Ellen Phillips, Extension Educator-Crop Systems, 708-352-0109, firstname.lastname@example.org
Check soil temperatures to know when ammonium containing nitrogen fertilizer may be applied without excessive nitrification. The websites below give the current and long-term average of soil temperatures across Illinois.
The Illinois Agronomy Handbook states that at 50°F and below, the rate of nitrification is reduced since cool temperatures slows biological activity that converts nitrogen in the ammonium form to nitrate form. At soil temperatures below 60°F, anhydrous ammonia application with a nitrification inhibitor can begin. Inhibitors slow the conversion of ammonium to nitrate. They work best in moderately or well-drained soils or when there is excessive rainfall and frequent flooding.
Soil temperatures do fluctuate during the fall. It is not uncommon to have a period with soil temperatures below the accepted threshold for N application followed by a time where soil temperatures are above the accepted threshold. Therefore, when making your decision of when to apply nitrogen, use the current soil temperature and short- to long-term weather forecasts.
Current Soil Temperatures for Illinois
Long-term Soil Temperature Averages