The Minnesota Department of Agriculture wants to test 70,000 private wells throughout the state’s farming regions as part of an ambitious but controversial plan to measure and fix nitrogen contamination in drinking water.

The initiative reflects urgent concerns about Minnesota’s groundwater, which in some areas shows rising levels of pollution from the tons of fertilizer and other forms of nitrogen applied each year across the southern two-thirds of the state. A 2011 survey found that 62 percent of the monitoring wells in central Minnesota, where groundwater is most susceptible, showed excessive contamination.

The plan, which officials hope to complete early next year, also calls for persuading farmers to ratchet up their control of fertilizer. That could mean asking farmers not to fertilize in the fall, when the risk to water is greatest — or, potentially, stronger steps such as requiring farmers to plant different crops or paying them to take land out of production altogether.

Agriculture Department officials say the plan reflects everything they’ve learned about managing fertilizer since they were assigned responsibility for protecting the state’s groundwater a quarter-century ago. So far they have relied on voluntary measures, but now for the first time are inching toward direct regulation when nothing else works.

But environmental advocates, state health officials and at least one influential legislator say the plan is inadequate. They are urging the department to adopt tougher measures to address an increasingly widespread contaminant that can be lethal to infants and harmful to livestock.

The sharpest critics say the new plan perpetuates a failed strategy that relies on trusting that landowners will voluntarily protect water, and that the agency is not fulfilling its charge to protect groundwater that provides drinking water to three-fourths of the state.

“It’s more of the same with the public’s money,” said Rep. Rick Hansen, DFL-South St. Paul. “I don’t think that’s what the law says and that’s not what Minnesotans expect.”

First plan surfaced in 1990

The Agriculture Department devised its first fertilizer-management plan in 1990, recognizing that groundwater contamination was becoming a significant problem in central, southwest and southeast Minnesota. Since then, the state, the University of Minnesota and other agronomists have devised increasingly sophisticated practices to minimize nitrogen losses — which farmers largely follow, officials said.

At the same time, technological advances now provide farmers exquisitely precise information on just how much fertilizer to apply. As a result, nitrogen use per bushel of corn has dropped sharply.

Still, the number of acres devoted to corn has risen, and so have fertilizer sales. Today an estimated 800,000 tons are applied every year, primarily on the more than 10,000 square miles devoted to corn and potatoes. Soybeans also naturally add nitrogen to the soil.

Drinking water contamination has risen, as well. Today 27 towns, from Ellsworth in southwest Minnesota to Lewiston in the southeast and Park Rapids in the north-central part of the state, have worrisome levels of nitrates, the contaminant derived from nitrogen, in their drinking water. Other towns, such as Hastings and St. Peter, have spent millions of dollars to install sophisticated water treatment equipment.

Since 1985, the Agriculture Department’s monitoring wells statewide have shown steadily rising concentrations of nitrates in most regions, some at levels that one leading environmental group called “startling.”

The new plan would start with a round of private well testing in areas known to have groundwater problems, with funding, officials hope, from the 2008 Legacy Amendment. If they find that 5 to 7 percent of the wells in an area are contaminated, they would create a local advisory group, including farmers, to recommend better practices.

But the plan says little about what would happen if that doesn’t work, said Faye Sleeper, co-director of the university’s Water Resources Center and a member of the department’s advisory panel. The state agriculture commissioner has authority to impose rules to protect groundwater, and, Sleeper said, it’s time to start thinking about how. “You need that in the toolbox to be effective,” she said. “You don’t use it often, but when you need it, it’s there.”

The voluntary restrictions would increase according to the number of contaminated wells. But the process could take three or four years, and extensive monitoring, which critics say would be too little too late. Randy Ellingboe, a manager at the Minnesota Department of Health, said that waiting until wells show nitrates at 7 parts per million might not give communities and homeowners enough time to avoid expensive treatments. He said he’d like to see a “more accelerated approach.”

Others were much harsher. Kris Sigford, water quality manager for the Minnesota Center for Environmental Advocacy, a nonprofit environmental law firm, said the new plan is weaker than the one established in 1990. “It’s like pretending the last 24 years never happened,’’ she said. “The state should implement the most stringent ... protection measures now where groundwater contamination is well documented,” she said.

And while the plan does not include cost estimates, Hansen said a potentially enormous expense would be borne by taxpayers instead of the farmers and landowners who profit from fertilizer. “It implicitly spends millions of dollars, and they may not achieve the outcome of preventing groundwater contamination,” he said.

Agriculture officials say relying on landowners to make the right choices will work. Pilot projects have proved that local communities and farmers “want to be part of the solution,” said Greg Buzicky, who headed development of the department’s plan.

“Water quality is an important issue for all of us in agriculture right now,” said Adam Birr, research director for the Minnesota Corn Growers Association.

The voluntary approach can work, Birr said, “when you get the right people at the table.”

Buzicky said agriculture officials will consider recommendations on how to change the plan, and then submit it to Agriculture Commissioner Dave Frederickson for final approval. In the meantime, they are already testing wells in some communities, including Dakota County, which has serious nitrate contamination in drinking water.

Public hearings on what they find will start in January.