Environmental Engineering Reference
In-Depth Information
significance to the concurrent diffusion of steam power.
Industrialization would have been impossible without
population growth, and the higher nitrogen supply
allowed for higher population density per unit of arable
land and for slow but steady improvement of the average
diet.
The effects of these advances on human energy expen-
ditures were noted in section 6.4. The effects on yields
cannot be so easily demonstrated because many older fig-
ures are given as seed/yield ratios (these were sometimes
negative) and the records show wide year-to-year fluctu-
ations. Carolingian wheat ratios were no better than 2; in
thirteenth-century England they rose to 3-4 (maxima
5.8). This translates to just above 500 kg/ha, and a dou-
bling of this rate was irreversibly achieved only some 500
years later, a gain averaging just 2%/decade (Stanhill
1976). The yield surge came only between 1820 and
1860, a result of land drainage, crop rotations, and man-
uring. By the early 1850s the national mean surpassed
2 t/ha.
Although at that time British agriculture was still
purely solar in terms of mechanical energy and nutrient
provision, it was already benefiting from coal-based man-
ufactures (better machinery). Indirect fossil energy subsi-
dies also pushed Dutch yields above 1 t/ha by the year
1800. In contrast, pre-1900 French wheat yields rose
only slowly, and there was no gain for the extensively
grown U.S. crop. The subsistence capacities of European
farming doubled from 2-2.5 people/ha of arable land in
the Middle Ages to 4-5 people/ha by 1800, and in the
most intensely cultivated regions they doubled again by
1900, when farming was changing into a new energetic
hybrid where solar radiation was combined with substan-
tial inputs of fossil energies (see sections 10.4 and 10.5).
