Corn Stalk Nitrate Testing

To evaluate nitrogen, take a closer look at corn stalks…

End of season corn stalk testing helps give insight into how well nitrogen fertilizer was utilized by the corn plant. These results won’t change your yield, but it provides more data to use for future management decisions.
“There isn’t a visible sign for over fertilizing a corn field,” notes Steve Peterson, VP, Laboratory Services. “Corn stalk testing can alert you to excess nitrogen levels and help plan for next year.”
Corn stalk N concentrations can be divided into categories for interpretation, ranging from Low/Deficient to High/Excess. Here’s how it works:
– Corn plants with inadequate available nitrogen remove nitrogen from lower stalks and leaves during the grain filling period.
– Corn plants with excess nitrogen accumulate nitrate in their lower stalks at the end of the season.
A relationship between stalk nitrate concentrations and relative yields is derived from trials. Studies at Purdue and Iowa State University show that the nitrogen status of a corn crop can be assessed by measuring nitrate concentrations in the lower portion of cornstalks at the end of the growing season.

How to Sample Corn Stalks

  • When to Sample: 1 – 3 weeks after black layer has formed on 80% of the kernels of most ears.
  • What to Sample: Cut stalk segments 8 inches long. Take stalk segments from between 6 and 14 inches above the soil. Avoid damaged stalks. Remove sheaths.
  • Amount of Sample: Randomly collect 15 stalk segments within an area not larger than 10 acres. Together, these stalks form one ‘composite’ sample. Areas of differing soil types or management should be sampled separately.
  • Shipping: Place stalks in a paper bag. Do not use plastic bags! Ship samples as soon as possible. Refrigerate if delay in shipping is one or more days. Do not freeze.