New rule restricts nitrogen fertilizer application after Sept. 1

Beginning September 1, 2020, Part 1 of the Groundwater Protection Rule goes into effect across Minnesota, restricting the application of nitrogen fertilizer in the fall and on frozen soils in areas with vulnerable groundwater. It applies to approximately 12-13% of Minnesota’s cropland and nearly half of the land in Washington County.

This video from Minnesota Department of Agriculture explains the new Groundwater Protection Rule.

The Minnesota Department of Agriculture (MDA) developed the Groundwater Protection Rule in collaboration with farmers, agronomists, and local government in order to reduce nitrate contamination across the state. The Minnesota Pollution Control Agency has found that 3 billion pounds of nitrogen enter our water supply from fertilizer and nutrient-rich soil every year. The amount of nitrogen flowing downstream into the Mississippi River has doubled since 1996 and in some agricultural communities, more than 20% of wells are contaminated by nitrates.

Minnesota map showing pounds per acre per year of Nitrate getting into surface water. From MPCA.

In Washington County, 100% of our drinking water supply comes from groundwater. Six years ago, Washington Conservation District worked with MDA and local landowners to sample well water from homes in southern Washington County. Of the samples tested, 20.2% of those in Cottage Grove (50 total) and 8.3% of those in Denmark Twp. (16 total) had nitrate levels above the Health Risk Limit (10 mg/L).

The map above shows townships in Minnesota where Minnesota Department of Agriculture has tested private wells. The colors indicate the percentage of wells in each location that had nitrate levels above the allowable health standard.

The biggest risk associated with high nitrates in drinking water (at or above 10 mg/L) is a disorder called “blue-baby” syndrome, or methemoglobinemia. It affects infants younger than six months old that drink formula mixed with the water and can pose a risk to pregnant women as well. Blue-baby syndrome reduces the oxygen carrying capacity of blood and babies suffering from the illness might turn bluish in color, develop long-term digestive or respiratory problems, or even die.

Last year, the Washington Conservation District partnered with MDA to form a local advisory team in southern Washington County in order to develop strategies to address nitrates contamination. This year, the Conservation District received a $75,000 grant from the Minnesota Clean Water Fund to provide technical and financial assistance to agricultural landowners to promote nitrogen fertilizer best management practices, help to develop nutrient-management plans, and implement alternative land management tools including cover crops and perennial crops.

Cereal rye cover crop in corn stubble. Studies show that use of cereal rye reduces the amount of nitrogen entering drainage tile. Photo from

Currently, the Groundwater Protection Rule only applies to agricultural land – not lawns or golf courses. The Minnesota Department of Agriculture estimates that 94 – 95% of the nitrogen sold in our state is applied to agricultural crops. Previous research has also shown that nitrogen applied to lawns is less likely to leach into groundwater because turf grass is perennial and has a dense root structure. For the same reason, the Groundwater Protection Rule also has an exemption allowing farmers to apply fall fertilizer to perennial crops. 

To learn more about the Groundwater Protection Rule, find a map of areas where fertilizer restrictions apply, and learn about exceptions to the rules, go to

Washington Conservation District offers technical assistance and cost share/incentive payments to implement nitrogen fertilizer best management practices. For questions or to set up a site visit, please contact Angela Defenbaugh at or 651-330-8220 x23.