The "Sustainable Agriculture" practice of taking a legume cover crop and incorporating into the soil, as shown in the above photo, adds nitrogen and organic matter to the soil, keeping it alive and healthy.

With the advent of synthetic fertilizers, however, farmers could short-circuit this and other organic practices that help maintain healthy soil. Because only a fraction of the synthetic fertilizers farmers put on their fields are utilized by crops, the excess volatizes into the air, contributing to acid rain and global warming, or travels off farms, washing down through the soil profile into aquifers and neighboring streams and rivers.

For example, in Des Moines, Iowa, a blue baby alert is issued whenever the synthetic fertilizer runoff from surrounding farmland is heavy. It is a warning to parents not to give tap water to children because nitrates in water bind to hemoglobin in blood and block the distribution of oxygen to the brain. Excess nitrates from the surrounding areas also move downstream, into the Mississippi River and into the Gulf of Mexico, where they form a "hypoxic" or dead zone as big as the state of New Jersey. They poison the marine world, stimulate the wild growth of algae and consume oxygen, which smothers fish.

There are biological tools, though, that can decrease the need for synthetic fertilizers on farms. To learn more about how the chemical fertilizer industry got its start when bomb-making factories switched over to making synthetic fertilizers at the end of WW II, and how replacing them with biological microorganisms can revitalize soils, read the first of three articles on Bombs, Beans and Dirt in the May/June issue of Touch the Soil magazine.