Minnesota's problem with nitrogen pollution is so big that current best practices are inadequate to deal with it, according to a new report from the Minnesota Pollution Control Agency.
The study shows that 158 million pounds of nitrogen leave the state in rivers every year, contributing to the dead zone in the Gulf of Mexico.
The state has no standards to protect aquatic life from the harmful effects of too much nitrogen, but 27 percent of Minnesota's rivers have nitrate levels that exceed federal and state drinking water standards.
Seventy-three percent of the nitrogen comes from crop land -- primarily running out of tile drainage systems and leaching into groundwater.
The most heavily-polluted part of the state is south central Minnesota, where corn is the major crop and tiling is extensive.
The report says if farmers optimized standard best management practices, they could reduce nitrogen pollution by up to 35 percent. The practices include applying fertilizer at the optimal time and in optimal amounts, planting perennials along streams, treating tile drainage waters, planting cover crops in the fall, and converting marginal land to perennial vegetation. But national groups working on the dead zone problem in the Gulf of Mexico say reductions closer to 45 percent are needed.
Several environmental groups hailed the report as an important step toward cleaner water. But Whitney Clark, executive director of Friends of the Mississippi River, said the report makes it clear than current approaches are not working.
"The state appears to have committed itself to the voluntary approach," he said, "and many of us have been arguing that we've tried voluntary approaches since the Great Depression, and current practices don't work."