ST. PAUL — The Minnesota Department of Agriculture plans to test 70,000 private wells in the state’s farming regions to measure nitrogen that seeps into the ground after fertilizing.

The state said the level of pollution from tons of fertilizer that’s applied each year across the southern two-thirds of the state is rising. A survey in 2011 found excessive pollution in 62 percent of the wells monitored by the state in central Minnesota.

Besides the well testing, the state hopes to persuade farmers to better control their use of fertilizer. That could include asking farmers not to fertilize in the fall when the risk to groundwater is greatest, or even taking land out of production.

Environmentalists don’t think the plan is strong enough. Critics say it assumes landowners will voluntarily protect the water.