Discussions on the environmental benefits (or costs) of genetically engineered crops tend to focus on relative volumes and toxicities of herbicides applied, effects of Bt, and possibilities of cross pollinating native plants. In so doing, what is often missed is an important environmental benefit of herbicide resistant crops. In particular, if a farmer can control weeds by spraying the entire field with a herbicide like glyphosate, that means they don't have to use other methods of weed control (like plowing) that may lead to soil runoff.
A new paper just released by the American Journal of Agricultural Economics by Edward Perry, GianCarlo Moschini, and David Hennessy tackles this issue. Here's a portion of the abstract:
“We find that glyphosate tolerant soybeans and conservation tillage are complementary practices. In addition, our estimation shows that farm operation scale promotes the adoption of both conservation tillage and glyphosate tolerant seed, and that all of higher fuel prices, more droughty conditions, and soil erodibility increase use of conservation tillage. We apply our results to simulate annual adoption rates for both conservation tillage and no-tillage in a scenario without glyphosate tolerant soybeans available as a choice. We find that the adoption of conservation tillage and no-tillage have been about 10% and 20% higher, respectively, due to the advent of glyphosate tolerant soybeans.”
It should be noted that herbicide tolerance isn't unique to biotechnology. There are several "non GM" crops on the market that are tolerant to certain herbicides but are not genetically engineered, at least as the term normally used.