Environmental Engineering Reference
In-Depth Information
weeding, and protection; work expenditures vary greatly
depending on the cleared vegetation, terrain, and crops.
Rappaport's (1968) quantifications of Tsembaga horti-
culture in the highlands of New Guinea were the first
solid account of the energetics of shifting farming. Grow-
ing nearly 40 species in their intercropped gardens, the
Tsembaga harvested annually 23.7-26.9 GJ/ha of edible
phytomass while expending l.48-l.63 GJ of energy above
basal metabolism, a 16-fold return on their efforts.
Not long after Rappaport's fieldwork a British team
studied coastal (Kaul) and highland (Lufa) New Guinea
tribes. It found that in spite of their low body weights,
apparently high metabolic efficiencies (see section 5.2),
and fairly sedentary lifestyle (walking and gardening
occupied @15% of their time), the tribes' food energy
returns were very low. With labor investments of 3.20
MJ/day (Kaul) and 5.73 MJ/day (Lufa) and food
intakes at about 33 MJ, the returns were just ten- and
sixfold (Norgan, Ferro-Luzzi, and Durnin 1974). The
corn harvest of the Guatemalan Kekchi Maya (16.4 GJ)
yielded a minimum 30-fold return (W. E. Carter 1969).
The Colombian Yukpa realized a 20-fold gain by grow-
ing corn, beans, manioc, and bananas (Ruddle 1974).
The Hanunoo cultivated 68 food species, of which 39
were also grown for medicinal, ritual, cosmetic, or manu-
facturing uses in complex, staggered plantings, preclud-
ing a reliable quantification of total edible yield (Conklin
1957), but their rice cultivation had at least a 16-fold
gain.
Other available figures support the conclusion that to-
tal labor inputs vary between 600 h/ha and 3200 h/ha
and that the energy returns of shifting cultivation are
11-fold to 15-fold for small grains (whether Southeast
Asian hill and swamp rices or African millets), 20-fold to
40-fold for most root crops, bananas, and good corn
yields, and maximally close to 70-fold for some roots
and legumes in excellent locations. One person requires
as much as 10 ha and as little as 2 ha of land in fallow
and under the crops, with the actually cultivated area
ranging from 0.1 ha to 1 ha. Compared to pastoralist
population densities of 1-2/km
2
, shifting cultivators'
densities of 30-40/km
2
are 1 OM higher, and their en-
ergy returns and security of food supply are almost invar-
iably superior.
Shifting agricultures shared a number of energetic
commonalities. Clearings were chosen close to the settle-
ments to minimize walking distance, but more remote
locations saved labor on building fences against roaming
domestic animals. Clearing the secondary growth, rather
than a climax forest, was the preferred choice; only 1 out
of 381 Tsembaga gardens was in virgin forest. Men did
the heaviest tasks (tree felling, pollarding, fencing), and
women carried a disproportionate share of repetitive
chores (weeding and harvesting). But no form of food
production is governed by maximization of energy
returns. Nutritional imperatives are clear: legumes give
superior energy return compared to cereals but are less
palatable, and that is why wheat or rice are the staples.
Rappaport (1968) showed that the energy to grow pig
feed was often greater than the food energy of pork, but
how else could starchy roots be turned into food with
27% fat and 11% protein? Simplistic comparisons of en-
ergy returns find little or no value in such practices, but
the widespread human desire for fatty and meaty meals
justifies them.
6.2 Permanent Cropping
All traditional Old World agricultures shared the same
energetic foundations. They were powered by photosyn-
thetic conversion of solar radiation that produced food
