Two summers ago, the worst Midwestern drought  in a century reduced the Gulf of Mexico dead zone to one of the smallest in at least 50 years, due to reduced nitrogen 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 (NOAA data). By August, the dead zone had doubled in size to 5,800 square miles from 2012, according to U.S. Geological Survey estimates.

To many environmentalists, the numbers argue the need for regulatory restrictions on nitrogen. To Cliff Snyder, nitrogen director, International Plant Nutrition Institute (IPNI), it represents wasted resources economically and environmentally. With margins tight to nonexistent, the time may never be better to make needed changes. "We need to look at lost value at the farm gate and environmentally," he says.

Finding the win-win economic solution for growers and society is the goal behind long-term nitrogen studies at Purdue University and at the University of Minnesota's Southern Research and Outreach Center (SROC). Both express the same reality: Corn and soybean production are leaky systems. No system has yet been devised to produce complete utilization, nor is it likely. "No one system will work across the Corn Belt," says Jeff Vetsch, assistant scientist, SROC. "There is no easy answer or solution. "

Purdue University researchers have gathered eight years of data from field scale trials at more than 200 sites across Indiana. As in the 15-year Minnesota research effort, they emphasize understanding the Agronomic Optimum nitrogen Rate (AONR) and the Economic Optimum nitrogen Rates (EONR).

"Whenever corn prices drop and fertilizer doesn't follow as quickly, growers pay more attention to economically optimum rates,” says Bob Nielsen, Purdue Extension corn specialist and agronomy professor.

Of course, identifying the optimum rate lies in the conversion of ammonium and nitrates from organic matter through mineralization, rainfall and from applied inorganic fertilizer. Managing the process to get the greatest economic value from the investment at the lowest risk of loss and environmental degradation depends on soils, organic matter, rainfall distribution, temperature range, tillage and cropping management systems.

Even within a particular region or farm, agronomically optimal nitrogen rates can vary substantially. At a West Lafayette, Ind., site, the average is 184 pounds per acre. However, it has varied from 130 to 221 pounds per acre in individual years, depending on soil-N supply, fertilizer nitrogen loss and growing season weather.

Both the agronomic and economic optimum nitrogen rates can vary considerably depending on corn prices and nitrogen costs. In the matrix for northeast, east-central and central Indiana with a 217-pound agronomically optimum nitrogen rate, the EONR for $4 corn ranges from 206 pounds per acre at 20¢ per pound of N, down to 161 pounds per acre nitrogen at $1 per pound of N.