Environmental Engineering Reference
In-Depth Information
Vicia) and clovers (Trifolium and Melilotus). These
plants fix 100-300 kg N/ha per year and, where climate
allows, their winter growth of three to four months adds
at least 30-60 kg N, enough to produce a good summer
cereal crop. In the long run the provision of adequate N
is of such importance that intensive agricultures cannot
do without the N-fixing legumes and thus plant them
in edible varieties. This desirable practice was perhaps
the most admirable indirect energetic optimization in
traditional farming, present in all intensive agricultural
systems that relied on complex crop rotations.
The cereal-legume link was notable everywhere: Chi-
na's soybeans, beans, peas, and peanuts alternating with
millets, wheat, and rice; India's lentils, peas, and chick
peas, with local grains, wheat, and rice; Europe's peas
and beans, with wheat, barley, oats, and rye; and West
Africa's peanuts and cowpeas, with millets. Food legumes
left rather large quantities of N (10-40 kg/ha) for the
subsequent grain crops, and while their absolute harvests
were lower than those of grains, they yielded at least
50% more protein per hectare than cereals. Moreover,
legumes, with lysine, complement the cereals, which are
deficient in this amino acid. Soybeans and peanuts also
provided edible oils to enhance the low energy density
of vegetarian meals, and oilseed cakes and legume resi-
dues make excellent high-protein feeds or fertilizers.
These quality considerations make any simple energy re-
turn calculations irrelevant, especially when the rotations
are seen in wider agroecosystemic settings as excellent
ways to reduce monocultural vulnerability to pests, limit
soil erosion, and improve the tilth.
Cultivated areas grew, but yields showed hardly any up-
ward trend because agronomic practices changed only
very slowly. This is the key paradox, the principal advan-
tage versus the fundamental weakness of traditional
agricultures (subsistence peasant societies). Unlike the
simpler survival cultures of foragers, traditional agricul-
tures have been able to support much higher population
densities by expanding cultivated land, gradually improv-
ing its productivity, and eventually bartering some prod-
ucts or services. Normal years provided a small food
surplus, and these arrangements were, at least theoreti-
cally, renewable. Yet these peasant societies, with their
high fertility rates and low per capita food production,
lived barely above the existential minima and were always
vulnerable to famines. This pattern of permanent misery,
recurrent hunger, and massive death persevered in parts
of Europe into the nineteenth century (for instance, the
Irish famine of 1846-1851). It persisted throughout
most of the poor world until the 1950s, and it was still
in place in the poorest parts of sub-Saharan Africa at the
beginning of the twenty-first century.
The most important difference between commercial
agriculture, with its assured food surpluses, and vulner-
able peasant farming is, not surprisingly, in their diver-
gent energy conversion strategies. As Seavoy (1986)
argued, this difference is perhaps best elucidated by pos-
ing a seldom asked question: Why do peasant societies
increase their populations to the maximum carrying ca-
pacity during normal crop years and expose themselves
periodically to seasonal hunger or famine during consec-
utive harvest failures? Moreover, why has this happened
even in societies with low population densities, high soil
fertilities, and fairly elaborate farming techniques? De-
spite enormous cultural differences, traditional peasant
societies shared a strong preference for subsistence com-
6.5 Traditional Agricultures
For most of recorded history, increases in agricultural
production came from the expansion of cultivated lands.
