Daily Soil Temperature Maps Provide Help, Illinois State Water Survey

Press Release

For Immediate Release October 16, 2001
Daily Soil Temperature Maps Provide Help
with Timing of Post-Harvest Nitrogen Applications

Source:   
Contact:   
Bob Scott, meteorologist - (217) 333-4966, Fax: (217) 244-0777, r-scott5@illinois.edu
Eva Kingston - (217) 244-7270, Fax: (217) 333-6540, eva@sws.uiuc.edu

Through a grant from the Illinois Department of Agriculture Fertilizer Research and Education program, farmers in Illinois now have access to a new Web tool that provides assistance with timing of post-harvest nitrogen fertilizer applications.

The Illinois State Water Survey (ISWS), a division of the Illinois Department of Natural Resources, is now providing three daily maps on the Web (http://www.sws.uiuc.edu/warm/soiltemp.asp) that show soil temperatures across Illinois. The maps, updated by 9 a.m. each day, are based on continuous observations of soil temperatures at selected Illinois Climate Network sites.

"These data are representative of the actual locations at which soil temperature observations are made. They should be viewed as a guide to general soil temperatures within a given region and as an indication of current temperature trends across the state. Due to the variability in temperatures that can exist in a local region, farmers and applicators should verify the soil temperature of each field before fall application of nitrogen fertilizer," says ISWS meteorologist Bob Scott.

The maps represent analyses of soil temperatures observed the previous day across Illinois at a depth of 4 inches below a bare soil surface. They show the average temperature between 9:00 a.m. and 10:00 a.m. (Central Standard Time) and the daily (midnight to midnight) maximum and minimum temperatures across the state for the previous day.

Map users are encouraged to be aware of both the current soil temperatures and short- to long-term weather forecasts. "Soil temperature fluctuations during fall may result in periods with soil temperatures below the accepted threshold for N application followed by an extended period with soil temperatures above the accepted threshold," says Scott.

The Illinois Agronomy Handbook, available from the University of Illinois College of ACES, states that fall soil temperatures determine when ammonium containing nitrogen fertilizer may be applied without the occurrence of excessive nitrification. The rate of nitrification is reduced at soil temperatures of 50°F and below. At soil temperatures below 60°F, application of anhydrous ammonia with a nitrification inhibitor can begin.

Separate maps on the same Web page show the average dates when soil temperatures drop and remain below 60°F and 50°F, respectively. Due to occasional periods of warm weather in winter, the handbook does not recommend fall application of nitrogen south of Illinois Route 16, roughly the southern third of the state.

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