The Groundwater Protection Rule is based on the Minnesota Nitrogen Fertilizer Management Plan (NFMP) which recommends steps for the prevention and minimization of the impacts of nitrogen fertilizer on groundwater, and emphasizes involving the local agricultural community in problem-solving for local groundwater concerns. A map showing which areas are subject to restrictions on fall application and application to frozen soil is also available.

The Groundwater Protection Rule is based on the Minnesota Nitrogen Fertilizer Management Plan. The NFMP outlines the state strategy for preventing contamination and responding to elevated nitrate from fertilizer in groundwater. The rule restricts fall application of nitrogen fertilizer in areas vulnerable to contamination and outlines steps to reduce the severity of the problem in areas where nitrate in public water supply wells is already elevated.

Nitrate is one of the most common contaminants in Minnesota’s groundwater. The majority of Minnesota households have access to safe drinking water supplies. However, in areas vulnerable to groundwater contamination, some public and private wells have nitrate levels that exceed the health risk limit for nitrate. While elevated levels of nitrate in groundwater can result from several factors, a major contributor in rural Minnesota is nitrogen fertilizer that leaches past the crop root zone.

There is an extensive body of research documenting that nitrate from nitrogen fertilizer can leach below the root zone and migrate to groundwater. While contributions from soil organic matter, manure applications, and legume crops do occur, fertilizer inputs are recognized as the most important in terms of management options. Fertilizer as Source of Nitrate in Groundwater contains more information and a listing of relevant research articles and reports.

There are a number of reasons why the rule focuses on agricultural areas and not urban areas. First, only a small percentage of the nitrogen fertilizer sold in Minnesota is applied to lawns, golf courses and parks. The MDA estimates that 94 – 95% of the nitrogen sold is applied to agricultural crops. The rate of nitrogen application to lawns is only 25% of the rates normally used on corn and other high nitrogen using crops. Second, the fact that nitrate leaching from fertilizer applied to lawns can range from low to very low. Lawns are perennial and have a dense root structure, so nitrate leaching losses are very similar to agricultural perennial crops and native prairie. Third, most of the concerns related to lawns are related to phosphorus rather than nitrogen. Unneeded phosphorus inputs were drastically reduced (80 – 85%) when the MN Phosphorus Lawn Fertilizer Law was passed in 2005. As part of that law, it is illegal to apply any fertilizer on impervious surfaces. The Phosphorus Lawn Fertilizer Law greatly reduces the risk of nitrogen entering storm water and other surface water bodies.

Public water supply wells are monitored for water quality under the Safe Drinking Water Act administered by the Minnesota Department of Health (MDH). This data is used by the MDA and MDH to evaluate nitrate levels and water quality trends. The MDA may also install a local groundwater monitoring network in a Drinking Water Supply Management Area (DWSMA).

The purpose of the rule is to minimize potential sources of nitrate pollution in the state’s groundwater and to protect our drinking water. The rule is one tool, for specific situations, that is part of a larger strategy to reduce nitrate from fertilizer in groundwater.

The authority for the rule comes from the Minnesota Groundwater Protection Act, Minnesota Statute 103H. The MDA has the authority to issue administrative, civil, and criminal penalties against those who violate the rule under Minnesota Statute 18D.

The MDA held informal and formal comment periods, 17 listening sessions across the state and received more than 800 written comments.  The Groundwater Protection Rule became law in June, 2019. Application restrictions are posted  on the MDA’s website by January 15 each year and the fall application restrictions begin September 1. See question 11 below for more detail on the fall and frozen soil restrictions.

There are two parts to the rule. Each part contains separate provisions. Depending on where you farm, you may be subject to one part of the rule, both parts, or neither part.

Part 1: You are subject to Part 1 of the rule if you farm in a vulnerable groundwater area or in a Drinking Water Supply Management Area (DWSMA) that has 5.4 mg/L or higher of nitrate. This means you cannot apply nitrogen fertilizer in the fall and on frozen soils in those areas.

Part 2: You are subject to Part 2 of the rule if you farm land in a DWSMA with elevated groundwater nitrate concentrations. These areas will be designated a mitigation level 1, 2, 3 or 4.

A vulnerable groundwater area is land where nitrate can move easily through soil and into groundwater. The criteria used to determine vulnerability include coarse textured soils, karst geology, or shallow bedrock. The USDA NRCS soils maps were used to determine coarse textured soils and shallow bedrock. Coarse textured soils are within 91 cm of the soil surface and soils with shallow bedrock in the soil profile are within 102 cm of the soil surface.

A Minnesota Department of Natural Resources Pollution Sensitivity of Near-Surface Materials Report was used to identify the locations of karst.

The application of nitrogen fertilizer in the fall and on frozen soils will be restricted in areas with vulnerable groundwater or DWSMAs that are at or exceed 5.4 mg/L nitrate-nitrogen. An area with vulnerable groundwater is an area where nitrate can move easily through soil and into groundwater.

