Questions about the amount of residual nitrogen sparked an inventory of soil nitrate levels around the state. The University of Illinois and the Illinois Council for Best Management Practices recommend farmers base their fertility budgets on fall soil test results.
Anhydrous should not be applied until soil temperatures at the 4-inch depth have reached and will remain below 60 degrees Fahrenheit if a nitrification inhibitor is included.
If no inhibitor is included, don’t apply anhydrous until soil temperatures reach and will remain below 50 degrees.
“While applying once temperatures are 50 degrees Fahrenheit does not automatically prevent nitrogen loss, it does provide a better chance to protect your investment,” said Fabian Fernandez, U of I crop scientist.
No fall nitrogen should be applied on any field south of a line extending from about Jerseyville to West Union (Illinois Route 16).
The Illinois State Water Survey posts daily temperatures of soil at the 4-inch depth. Go to http://isws.illinois.edu/warm/soiltemp.asp
On average, soil temperatures reach 50 degrees Fahrenheit and continue to go down in the first week of November in Central and Northern Illinois.