Purdue expert offers research update on cornstalk nitrate tests

October 3, 2013  

WEST LAFAYETTE, Ind. - End-of-season cornstalk nitrate tests conducted over a series of years can help corn growers better manage nitrogen by showing whether soil nitrogen applied during the season met or exceeded crop needs, a Purdue Extension agronomist says.

Farmers can use the results to choose the best nitrogen source, application timing, placement and rates.

The test works because as corn approaches physiological maturity, plants that don't have access to enough nitrogen will take nitrate from the lower stalk and move it to the ear. Conversely, if a plant has too much nitrogen, nitrate accumulates in the lower portion of the stalk.

In order for cornstalk nitrate test (CSNT) results to help farmers alter their nitrogen management programs, the test needs to be conducted in multiple years, Jim Camberato said in a recent research update in Purdue Extension's Pest and Crop Newsletter.

"Multiple seasons of CSNT evaluation are warranted before altering an N management program because the optimum rate varies from season to season," he said.

The reason for the variation is that a series of factors affect the optimum rate. They include differences in soil nitrogen supply, loss of nitrogen from the root zone and differences in corn hybrid nitrogen use. Pests and weeds also can affect the amount of nitrogen used.

"The average correct N rate for maximizing profit over the long term is almost certainly wrong in any one season - either too much or too little," Camberato said. "Thus, the evaluation of an N management system with the CSNT or any other N-assessment tool on any given field in a single season is interesting, but not particularly useful in making management decisions for future years."

Instead, he recommended that growers maintain a database of end-of-season cornstalk nitrate tests and that they consider all of the data before adjusting fertilizer-based nitrogen-management programs.

The best way to conduct a cornstalk nitrate test is to take 15 or more 8-inch stalk segments beginning 6 inches above the soil surface from representative areas of a field. The samples need to be collected within a few weeks after black layer, the point when corn is considered physiologically mature. They can then be sent to a lab and analyzed for nitrate-nitrogen (NO3-N), and the results can be compared with recommended rates in Indiana.

Nitrate concentrations between 450 parts per million and 2,000 parts per million are considered optimal, while anything higher than 2,000 ppm is considered excessive, Camberato said.

More in-depth information about cornstalk nitrate testing is available in Purdue Extension's free bulletin Cornstalk Testing to Evaluate the Nitrogen Status of Mature Corn: Nitrogen Management Assurance. The bulletin can be downloaded through Purdue Extension's The Education Store by searching for AY-322-W. 

Writer: Jennifer Stewart, 765-494-6682, jsstewar@purdue.edu  

Source: Jim Camberato, 765-496-9338, jcambera@purdue.edu 

Ag Communications: (765) 494-2722;
Keith Robinson, robins89@purdue.edu
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