha for oats and with three-quarters of all grain
supplied by corn, this would have required the planting of about 25 Mha of feed
grains.
Working horses also needed at least 4 kg of hay a day, while 2.5 kg of hay a day
were enough for nonworking animals. Hay requirements would have thus added up
to no less than 35 Mt/year. With average hay yields of between 2.5 and 3 t/ha, some
13 Mha of hay had to be harvested annually. The total land required to feed America's
draft animals was thus around 38 Mha, or 26% of all area harvested in those years
and signii cantly more than the area planted to exported crops (equal to about 17%
of the total). For comparison, the USDA calculated the total feed requirements for 1918
to be just short of 37 Mha (or 25% of the total), an excellent coni rmation of my
independently derived total.
higher output of concentrate feed (cereal and leguminous grains) besides the rough-
ages (grasses, straw) needed by ruminants.
Traditional agriculture of the early modern era (1500-1750) and of the great
industrialization period (1750-1900) was still powered only by animate energies
(human and animal muscles); it renewed soil fertility only by fallowing, the recycling
of organic wastes, and rotation with leguminous crops; and it relied on a diversity
of local cultivars. But cumulative improvements in agronomic management raised
labor productivity and brought the best yields very close to the peaks attainable
with premodern inputs. An hour of medieval i eld labor produced just 3-4 kg of
grain; by 1800 the European mean was around 10 kg, and by 1900 it was well over
40 kg. And net energy gains in grain production—the quotients of available food
energy and overall animate energy inputs—rose even more impressively, from less
than 25 for typical medieval harvests to around 100 by 1800 and to 400-500 a
century later (Smil 1994). These gains allowed masses of rural labor to shift into
urban manufacturing, construction, and transportation sectors. In the United States,
more than 80% of the labor force was in agriculture in 1800; a century later the
share was down to 42% (USBC 1975).
