Herbicide-tolerant crops have encouraged farmers to practice no-till farming. In conventional farming, the fields are plowed ("tilled") to control weeds. Because of the superior weed control from GM crops, farmers now have to till much less often. This has led to improved soil health and water retention, reduced runoff, and reduced greenhouse gas emissions from agriculture. (National Academy of Sciences, Impact of Genetically Engineered Crops on Farm Sustainability in the United States, 2010) http://www.nap.edu/catalog.php?record_id=12804
Insect-resistant crops have greatly reduced the amount of insecticide that has to be applied to insect-protected crops. It’s estimated that an astounding 600 million pounds LESS active ingredient of insecticide has been used in the United States because of the use of GM crops, significantly reducing farmers’ costs and environmental footprint. (Brookes and Barfoot, Key environmental impacts of global GM crop use 1996-2011, in GM Crops and Food, 4/26/2013) http://www.pgeconomics.co.uk/pdf/2013globalimpactstudyfinalreport.pdf)
In developing countries, the increased production from GM seeds has allowed small farmers to generate more income off of the same amount of land, thus reducing the practice of cutting down forest for more cropland.
The greatest gains are yet to come. GM plants with more efficient use of nitrogen and other important nutrients mean less fertilizer will be needed, saving farmers money, and less fertilizer ends up in the environment. As mentioned previously, GM plants are available to withstand moderate water deficits. In the near future these same traits may allow the same yields or better while consuming less water. Such technologies have been demonstrated as effective in the laboratory and in field contexts.
Going forward, as we apply what we learning about organic, low-input and sustainable production practices to GM crops, we’ll see comparable or improved performance with less cost and environmental impact.