Agriculture Reference
In-Depth Information
facilitate the process of invasion by altering the mycorrhizal community in the soil over
time. Introgression of a
Bt
gene that had a negative impact on AMF (or any other group of
soil organisms) might be expected to have similar effects on the soil ecosystem, but this
remains to be seen.
It has been proposed that
Bt
crops could contribute to agricultural sustainability by reduc-
ing the amounts of chemical insecticides that are usually applied in conventional agri-
cultural systems, improving yield in areas where insect control measures are limited and
minimizing the negative effects to soil structure associated with tillage, as
Bt
genes are
often also stacked with HT traits. By contributing to reduced insecticide usage,
Bt
crops
could confer benefits to farmworkers and the environment, and because many
Bt
cultivars
also include herbicide tolerance traits, conservation tillage measures could be employed to
reduce the effects of tillage on soil organisms and help minimize loss of soil from erosion.
The potential environmental benefits of
Bt
crops may perhaps be best illustrated by
Bt
cot-
ton. Historically, 25% of all insecticides used in agriculture were applied to cotton—more
than to any other crop (James, 2010). By planting
Bt
cotton that contains its own insecticide
targeted against the cotton bollworm, the environment has been spared from pollution
with thousands of pounds of broad-spectrum insecticides each year. The EPA reported
that
Bt
cotton reduced insecticide use by nearly 1 million gallons in 1999 alone and saved
farmers nearly $500/acre in chemical costs. The high level of confidence that many farmers
have in this type of crop biotechnology is reflected in the large amount of land dedicated
to GM crop production in the United States: In 2010, 93% of the cotton crop and 86% of the
corn crop in the United States was genetically engineered (USDA, 2010).
Bt
corn has also
been shown to offer communal benefits; non-
Bt
plants grown in close proximity to
Bt
ields
also benefit from reduced pest damage through a “halo effect” on the target pest popula-
tion (Alstad and Andow, 1996; Hutchison et al., 2010). Moreover, because the
Bt
protein
expressed in crop plants has high specificity to certain insect groups (i.e., Lepidoptera,
Coleoptera), the Cry proteins are not likely to have direct toxic effects on nontarget organ-
isms (with a few exceptions). There is also the potential of increased yield of
Bt
crops
(when compared with crops without insect protection), which may help to reduce land
area required for agricultural production. It remains to be seen if this, indeed, will be the
case, however, as high-yielding crop varieties can also be developed through conventional
breeding methods, and the use of cultivars adapted to particular agricultural regions can
also improve yields.
The relatively rapid and widespread commercialization of transgenic crop technol-
ogy, however, has contributed to a certain level of mistrust and suspicion by the general
public, particularly in countries outside the United States. The public perception is that
GM crops are being rapidly adopted by farmers throughout the world without a complete
understanding of the long-term environmental impacts. Even in the United States, 100
times more resources are invested in developing transgenic crops than are spent on risk
assessment and monitoring for nontarget effects after their commercial release (Thies and
Devare, 2007). While
Bt
crops may help to improve the sustainability of conventional agri-
cultural systems by reducing insecticide usage, they may not be of benefit in agricultural
systems in which long-term sustainability is the goal (i.e., organic farming systems or low-
input farming systems) as they offer few, if any, benefits to enhancing soil fertility and may
even have negative effects on fungal symbionts that are essential for nutrient uptake in
low-input systems. Moreover, caution should be exercised when cultivating certain types
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