I wish there was an easy answer to your question, but I'm not sure there is. When I was kid growing up on my family's farm in western Kansas, we were restricted, as a matter of U.S. agricultural policy, to producing only wheat on a continuous basis. This created a number of management challenges. Specifically, we had some weed and disease issues that became a perpetual battle. I spent many long hours on a tractor, tilling the soil, in order to manage weeds.
Today, as a matter of U.S. agricultural policy, my father and brothers can and do plant a much more diverse rotation of crops, largely in response to the prices they can receive for those crops. In other words, they produce to meet the market demand signals that come from consumers. They are no longer restricted to planting wheat exclusively. While wheat is still an important crop on our farm, we plant soybeans, sorghum, corn and sunflowers in a rotation that helps to control weed, insect and disease cycles. Without the weed- and insect-control benefits attributable to GM crops, I'm not sure we would be planting this diverse rotation of crops where my family farms.
Over the past five to seven years, the demand for corn has been higher than the market could easily supply, leading to historically high expected output prices for corn. With the government no longer mandating the production of certain crops in certain areas, farmers in areas where corn production is a clear economic winner have turned to planting more corn and fewer rotational crops.
This leads to an interesting dilemma. Cropping the same crop year after year has declined in some areas while increasing in others as a function of market signals given by consumers to farmers. Most farmers I know would agree that planting more crops in a rotation is preferable, given the agronomic advantages, but few are willing to forgo large economic opportunities to do so.
Back to my family's farm: we no longer till the soil to control weeds. And we have been experimenting with cover crops as a way to improve soil quality. Roundup Ready crops have played an important role in allowing us to move toward “no tillage” practices on our farm, and there are studies that suggest that the benefits of improved weed management with Roundup Ready crop systems have been the most important factor for most farmers. Minimizing tillage reduces soil erosion and improves water infiltration, and, at the same time, reduces greenhouse gas emissions. Less tillage leaves more crop residues on the undisturbed soil to sequester carbon dioxide and reduces emissions associated with fuel used to make tillage trips across a field. Studies have shown that biotech crops have reduced GHG emissions by 23 billion kilograms of CO2 equivalent emissions in 2011 alone. This is equal to removing the GHG emissions burden of 10 million cars from the road for one year.
Finally, in one of the most important studies I have seen on the topic of agriculture and environmental impact, it was estimated that the yield improvements in agriculture in the latter half of the 20th century reduced GHG emissions by 590 gigatons of CO2 equivalents. The adoption of GM crop technology by farmers throughout the world has also contributed to yield improvement in many countries. Increasing productivity on approximately 11 percent of the earth's arable landmass, while protecting pastures, grasslands and forests, will help farmers provide adequate food for a growing global population. To ensure success, farmers need to utilize all of the available production practices and technologies to enable efficient and productive agricultural systems that protect the environment.