Environmental Engineering Reference
In-Depth Information
Applications of calcium sulfate, and of marl or lime to correct excessive soil acidity
became common in better-off areas.
A slowly growing use of better-designed implements also accelerated during the
nineteenth century. By the middle of the century yields were rising in every important
farming region as the rapidly intensifying agriculture was able to supply food for
growing urban populations. After centuries of l uctuations, population densities
were rising steadily. In the most intensively cultivated Atlantic regions of the conti-
nent they reached 7-10 people/ha of arable land by the year 1900. But these levels
already rel ected considerable energy subsidies received indirectly as machinery and
fertilizers produced with coal and electricity. European farming of the late nineteenth
century became a hybrid: still critically dependent on animate prime movers but
increasingly benei ting from many inputs requiring fossil energy.
Modern Cropping
The gradual intensii cation of traditional farming involved innovations with imme-
diate effects on typical yields (and hence on the required land), as well as measures
that had only a marginal impact on harvests. Increasingly elaborate irrigation tech-
niques and regular recycling of organic wastes belonged to the i rst category: they
improved average harvests, or at least reduced the annual l uctuation in yields. On
the other hand, the substitution of animal draft for human labor or the adoption
of better i eld machinery brought much higher labor productivities but often had
only a minimal effect on average yields: by 1900, American i eld work was highly
mechanized (with large horse-drawn steel plows, grain reapers, binders, combines,
and steam-powered threshers)—but average grain yields remained low.
Major gains in terms of average land productivity came only with the assiduous
combination of crop rotations (particularly with the regular cultivation of pulses or
cover crops used as green manures), multicropping (reducing or eliminating fallow
periods), and high rates of organic (animal and human waste, composts) recycling.
Some of the most densely populated regions of Eurasia reached the highest levels
of crop productivity that could be supported without synthetic fertilizers and pes-
ticides and without improved cultivars; as already noted, by the 1920s China's
traditional farming could feed 5-7 people/ha of cultivated land, and similar levels
were reached in the most fertile parts of Japan, on Java, and in parts of Atlantic
Europe.
While these innovations reduced the area of agricultural land needed to secure
adequate diets, three trends had the opposite effect. The i rst one was higher
