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Maps help with timing of post-harvest nitrogen fertilizer applications   Send a link to a friend

[OCT. 15, 2004]  CHAMPAIGN -- "Farmers and agribusiness operators have access to maps showing soil temperatures across Illinois ( to help them decide when to apply fall nitrogen (N) fertilizer," said Illinois State Water Survey meteorologist Bob Scott.

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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