The International Consortium on Agricultural Biotechnology Research (ICABR)


Do Glyphosate-Resistant Soybeans Reduce Herbicide Use and Toxicity?
Evidence from the US Midwest

Gerald C. Nelson
University of Illinois,
Urbana-Champaign, IL

The most widely grown agricultural genetically modified organism (GMO) is glyphosate-resistant (GR) soybeans. Glyphosate (trade name Roundup) is a broad-spectrum herbicide, killing almost all vegetation to which it is applied. Glyphosate can be applied directly to fields planted to glyphosate-resistant soybeans. Competing plants that are not resistant are killed.

GR soybeans is an example of an input-substituting technology. With use of this crop it is possible to substitute glyphosate for other herbicides and management inputs. The choice of technique depends on the relative cost of inputs used. GR soybeans will only be profitable, and hence used, if they lower production cost. Bullock, assessed this choice of technique question for 1200 farms in the U.S. Midwest. They combined farm-specific information on weed problems with cost of production data for different soybean production techniques. Comparing 1997 profit-maximizing production practices with and without GR soybeans on these farms, they found that cropping systems involving GR soybeans had lower costs of marketed inputs (ignoring management savings) on 29 percent of the farms.

Glyphosate has several desirable environmental characteristics (Nelson, et. al). It degrades relatively quickly when exposed to heat and light. It is not water-soluble and so is much less likely to end up in groundwater than herbicides that are water-soluble (such as atrazine). The U.S. Environmental Protection Agency has given glyphosate its lowest toxicity rating. Some proponents of GR crops have argued that they have positive environmental effects by reducing the volume, toxicity, and/or offsite effects of herbicides used. But this potential for a positive effect depends on a comparison of environmental effects of cropping practices with and without the use of GR technology.

In this study we will assess the effect of the availability of GR soybeans on herbicide use on the sample of 1200 farms in the Midwest used by Bullock, et. al. Using a modified version of the Herbicide Selector software program developed at Ohio State University we will determine the cost-minimizing cropping practice on each farm, and the volume of active ingredient of each herbicide used for cropping systems with and without the use of GR technology. We will use a variety of toxicity measures to identify the effect of the technology on herbicide toxity. And because the data are georeferenced, we can indicate the spatial distribution of any herbicide use reduction.

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