Scientific American: When the heavy rains came to Iowa this spring, corn farmer Dave Miller tilled the rolling portions of his 255-hectare plot. Cutting into the soil slows runoff and, particularly, prevents water from gouging big gullies in the fertile but softly held land. A few years back such tilling would have cost him money, thanks to an attempt to pair farmers improving the carbon management of their soils and companies looking to reduce pollution. "We know that raising soil organic matter is good for soil, good...