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The Minnesota Department of Agriculture (MDA) Six-Inch Soil Temperature Network provides real time soil temperatures at locations across Minnesota. The network was established to assist in following best management practices for fall nitrogen fertilizer application which refer to a soil temperature at a six-inch depth.

In areas of the state where fall nitrogen fertilizer application is appropriate, Minnesota's nitrogen fertilizer best management practices (BMPs) for nitrogen use recommend that fall application of urea (46-0-0) and anhydrous ammonia (82-0-0) be delayed until soil temperatures at a six-inch depth stabilize below 50 degrees F.

Ammonia (NH3) is one of the primary forms of nitrogen applied in the fall. It reacts immediately upon contact with soil water to form ammonium which binds tightly to the soil. If average soil temperatures are above 50 degrees F soil microbes can transform ammonium into nitrite, and then into nitrate. The nitrate form is highly mobile with water and can leach from the soil. This results in less available nitrogen for crops in the following growing season. The leached nitrate can travel to groundwater and cause an increase in nitrate levels. Nitrate levels exceeding 10 mg/L are above Minnesota's drinking water standard and unfortunately these levels are being found in well water in several areas of the state. 

The MDA is responsible for the development, promotion and evaluation of BMPs for pesticide and nitrogen fertilizer use. The Six-Inch Soil Temperature Network is part of meeting that responsibility. It is a cooperative effort between the Minnesota Department of Natural Resources (DNR) and the MDA. All of the current Six-Inch Soil Temperature Network sites are co-located at DNR cooperative stream gauging sites. MDA soil temperature measuring probes are connected to DNR data logging systems. Soil temperature information is collected by DNR data logging equipment every 15 minutes and up-linked to the G.O.E.S. satellite and down-linked to the National Weather Service. The Minnesota Pollution Control Agency assists in data transfer as another cooperator.

Soil temperature information from the Six-Inch Temperature Network is provided on a map that also provides soil temperature information from the North Dakota NDAWN agricultural weather network sites located in Minnesota, University of Minnesota research centers, and other soil temperature sites. Most of these other sites do not report soil temperature at a six-inch depth, but still provide useful information that can estimate when soil temperatures are cool enough for fall application of nitrogen fertilizer to begin.

There are soil temperature sites on the map in southeast Minnesota which is an area where BMPs do not recommend fall application of nitrogen fertilizer due to the high leaching potential. The soil temperature sites are included to assist in the timing of fall manure applications, which like nitrogen fertilizer, are best done after soil cools to under 50 degrees F.


Cooperators


Other Soil Temperatures

Soil temperatures in Minnesota

 

Soil temperatures in adjacent states