About Daily Soil Temperature Maps
The Illinois State Water Survey,
through a grant from the Illinois
Department of Agriculture Fertilizer Research and Education program,
has initiated daily dissemination of maps showing 4-inch bare soil temperatures
across the state based on observations taken at selected Illinois Climate
Network sites. These data are intended to assist Illinois farmers with
timing of post-harvest nitrogen (N) fertilizer application. The information
displayed is specifically representative of the actual locations where
soil temperature observations are made. Elsewhere, these data should be
viewed as a guide to general soil temperatures within a given region,
and as indicative of current temperature trends progressing across the
state. Farmers and applicators should monitor the soil temperature of
each field before fall application of N fertilizer.
Individual daily maps are analyses of the observed soil temperatures
across Illinois on the previous day at a depth of 4 inches below a bare
soil surface. Figures show:
- soil temperature between 9:00 a.m. - 10:00 a.m. (Central Standard
Time) on the previous day
- daily (midnight to midnight) maximum soil temperature on the previous
day
- daily (midnight to midnight) minimum soil temperature on the previous
day
Charts will be updated by 4 am each day.
Users should be aware that soil temperature fluctuations during the 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. Therefore, users are advised to be aware
of both the current soil temperature and short- to long-term weather forecasts.
The Illinois
Agronomy Handbook states that soil temperatures in autumn determine
when ammonium, containing nitrogen fertilizer may be applied without excessive
nitrification. At 50°F and below, the rate of nitrification is reduced.
At soil temperatures below 60°F, anhydrous ammonia application with
a nitrification inhibitor can begin. The Illinois
Agronomy Handbook recommends that no fall N application should
occur south of Illinois Route 16, roughly the southern third of Illinois.
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