Environmental Engineering Reference
In-Depth Information
tors built on this basis to develop practical mass-
produced machines: Cyrus McCormick in 183l and
Obed Hussey in 1834. The first harvester was patented
in 1858, the twine knotter was introduced by John
Appleby in 1878, and it perfected the first fully mechani-
cal harvester, a machine that was adopted with great
rapidity, making possible large expansion of wheat-
growing area before the end of the century. The peak of
horse-drawn harvesting was reached when a combined
header and thresher was marketed by the Stockton
Works during the 1880s. Housers, the company's stan-
dard combines, cut two-thirds of California's wheat by
1900; the largest ones needed up to 40 horses and could
harvest a hectare of wheat in less than 40 minutes. Such
machines took animal-powered fieldwork to its practical
limit: harnessing and guiding 16-40 horses was a logistic
challenge. The time was ripe for a much more concen-
trated source of tractive power.
Horse power brought enormous time savings. By
1900 the most productive combination of horses, imple-
ments, and machines reduced required human labor by
95% compared with oxen-powered cropping in 1800.
Energy costs are not so easily appraised. Net human
energy—energy spent above the basic survival rate and
equal to about 1.5 BMR—is fairly closely approximated
by assuming an average exertion in traditional farming
tasks equal to 4 BMR; 1 h of farming then costs 700 kJ.
Since draft animals are kept solely for traction, their total
annual feeding costs must be charged against the hours
actually worked: a horse costs about 30 MJ/h, an ox 25
MJ/h. With these realistic assumptions the comparison
shows little increase in overall energy cost. When deleting
the hauling of grain to granary, to make the two data sets
even more operationally comparable, the totals are virtu-
ally the same. This near-identity is clearly fortuitous, but
the similarity is not surprising. The useful work to be
done was the same, harvesting about 1.3 t/ha of wheat,
and the animate power, with an efficiency of 15%-20%
for both humans and beasts, was the only direct ener-
gizer. But where in the early nineteenth century 1 h of
labor was aided by draft work worth about 9 MJ, by the
end of the century 1 h of labor in California fields con-
trolled some 220 MJ of horse work. Farmers ceased
to be the key energizers of the process and became con-
trollers of larger energy flows.
6.4 Cropping Intensification
Agricultural intensification has three key ingredients:
water, nutrients, and crop diversity. Two old Chinese
peasant's sayings convey perfectly the dominance of these
needs: ''Whether there is a harvest depends on water;
how big it is depends on fertilizer'' and ''Plant millet
after millet and you will end up weeping.'' Water and
nutrients open the photosynthetic work gates in intensive
farming whose performance cannot be maintained at
high levels with successions of monocultures: irrigation,
fertilization, and crop rotations are thus the three princi-
pal roads to agricultural intensification. The relation be-
tween crop yields and water needs is complex, involving
a host of environmental and genetic variables (Dooren-
bos and Kassam 1979; Rick 1990), but the total seasonal
need is commonly about 1,000 times the mass of the
harvested grain. Up to 1500 t of water are needed to
grow 1 t of wheat; about 600 t of water suffices for 1 t
of corn. With harvest indices no higher than 0.30-0.35,
total water needs for the leading C
3
cereals are at least
300 mm and up to 500 mm.
Cultivation in arid and semiarid regions, whose annual
precipitation may be less than 100 mm and rarely
surpasses 250 mm, requires irrigation as soon as the
