Minnesota’s nitrogen fertilizer application restrictions begin this fall

Taylor Becker and Greg Klinger
University of Minnesota Extension

A little over a year ago, the Minnesota Agriculture Commissioner signed the Groundwater Protection Rule with the goal of minimizing potential sources of nitrate pollution to Minnesota groundwater.

One impact of this rule for farmers and agronomists is a restriction on the application of nitrogen fertilizer in the fall and on frozen soils in certain areas of the state starting Sept. 1. These areas are mostly in the north-central, southeast and southwest parts of the state, but also include smaller areas in other locations. Roughly the northern third of the state is excluded from restrictions on fall nitrogen fertilizer applications.

Question: Are all nitrogen-containing fertilizers banned from being applied in the fall in these areas?

Answer: No. There are specific exceptions that allow fall application of U of M recommended rates to establish winter grains or perennial crops, and when applying MAP, DAP or micronutrient formulations, up to a field-average rate of 40 lbs/acre nitrogen in the fall (roughly 200-400 lbs/acre of total product). The 40-pound rate does not apply to fields with “low” or “very low” soil test phosphorus values. More exceptions can be found on the Minnesota Department of Agriculture website.

Q: Is manure use in the fall restricted?

A: No, the fall nitrogen fertilizer use restrictions in place under this rule apply only to commercial nitrogen fertilizers.

Q: Under the Groundwater Protection Rule, are there other potential impacts farmers and agricultural professionals should be aware of?

A: Yes, but only if you farm within one of the green DWSMA areas on the map. The Groundwater Protection Rule includes additional considerations for nitrogen management practices in DWSMAs with the goal of preventing public water supply well nitrate levels from exceeding 10 mg/L. These include the promotion of nitrogen fertilizer best management practices (BMPs) — additional information can be found under Part 2 of the rule on the MDA website. Regulations that mandate nitrogen fertilizer best management practices (BMPs) or other practices are possible in these areas. However, these are long-term considerations directly tied to local water quality trends and how widely BMPs are being used.

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