Illinois Fertilizer & Chemical Association
Supply · Service · Stewardship

Fall Nitrogen Guidelines

When stepping outside today, the first reaction is "brrr!"   As temperatures have plummeted from 80 degrees last week to highs of 50 degrees this week in much of Illinois, the next thing to think about is the 4Rs of fall fertilizer application--specifically fall ammonia applications.  
Each morning, IFCA will post a map of the State Water Survey's WARM site, which has indicators of the maximum daily soil temperature in bare soil at the 4-inch depth.  With regard to applying anhydrous ammonia in the fall, we continue to urge patience until soil temperatures fall to 50 degrees and the soil temps are not likely to rebound from those levels in any kind of significant way.  Normally the calendar date for this to occur, on average, is around November 1.  Last year it was after November 1 before soil temps fell to 50 degrees and this year it is looking to occur much earlier.  
We know that our members are keenly aware of the stewardship objectives of the fertilizer industry, so we know over the next week everyone will be looking at what everyone else is doing.  IFCA's advice is to use your best professional judgement--we all know what feels right and what doesn't.  Take soil temps yourself in the field of application, with the calendar also being a consideration.  Our industry has done a TERRIFIC job over the years effectively managing fall N and we know this year will be no different.  And when it all starts, BE SAFE.  As we have always stressed, please use the soil temperatures as your guide (daily maximum 4 inch temp at 50 degrees) and use a labeled nitrification inhibitor, at the manufacturer's recommended rate, in all fall applied ammonia.  We also recommend total N rates follow the MRTN; the Nitrogen Calculator for Illinois is again being updated and soon we will have an Apple app to also link to quickly to the N Rate Calculator - stay tuned!  
Go to and you will see the soil temperature map displayed on our homepage each morning.  If you click on the map it will expand for easy reading.  If you go to the WARM website to get the same map, you will have to create an account and login each time to access the maps.   
For more guidelines on fall nitrogen applications, Chapter 9 of the Illinois Agronomy Handbook provides an excellent explanation of the factors to consider.  For a refresher, click here to access the section on timing of fall nitrogen applications.