The Minnesota Department of Agriculture provides a map showing six-inch soil temperature at 25 locations throughout the state.

The map, located at app.gisdata.mn.gov/mda-soiltemp/, is intended to help farmers and commercial applicators know where fall nitrogen fertilizer applications are restricted.

Under the MDA’s Groundwater Protection Rule, fall nitrogen fertilizer application is prohibited in vulnerable areas. In other areas, farmers are encouraged to wait for cooler conditions, delaying fall application of anhydrous ammonia and urea fertilizer, as well as manure, until the average soil temperatures reach 50 degrees Fahrenheit or cooler. This helps prevent nitrogen loss, protect water quality and ensure more nitrogen will be available for next season’s crop.

At cooler temperatures, nitrogen fertilizer is less likely to be converted to water-soluble nitrate. This is because microbes in the soil that convert ammonium to nitrate are less active in cooler temperatures, meaning more ammonium will remain in the soil. Once ammonium is converted to nitrate, it can be leached away by water percolating through the soil.

The soil temperature network may also help those applying manure in the fall. University of Minnesota Extension recommends the same temperature delay (6-inch soil temperature below 50 degrees F) to prevent leaching losses. Research from the University of Minnesota showed liquid dairy and hog manure injected in November produced yields 10 bushels per acre higher than manure injected in September and October.

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