Fine-tuning N applications is a good bet, economically and environmentally.Two summers ago, the worst Midwestern drought in a century shrank the Gulf of Mexico dead zone to one of the smallest in at least 50 years, due to reduced N runoff. But by May 2013, heavy Upper Midwest spring rains had delivered an estimated 153,000 metric tons of nutrients to the Gulf, nearly twice the previous year's level, according to National Oceanic and Atmospheric Administration data.By August, the dead zone had doubled in size, to 5,800 squaremiles, from 2012, according to U.S. Geological Survey estimates.
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