Environmental Engineering Reference
In-Depth Information
Box 8.3
Predynastic Egypt: Population Density and Grain Farming
Excavations indicate that Egypt's predynastic settlements were about 2 km apart and
that they used only a quarter of the outer part of the 1.5-km-wide l oodplain for cul-
tivating grains, whose yield was about 600 kg/ha (Hassan 1984). This would prorate
to about 75 ha of farmland per settlement and an annual harvest of 45 t of grain. With
25% of the harvest reserved for seed and at least another 10% lost in storage, there
would be about 30 t of food grain (food energy density of 15 MJ/kg). Assuming (rather
liberally) average daily food requirements of 10 MJ per capita and 75%-85% of that
total supplied by staple cereals, that would be enough to feed about 150-170 people
(and up to 200, with slightly lower daily per capita needs).
But because the Nile's annual l uctuations could cut the long-term average yields
by as much as one-half, the minimum supportable population was perhaps no higher
than 75-85 people, or just 1-1.1 people/ha of cultivated land (or 100/km
2
). Egypt's
population density rose from 1.3 people/ha in 2500 BCE to 1.8 in 1250 BCE, to 2.4
by 150 BCE (Butzer 1976), and 2.7 Mha cultivated during the Roman rule produced
food for at least seven million people (one-third of them outside Egypt), with an implied
a population density of about 2.5 people/ha of arable land. After more than 1,500
years of decline, the average density rose to about 5 people/ha (500/km
2
) only after
1800.
annual l ood l ow; moreover, the absence of efi cient water-lifting devices restricted
irrigation to low-lying areas in the river's valley. As a result, there were no summer
crops, and the population density supportable by annual l ood soon reached its limit
(box 8.3).
Fragmentary Chinese information offers similar rates. Prior to the third century
BCE there was very little irrigation, double cropping, or crop rotation, and popula-
tion densities ranged from just 1 person/ha in the arid north to 2 people/ha in the
rice-growing south; they rose to about 2.8 people/ha during the early Ming dynasty
(1400 CE) and to 4.8 people/ha two centuries later during the early Qing dynasty
(Perkins 1969). By 1900 the mean was about 5 people/ha, Buck's (1937) detailed
rural surveys resulted in a highly accurate mean of 5.5 people/ha of cultivated land
around 1930, when many irrigated southern regions could support 7 people/ha
(700/km
2
).
Because corn (a C
4
species) is an inherently higher-yielding crop than wheat and
rice (both C
3
), the most fertile area of ancient Mesoamerica could support higher
population densities than in the Old World. The highest rates were achieved thanks
to the Aztec
chinampas
, rectangular i elds raised by using mud, crop residues, and
grasses and 1.5-1.8 m above the shallow waters of Lakes Texcoco, Xalco, and
