Know Where, When to Apply Fall Nitrogen Fertilizer

Reminder: restrictions go into effect September 1

St. Paul, MN - The Minnesota Department of Agriculture (MDA) reminds farmers and commercial applicators that fall nitrogen fertilizer applications are restricted in some areas of the state. Under the MDA’s Groundwater Protection Rule, fall nitrogen fertilizer application is prohibited in vulnerable areas of Minnesota based on environmental concerns or risks. Areas with coarse-textured soils, shallow soils to bedrock, or karst geology are the most vulnerable to nitrate-nitrogen loss and groundwater contamination.

The restrictions begin September 1 each year. Farmers are encouraged to check the online map before fall application to determine if their fields are subject to these restrictions. View a map of the vulnerable regions of the state (mda.state.mn.us/chemicals/fertilizers/nutrient-mgmt/nitrogenplan/mitigation/wrpr/wrprpart1/vulnerableareamap). For more information on the restrictions outlined in the Groundwater Protection Rule, visit mda.state.mn.us/nfr.

In other areas of the state where fall nitrogen fertilizer application is allowed, the MDA advises farmers and commercial applicators to check soil temperatures and wait until the average soil temperature reaches 50 degrees F or cooler before applying fertilizer. Research shows that delaying fall application of anhydrous ammonia and urea fertilizer, as well as manure, reduces nitrogen loss, protects water quality, and ensures more nitrogen will be available for next season’s crop.

To assist tracking soil temperature, the MDA provides access to real-time, 4- and 6-inch soil temperatures at 70 locations across the state. View the interactive map to find the current 6-inch soil temperature and the past week’s history (gis.mda.state.mn.us/mda-soiltemp/).

Although the soil temperature network was established to support application of nitrogen fertilizer, it is equally useful for those applying manure in the fall. University of Minnesota Extension recommends the same temperature delay (after soil temperature is below 50 degrees F) to prevent leaching losses.

For more information on the Six-inch Soil Temperature Network visit mda.state.mn.us/soiltemp.

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