To assist tracking soil temperature, the Minnesota Department of Agriculture has added 22 new monitoring stations for a total of 48 stations on its on‑line soil temperature map at: https://app.gisdata.mn.gov/mda-soiltemp/. The online map is updated every 15 minutes.

soil-temperature-monitoring-network

Real-time soil temperature readings in St. Peter, MN help 7 Mile Creek farmers determine when conditions are correct for fall applications of anhydrous ammonia (AA), a Nitrogen fertilizer.

“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.  Specific nitrogen fertilizer use recommendations by region of the state can be found at: www.mda.state.mn.us/nitrogenbmps.

The 7 Mile Creek Watershed Partnership offers farmers financial assistance (up to $30/acre) to adopt new nitrogen BMPs, and will be launching a nitrogen soil testing program in the coming months. Contact Karen for more information at (507) 301-9625 or kgalles@greatrivergreening.org