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Information from the Illinois Agronomy
Handbook, available from the University of Illinois College of ACES,
states that fall soil temperatures determine when
ammonium-containing N fertilizer may be applied without excessive
nitrification. The nitrification rate is reduced at temperatures of
50 degrees F and below. Anhydrous ammonia application with a
nitrification inhibitor may begin at soil temperatures below 60
degrees. The 4-inch bare soil temperature at 10 a.m. each day is
used to make this determination.
With a grant from the Illinois
Department of Agriculture Fertilizer Research and Education Program,
the Illinois State Water Survey's Water and Atmospheric Resources
Monitoring Program
developed daily maps of soil temperatures at 19 sites across
Illinois 4 inches below a bare soil surface observed between 9 and
10 a.m. on the previous day. Daily midnight-to-midnight maximum and
minimum temperatures at the same depth also are provided for each
location.
According to Scott, "Soil
temperature fluctuations during the fall may result in days with
temperatures below the accepted threshold for N application,
followed by an extended period of time when soil temperatures once
again exceed the accepted threshold. Thus, users need to be aware of
both current soil temperatures and short- to long-term weather
forecasts."
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The
Water and Atmospheric Resources
Monitoring website provides mean dates when soil temperatures drop
and remain below 60 degrees and 50 degrees, respectively, as well as
daily values of soil temperatures under a sod surface at depths of
both 4 and 8 inches. In addition, daily observations on air
temperature, dew point, wind speed and direction, solar radiation,
potential evapotranspiration, precipitation, and growing and pest
degree-day information across Illinois are presented for the most
recent seven days.
Map data, updated by 4 a.m. each
day, represent conditions at actual locations where observations are
taken. Elsewhere, the information should be viewed as a guide to
general soil temperatures within a given region and to current
temperature trends progressing across the state.
"Farmers and applicators are
encouraged to monitor the soil temperature of each field to be
treated, before fall application of N fertilizer," Scott said. "The
Illinois Agronomy Handbook recommends no fall N application south of
Illinois Route 16, roughly the southern third of Illinois."
[News release provided by
Eva Kingston, editor,
Illinois State Water Survey]
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