The criteria used to determine vulnerability include coarse textured soils, karst geology, or shallow bedrock. View the interactive Vulnerable Groundwater Area Map to see where application of nitrogen fertilizer will be restricted. Vulnerable quarter sections are shown in purple and DWSMAs are in green on the map.

In areas where 50% or more of the quarter section has vulnerable groundwater or is in a DWSMA, with high nitrate, applications of nitrogen in the fall and on frozen soils will not be allowed in the entire quarter section. If less than 50% of the quarter section has vulnerable groundwater, the restrictions do not apply.


Yes, fall application of nitrogen fertilizer will be allowed in vulnerable groundwater areas or DWSMAs with high nitrate concentrations in wells, in the following situations*:

  • to establish winter grains planted in the fall;
  • for fall pasture fertilization;
  • for perennial crops;
  • for grass seed production;
  • for cultivated wild rice;
  • for research on fields 20 acres or less in size, or
  • for growing fall cover crops within a potato rotation

*Must follow University of Minnesota nitrogen rate guidelines for each of the above.

There are additional exceptions and exemptions related to: soils with ultra-low permeability referenced in the rule; in areas with reduced leaching potential combined with a short spring planting season; and in counties where cropland makes up less than 3% of the total land area.

Ammoniated polyphosphate (MAP and DAP) and micronutrient formulations containing nitrogen can be applied as long as the applied rate does not exceed an average of 40 pounds of nitrogen per acre in a field. Fields with low or very low phosphorus levels, as determined by a certified lab, are exempt from this restriction.

Fall nitrogen fertilizer applications will also be allowed for agricultural research and demonstrations for academic purposes, provided the area is limited to 20 acres or less, or approved by the Commissioner of Agriculture.

These restrictions begin September 1, 2020.

Mitigation is the action of reducing the severity of a problem. In addressing the problem of nitrate contamination, mitigation levels will be based on nitrate data collected from public wells.

The MDA determines the mitigation levels for the DWSMAs of community supply wells based on monitoring data provided by the Minnesota Department of Health. All areas identified with elevated nitrate begin in a voluntary Mitigation Level (Level 1 or 2), unless the MDA determines there is a point source causing the well to exceed these levels or the MDA delays the determination of a mitigation level decision for good cause. A delay for good cause would allow MDA to collect additional information such as to evaluate a potential point source that may be a significant source of nitrate in the public well. 

The process for determining the mitigation level includes conducting a review of the quality of the monitoring data, the condition and vulnerability of the well, the hydrogeology and groundwater flow paths for groundwater flowing into the well, and potential point sources such as an agricultural chemical facility, septic system(s), feedlot(s) or a poorly constructed well that may be contributing significantly to nitrate levels in the well. View the current list of Mitigation Level Determinations.

Level One
Community public water supply wells (and their DWSMAs) with monitoring results of 5.4 to less than 8 mg/L nitrate-nitrogen fall under Level 1. At this mitigation level the MDA will encourage the voluntary adoption of the University of Minnesota nitrogen fertilizer BMPs and other practices which can reduce nitrate levels in groundwater such as precision agriculture, perennial crops, forages, cover crops, nitrification inhibitors, new hybrids, or taking targeted land out of production. These other practices are collectively referred to as alternative management tools or AMTs. Approved AMTs may substitute for nitrogen fertilizer BMPs.

DWSMAs at mitigation Level 1 are subject to Part 1 of the rule but are not subject to Part 2 of the rule.

Level Two
Community public water supply wells (and their DWSMAs) with monitoring results at or exceeding 8.0 mg/L nitrate- at any point during the previous 10 years, or projected to exceed the drinking water standard of 10 mg/L nitrate-nitrogen in the next ten years, will be included in Level 2.

For DWSMAs at Level 2, the MDA will work with local farmers to adopt practices that can reduce nitrate levels in groundwater. A local advisory team will be formed to include local farmers, agronomists, and others to help recommend the BMPs and AMTs that should be used. In addition, a local groundwater monitoring well network may be developed. The MDA will promote the implementation of appropriate nitrogen fertilizer BMPs and AMTs. To help facilitate AMT implementation, the MDA has worked with other agencies to make DWSMAs with elevated nitrate among the highest priority areas for state and federal funding. 

The MDA will conduct surveys to assess the adoption rates of BMPs and other practices and use computer modeling to estimate the change in nitrate losses over a DWSMA. The modeling will consider the soils, crops, agricultural practices and precipitation in the DWSMA and help local farmers estimate whether changes in practices will improve water quality.

