The Minnesota Department of Agriculture (MDA) is reminding 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 due to environmental concerns or risks. Areas with coarse-textured soils or areas above fractured bedrock or karst geology are the most vulnerable to nitrate loss and groundwater contamination. View a map of the vulnerable regions of the state at www.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  www.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 for cooler conditions. Research shows that delaying fall application of anhydrous ammonia and urea fertilizer, as well as manure, until the average soil temperatures reach 50 degrees F or cooler helps prevent 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 real-time, six-inch soil temperatures at 25 locations across the state. In addition, the MDA provides links to soil temperature from the University of Minnesota research stations and the North Dakota Ag Weather Network (NDAWN) weather stations. View the interactive map to find the current six-inch soil temperature and the past week’s history at https://app.gisdata.mn.gov/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 (six-inch soil temperature below 50 degrees F) to prevent leaching losses. Research from the University of Minnesota showed liquid dairy and hog manures injected in November produced yields 10 bushels per acre higher than manures injected in September and October.

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