Environmental Engineering Reference
In-Depth Information
decades. In addition to the dangers of Bt contamination and rising pesticide resistance
among insects, there is one other way in which US corn production can impact biodiversity
within the USA. The long-term expansion of cultivated area in the USA has reduced the
area of grasslands and wetlands, while the growth in average farm size has eliminated many
fi
eld edges that have been important habitats for birds and other species (Runge, 2002).
While proponents of biotechnology argue that increased yields from transgenic crops will
reduce the need for cultivated land, this is an oversimpli
cation: higher yields will not auto-
matically lead to the return of existing cropland to wild habitat (Batie and Ervin, 2001).
While corn production has not expanded during this period, access to the Mexican
market has allowed the USA to keep corn land in production when it would otherwise
have been turned over to other crops. Increased exports to Mexico due to trade liberal-
ization - the threefold increase recorded since NAFTA - represent 1.3 percent of total US
production and should therefore be considered responsible for 1.3 percent of the envi-
ronmental impacts of corn production. Given the scale of US production, these are con-
siderable, representing, for example, 100 000 additional tons of nitrogen, phosphorous
and potassium-based loadings to US water each year. These externalized environmental
costs are not re
fi
fl
ected in US corn prices.
Mexico environmental impacts
In Mexico corn production accounts for over two-thirds of the gross value of agricultural
production. Corn covers half of the total area under cultivation for all crops (Sistema
Dinámico de Información y Análisis Agroalimentanó, DIAGRO). Roughly 3 million
people are employed in the cultivation of corn, more than 40 percent of the labor force
involved in agriculture or about 8 percent of Mexico's total labor force (Nadal, 2000). This
supports some 18 million people.
Mexico has the world's second highest annual per capita corn consumption (127 kg)
after Malawi (Morris, 1998). The pattern of consumption in Mexico is distinct from that
in the USA and other industrial countries since 68 percent of all corn is directly used as
food. In the world as a whole, just 21 percent of total corn production is consumed as
food. In industrial countries, including the USA, corn is more often used as livestock feed
or as an industrial input - a trend that is recently beginning to appear in Mexico.
In Mexico maize is the basic staple food for human consumption. One study found that
on average about 59 percent of human energy intake and 39 percent of protein intake was
provided by maize grain in the form of 'tortilla' (cooked corn dough) (Bourges and
Lehrer, 2004, in Turrent-Fernandez et al.,1997). Five thousand years of maize domesti-
cation has generated more than 40 races of maize specialized for direct human consump-
tion. By contrast, in the last hundred years, the industrialized countries have specialized
in developing hybrid varieties of maize for animal consumption and industrial use
(CIMMYT, 2001).
Mexico is the ancestral home of maize, and possesses a unique and irreplaceable genetic
diversity of varieties. Most of the country's maize production comes from traditional lan-
draces cultivated by peasant farmers from seeds that they preserve from their own crops
and from the exchange of seeds with neighbors in their communities (Wilkes, et al., 1981;
Serratos-Hernandez et al., 2001). Such
in situ
conservation of maize genetic resources is
considered essential to the long-term security of this important food crop, which has
particular economic value because it serves as the basis for crop breeding (Brush, 2000).
