Publication Shows Benefits of End-of-Season Nitrogen Testing

Test can help farmers evaluate nitrogen use in corn for the season that just ended

August 23, 2018, 11:49 am | John Sawyer, Antonio Mallarino

corn by Wakr10/, Iowa ― Using nitrogen fertilizer and manure for corn production is a typical practice that can produce optimal yield and increased profitability. As harvest draws near and farmers begin to turn their thoughts to the next planting season, measuring the amount of nitrogen in corn stalks after maturity (black layer) can help assess the current year and help with decisions about nitrogen management in future years.

Understanding this type of nitrogen test for corn is the focus of a newly revised publication, “Use of the End-of-Season Corn Stalk Nitrate Test in Iowa Corn Production” (CROP 3154) available through the ISU Extension Store. The publication is written by John Sawyer and Antonio Mallarino, professors and extension specialists in agronomy at Iowa State University.

“This publication provides updated research on the corn stalk nitrate test to help readers understand what the research is telling us and to update the interpretations we can draw from testing,” Sawyer said. Detailed graphs in the publication provide data on the relationship between the CSNT and relative corn yield response to nitrogen.

Conducting this type of plant testing can provide valuable guidance when determining application rates and management for future corn crops.

“This test works best by indicating when there was too much available nitrogen in the soil system during the current corn crop,” Sawyer said. “It’s important for farmers to understand if they have a system that is supplying more nitrogen than needed.”

There are three categories of interpretation discussed in the publication – high, sufficient and low. Research conducted at Iowa State and in other Midwestern states has consistently shown test concentrations greater than 2,000 ppm of nitrate-nitrogen to be in the high category, and that changes can be made to application rates. Test results in the 250-2,000 ppm range indicate a sufficient nitrogen supply, while results less than 250 ppm indicate a deficient supply.

The test should be conducted for several years before making major changes to application rates or management practices. In no case does the test indicate exactly how much to change an application rate.

“Our goal in this publication is to provide updated research information on the CSNT, which will hopefully enhance use of the test,” Sawyer said.

The publication also provides clear instructions for how to sample corn stalks for the CSNT, as well as recommendations for preserving the sample and sending it to a testing lab.


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