Level Three
Level 3 is the first regulatory level. A Level 2 site will progress to Level 3 if one of the following occurs: after not less than 3 growing seasons or the estimated lag time, whichever is longer, the recommended BMPs are not adopted on 80% of the cropland acres (excluding soybean acres); or the nitrate concentrations in groundwater continue to increase; or, after not less than three growing seasons the residual soil nitrate below the root zone increases. The estimated lag time is the time it takes for changes in practices to have an effect on groundwater quality or on the public well with elevated nitrate. This time may vary significantly based on the local soils, hydrogeology and actual precipitation. Computer modeling and groundwater age estimates can be used to determine the estimated lag time. Residual soil nitrate testing below the root zone is a more difficult process of testing nitrate levels in soil. It is used to determine if nitrate is increasing or decreasing over time and may be used in locations with very long lag times.

The Commissioner of Agriculture – in consultation with a local advisory team – would then require landowners to implement actions such as BMPs, soil testing, record keeping, and educational programs. The Commissioner may delay moving to a regulatory level if computer modeling indicates that the adopted practices are going to be effective in reducing nitrate levels below 8 mg/L.

Level Four
Level 4 is the second regulatory level. If nitrate-nitrogen in the public water supply well exceeded 9 mg/L for any three samples in the previous 10 years; or after three years the residual soil nitrate below the root zone increases; or after three years or the estimated lag time, whichever is longer, the nitrate levels continue to increase, then the DWSMA would be given a Level 4 designation. The Commissioner of Agriculture – in consultation with a local advisory team – could require landowners to implement additional practices beyond best management practices. These practices would be determined on a site-specific basis following guidance outlined in MN Statutes Chapter 103H.275 Subd. 2(a). However, they shall not include restrictions on the primary crop or require fertilizer rates below the low end of the University of Minnesota recommended fertilizer rate range.

DWSMAs will be monitored and will move up or down a mitigation level according to changes in water quality. DWSMAs may only move up one mitigation level at a time. For example, a DWSMA will never go from Level 1 to Level 3 in a single cycle.

The MDA has the authority to regulate nitrogen fertilizer; the Minnesota Pollution Control Agency (MPCA) has the authority to regulate manure.

The rule calls for following the nitrogen fertilizer BMPs. One of the BMPs is to properly credit all nitrogen sources, including manure, when determining the nitrogen fertilizer rate.

If the nitrogen fertilizer best management practices (BMPs) are implemented on more than 80% of the cropland in your area, and residual soil nitrate levels do not increase, or nitrate levels in the public water supply do not increase, then regulations will not be required. Otherwise the Drinking Water Supply Management Area (DWSMA) can move to a regulatory level.

In cropland areas with high nitrate concentrations in the groundwater, the MDA strongly encourages farmers to consider using Alternative Management Tools (AMTs). In the rule, Alternative Management Tools are defined as “specific practices and solutions approved by the commissioner to address groundwater nitrate problems.” Examples of AMTs include, but are not limited to, type of precision agriculture, nitrification inhibitor, cover crops, annual crops, and alfalfa. The MDA will maintain a published list of approved AMTs. This list will be updated on an annual basis. Under the Groundwater Protection rule, land with AMTs in place will be considered BMP compliant in the BMP survey.

Non-compliance with the Groundwater Protection Rule will generally first be addressed by providing compliance assistance to the landowner. Except for cases that involve human endangerment, the general progression of penalties involves 1) education, 2) compliance assistance, and 3) enforcement.

The MDA has the general authority to issue administrative, civil, and criminal penalties for violations of its rules through Minnesota Statutes 18D. Penalty actions are based on the severity of the violation and the facts of the case. The MDA takes a progressive enforcement approach, meaning that repeat violations will be met with stronger penalties than first violations.

The only parties possibly subject to penalties would be those in violation of the fall/frozen soil nitrogen fertilizer application restriction and those who violate a Commissioner’s order for mitigation Level 3 and Level 4. If a regulated party disagrees with a proposed penalty, the party will have the opportunity to challenge it.

Definition and interpretation of Responsible Party

The Responsible Party is the owner, operator or agent in charge of cropland. This means the person who decided to apply the nitrogen input will be identified as the Responsible Party. The MDA responds and investigates written complaints of nitrogen application after Sept 1 in a Drinking Water Supply Management Area (DWSMA) with elevated nitrate, a vulnerable groundwater area or on frozen soils in these areas. Facts and information obtained from the investigation will be used by the MDA to determine the responsible party. 

In an effort to provide the best customer service possible, the MDA strongly recommends if you or your company is contracted by a grower / agent in charge of cropland, that you review the MDA’s  groundwater vulnerability map PRIOR to agreeing to any nitrogen applications after September 1.  If the application site is in a DWSMA on the MDA’s map, in a vulnerable groundwater area or on frozen soils in a vulnerable groundwater area, notifying the customer of this will enable the customer to comply with Minnesota’s Groundwater Protection Rule.

The vulnerable soils map and complaint form are provided to you for your reference:  vulnerable soils map and the nitrogen fertilizer application complaint form.