Environmental Engineering Reference
In-Depth Information
the average availability of animal foodstuffs. Modern
farming increased the number of people supportable by
cultivating 1 ha to about four, but with the overwhelm-
ingly meatless diets of the early 1900s the average hect-
are of farmland could support at least six people, a
density traditionally achieved only by intensive farming
in Egypt or China.
The best modern performances are much higher.
China's post-1978 farming reforms, supported by what
are some of the world's highest fertilization rates, fed
about 8.5 people per hectare, and in the most populous
provinces the rate is in excess of 15 people per hectare.
The average Chinese diet still has less animal protein
than the Western one, but by the year 2000 its total en-
ergy content became the same as the mean in affluent Ja-
pan (Smil 2004a). National means of food availability at
retail level are published annually by FAO in the form of
food balance sheets (FAO 2006). Domestic production
of crops and animal foods is adjusted for net imports;
changes in stocks; harvests used for seed and industrial
conversions, fed to livestock, and wasted during storage;
processing; and transportation. Specific national details
are available for less than half of all member nations, and
many balances are calculated by FAO in Rome on the ba-
sis of numerous assumptions. Daily per capita availabil-
ities are in excess of 15 MJ/day in the United States
and many European countries and below 8.5 MJ/day
in parts of sub-Saharan Africa. Remarkably, by the year
2000, Chinese and Japanese supplies became virtually
identical in overall energy terms (nearly 12.5 MJ/day).
Only costly (and hence increasingly rare) household
food consumption surveys can accurately establish actual
daily food intakes. More common but less reliable esti-
mates based on income and expenditure surveys or on
24-h dietary recall
food supply and intakes in all affluent countries (Smil
2000b). The most representative U.S. surveys indicate
average daily adult male intakes of 10.3 MJ/day, adult
female intakes of 6.9 MJ/day, and a mean for all individ-
uals of all ages of 8.4 MJ/day (USDA 2006). There are
three reasons why this mean is below the average daily
requirement of about 9 MJ/day: the requirement mean
is too high given today's largely sedentary lifestyles; wide-
spread dieting among American females depresses the
overall intake mean; and (most likely), the actual intakes
(based on recall) are substantially underreported. This
implies a nearly 50% gap between average consumption
and average availability (15.7 MJ/day in 2003), and sim-
ilarly large food losses are true for many European coun-
tries. FAO uses the food balance sheets to estimate the
numbers of undernourished people. The total of 852
million in 2001-2002, with 815 million in poor coun-
tries, 220 million in India (FAO 2005b), is due over-
whelmingly to internal conflicts, distribution inequalities,
and poor agricultural management, not to physical short-
ages of food or to inability to produce sufficient amounts.
Increased productivities have thus been a universal
mark of subsidized farming, but these higher yields are
not due to higher net CO
2
assimilation. A rise in harvest
indices from 25%-30% in traditional cultivars to as
much as 50%-55% in improved varieties, that is, a redis-
tribution of the fixed C through breeding supported by
energy subsidies, has been responsible for the gains (Gif-
ford et al. 1984; Smil 2000b). Further gains are possible,
but comparisons of record yields with national averages
are not a realistic indicator. In fact, staple grain yields
have shown signs of leveling off, and environmental
stresses will always limit the gains.
From a social point of view, the sharply decreased la-
bor requirements of subsidized agriculture have been no
indicate large differences between
