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MDA adds to real-time soil temperature monitoring sites to aid farmers in fall fertilizer application


ST. PAUL, Minn. – The Minnesota Department of Agriculture (MDA) advises farmers and fertilizer applicators to check soil temperature and delay fall application of ammonium-based nitrogen fertilizers until soil temperature stays below 50˚F.

To assist tracking soil temperature, the MDA has added 22 new monitoring stations for a total of 48 stations on its on line soil temperature map at:

Soil temperature is measured at a six inch depth; the same depth anhydrous ammonia is typically applied. Station data on the MDA on-line map is updated every 15 minutes with the help of satellite uplink technology from the Minnesota Department of Natural Resources and the National Weather Service.

“In areas where fall nitrogen applications are appropriate, soil temperature, not harvest progress, should be your guide of when to apply,” says Bruce Montgomery, manager of the MDA Fertilizer Management Section. “Waiting until soil temperature stays below 50˚ F before applying anhydrous ammonia and urea increases the availability of nitrogen to next season’s crop and decreases the amount of nitrate that could potentially leach into groundwater.”

At temperatures below 50˚ F, microbe activity in the soil slows down, slowing the conversion to nitrate and the likelihood of nitrate movement with water.

According to Dr. Mark Seeley, University of Minnesota Extension climatologist, on average soil temperatures reach 50˚ F during the first week in October in northern Minnesota and the fourth week of October in southern Minnesota. These dates can vary widely year to year, making information provided by the real-time soil temperature monitoring stations valuable.

In addition to delaying application until soil temperature stays below 50˚ F, best management practices for nitrogen use developed by the University of Minnesota Extension recommend using a nitrification inhibitor when fall applying anhydrous ammonia in south-central Minnesota. Fall applied urea is not recommended for south-central Minnesota. In southeast Minnesota’s karst region and statewide on coarse-textured soils, fall application of nitrogen fertilizer is not recommended regardless of soil temperature. Specific nitrogen fertilizer use recommendations by region of the state can be found at:

The MDA has announced plans to develop a rule by 2018 which will restrict fall nitrogen fertilizer application in areas vulnerable to groundwater contamination. This would include southeast Minnesota’s karst region and statewide on coarse-textured soils. The rulemaking is part of the state’s revised Nitrogen Fertilizer Management Plan which was completed in 2015. More information on the plan can be found at


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