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Stalk Nitrate Test Evaluates Fertility Programs

Excess moisture this growing season may have you second-guessing your nitrogen (N) fertilizer program. Gain insight into how well corn plants were able to utilize N with an end-of-season stalk nitrate test.

“Corn expresses symptoms when nitrogen is deficient,” says Steve Peterson, AgSource Laboratories vice president, laboratory services. “But there isn’t a visible sign for overfertilizing. Cornstalk testing can alert you to excess N levels and help you plan for next year.”

Corn plants with inadequate available N remove N from lower cornstalks and leaves during the grain filling period. Plants with excess N accumulate nitrate in their lower stalks at the end of the season.

To see how well your fertilizer program did, consider trying the stalk nitrate test. It’s too late to make adjustments for this year, but the results can provide feedback for future fertility needs.

Results range from low/deficient to high/excess. 

Sampling Guidelines

  1. Take samples one to three weeks after black layers have formed on 80% of the kernels of most ears.
  2. Samples should be taken between 6 and 14 inches above the soil. Stalk samples should be 8 inches long. Don’t pull samples from damaged stalks.
  3. AgSource Laboratories prefers 15 samples to be randomly collected from within an area not larger than 10 acres. Together, these stalks form one 'composite' sample. Sample different soil types or management zones separately.
  4. Place stalks in a paper bag and ship them to the lab as soon as possible for analysis. Samples should be refrigerated if shipping is delayed by a day or more. Samples shouldn’t be placed in the freezer.
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