About Daily Soil 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 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 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.
The Illinois Agronomy Handbook states that soil temperatures in autumn determine when ammonium, containing nitrogen fertilizer may be applied without excessive nitrification. It is recommended that that autumn applications should be performed when the daily maximum bare soil temperature at 4 inches is below 50° F. 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.
It is also recommended that no autumn N application should occur south of the terminal moraine of the last glacier which roughly corresponds to Illinois Route 16.