Check for residual nitrogen in fields this fall

Farmers should consider using a fall soil test to document the amount of nitrogen not used by this year’s crops and remaining in their fields.

Kay Shipman

Published: Sep 24, 2012

“If a crop didn’t take it (nitrogen) out, it’s out there; we’re finding it,” said Dan Schaefer, nutrient stewardship director of the Illinois Council for Best Management Practices (CBMP).

Between pulling soil samples last week, Schaefer paused to discuss the importance of fall soil nutrient tests. He calculated 60 pounds of nitrogen per acre remained in a Central Illinois field he had just sampled.

Schaefer estimated nitrogen levels range between 40 and 60 pounds per acre in “normal” fields this fall. “In some cases, it could be higher,” he warned.

Results from a fall soil test, especially in cornfields that will be planted to corn next year, should be used as a nitrogen inventory -- not for a fertilizer recommendation for the 2013 growing season, Schaefer said.

Schaefer suggested farmers who apply fall nitrogen apply 50 percent of their “nitrogen needs.” That is even more important this year given the amount of residual nitrogen left because of the drought.

Fabian Fernandez, University of Illinois soil fertility specialist, also encouraged farmers apply less nitrogen this fall.

“If you already have high nitrogen levels, let’s wait. You could lose the nitrogen in the soil and what you apply,” Fernandez warned.

Both Fernandez and Schaefer recommended farmers test soil for residual nitrogen levels next spring and adjust nitrogen rates accordingly.

Late October soil tests are key for obtaining accurate potassium recommendations because the soil has been so dry this year, added Fernandez. “For potassium, be aware the (test) results may be high if the soil is sampled in early fall,” he noted.

Timing is not as critical for soil testing for phosphorous or pH levels, he said.

Meanwhile, The U of I Extension and CBMP developed the Maximum Return to Nitrogen calculator for iPhone and Android smartphones.

Online Calculator

Download iPhone App

Download Android App

For limestone quality information, go to:
http://www.agr.state.il.us/news/pub/Limestonebooklet.html

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