But there's more. In converting acreage to corn, American farmers are moving away from other major crops, like soy, which has the benefit of fixing nitrogen in the soil. Corn, by contrast, demands copious amounts of nitrogen fertilizer, which has a tendency to run off into streams and rivers, triggering oxygen-depleted dead zones, like the one which forms annually in the Gulf of Mexico. Experts fear that the corn boom will greatly exacerbate the problem.
It's not inevitable, however. As this item in American Agriculturalist notes, the 2007 Farm Bill offers an opportunity to encourage farmers to exercise "greater precision in fertilizer use, wetlands restoration, production of perennial crops such as switchgrass, and other conservation innovations." The item also notes that, "While Corn Belt watersheds account for less than nine percent of the land that drains into the Mississippi, land in these watersheds contribute about one-third of the nitrogen reaching the Gulf." A smart policy would focus efforts there.