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A corn field

Fertilizer used to produce high-yield corn often has damaging environmental consequences.

U farm fertilizer recommendations could help environment

By Julie Reuvers

April 4, 2006

It's nearly planting time, and corn farmers and Minnesota lakes and rivers stand to benefit from new fertilizer recommendations outlined in a study by University of Minnesota soil scientists.

The University has developed a unique cost-benefit model based on the price of corn and of nitrogen fertilizer to help farmers determine the optimum amount of fertilizer to apply to maximize yields while minimizing runoff. The U research report, Fertilizing Corn in Minnesota, shows that using less nitrogen-based fertilizer can actually improve a grower's bottom line. According to this year's USDA survey of farmer's planting intentions, growers nationwide are planting less corn than usual, in part because of the high cost of fertilizer.

Many farmers rely on an old but widely accepted rule of thumb from the 1960s: apply 1.2 pounds of nitrogen fertilizer per bushel of corn expected. It was believed this formula would help a grower reach his or her yield goal, which was appropriate for the time, and it caught on across the Corn Belt.

"Excess nitrogen fertilizer can be lost by drainage into streams, ending up in the Minnesota River, the Mississippi River and eventually, the Gulf of Mexico," says Randall. "And it also leaches down into the groundwater aquifers, where people obtain their drinking water."

"But many of our experiments in Minnesota soils showed that between 0.7 and 0.9 (pounds of nitrogen per bushel) was working for many situations," says Gyles Randall, a University soil scientist, of his and his colleagues work in the University of Minnesota Extension Service. "The rates being applied using the 1.2 factor were pretty liberal. When fertilizer was cheap, it didn't make that much difference to a farmer's bottom line. Now that nitrogen is much more expensive, growers want to apply closer to the correct amount to save money and optimize profit."

And less nitrogen fertilizer runoff means less chance of it reaching one of the state's most valuable resources--groundwater aquifers--according to Randall.

"Excess nitrogen fertilizer can be lost by drainage into streams, ending up in the Minnesota River, the Mississippi River and eventually, the Gulf of Mexico," says Randall. "And it also leaches down into the groundwater aquifers, where people obtain their drinking water."

Randall notes that groundwater quality is most affected in the parts of the state with sandier soils, such as parts of Dakota, Anoka, and Sherburne counties. In those areas, groundwater aquifers are shallow and more vulnerable to leaching.

The journey toward the U's new, lower nitrogen recommendations began with scientists recognizing the need to standardize nitrogen fertilizer use among states. When watersheds cross state lines, it was discovered that despite the same crops and similar soils, each state had a different approach to developing nitrogen recommendations.

"Iowa had one set (of recommendations) and Minnesota had another set, yet they were farming side by side in the same watershed," Randall says. "That raised primary concerns. We knew we had a problem that needed to be corrected."

The new recommendations take into account a grower's tolerance for risk, type of soil, and specific crop rotations on the land to be farmed.