The MDA soil temperature network provides 6 inch soil temperatures at various locations across southern Minnesota. Best management practices for fall fertilizer application in Minnesota refer to a 6 inch soil temperature level. Most other reporting services report 2, 4, and 8 inch soil temps.
See a map of the soil temperature network sites, including links to the last week's temperature.
Best management practices (BMPs) for nitrogen use for corn production in Minnesota recommends that urea (46-0-0) and anhydrous ammonia (82-0-0) applied in the fall should be delayed until soil temperatures at 6 inches stabilizes 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. Ammonium binds tightly to soil colloid surfaces and clay inter-layers. If average soil temperatures are above 50 deg F. soil microbes can transform ammonium into nitrite, and then into nitrate. The nitrate form is highly mobile and can leach from soil resulting less available nitrogen for crops in the following growing season. The leached nitrate can concentrate in ground water and cause elevated nitrate levels. Nitrate levels exceeding 10 mg/l, are above the safe drinking water standard established by the EPA.
BMPs are practices that are capable of preventing and minimizing degradation of ground water and surface water, considering economic factors, availability, technical feasibility, effectiveness, and environmental effects.
The Minnesota Department of Agriculture is responsible for the development, promotion and evaluation of Best Management Practices (BMPs) for pesticide and nitrogen fertilizer use, and provides information on best management practices related to water and soil quality protection
The 6 inch Soil Temp Network is a cooperative effort between the Minnesota Department of Natural Resources (MN DNR) and the MDA. All of the current 6 inch soil temperature sites are co-located at MN 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-link to the National Weather Service.
Pesticide & Fertilizer Management Division
Minnesota Department of Agriculture (MDA), 625 Robert Street N, St. Paul, MN 55155-2538, firstname.lastname@example.org