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Minnesota Agriculture Department releases fertilizer restriction map

ST. PAUL — The Minnesota Department of Agriculture on Wednesday, Jan. 15, released a map meant to help farmers comply with a new rule intended to prevent groundwater contamination.

Called the Groundwater Protection Rule, the rule will affect agricultural producers in parts of the state whose soil and rock composition is particularly vulnerable to nitrate leaching. A chemical compound found in fertilizer and manure, nitrate can wash away from crop fields in the rain or because of irrigation and has been linked to cancer and other forms of illness.

Beginning in September, the new rule will restrict the extent to which farmers can spread fertilizer or manure in the fall or on frozen soil. The interactive map of the areas subject to the rule shows that portions of central and southeast Minnesota will have to comply. It also allows users to enter their own addresses to check if they will be required to abide by the rule.

Also affected will be parts of the state where the level of nitrate observed in groundwater measures 5.4 milligrams per liter or higher.

Under the federal law, drinking water that contains more than 10 milligrams of nitrate per liter is considered to be unsafe for human consumption. Some research has suggested that even lower thresholds may be linked to a higher risk of cancer or other illness.

A report released Tuesday by the Environmental Working Group, an environmentalist nonprofit, found that thousands of Minnesotans are drinking from water sources contaminated with potentially unsafe levels of nitrate.

A previous version of this story contained an error, stating that the Minnesota Department of Health released the map.