Optimize corn yields with late season nitrate testing

By Blake Jackson

Nitrogen (N) is a crucial nutrient for corn production, but its management can be challenging due to its various forms, transformations, and potential losses.

While several tools exist to improve N fertilizer recommendations, uncertainty remains in determining optimal application rates.

This often leads to over-application of N, which can negatively impact both economic and environmental performance.

The late-season cornstalk nitrate test (CSNT) is a valuable diagnostic tool that can help assess whether excess N was applied to a corn crop.

By measuring nitrate concentrations in cornstalks at the end of the growing season, producers can identify fields that were low, optimal, or excessive in N availability.

Historically, CSNT results were interpreted as low (less than 700 ppm nitrate-N), optimal (700-2,000 ppm nitrate-N), or excessive (greater than 2,000 ppm nitrate-N).

While the CSNT is accurate at identifying excessive N application, there is less certainty regarding the optimal range.

Research has shown that corn yields may not decline due to N deficiency until stalk nitrate concentrations fall below 250 ppm nitrate-N. However, the optimal range has been set at 700-2,000 ppm nitrate-N to ensure sufficient N supply.

Recent studies have analyzed CSNT results in various N rate trials to refine the interpretive categories. Preliminary findings suggest that the most profitable yield response to N fertilizer addition corresponded to CSNT levels between 115 and 315 ppm nitrate-N.

This indicates that maintaining sufficient N supply is crucial for preventing yield losses, while reducing excess N applications can improve profits.

To effectively use the CSNT, producers should conduct the test at the one-quarter milk line and collect representative plant samples from the field. The samples can be analyzed by a laboratory to determine nitrate concentrations.

By understanding the CSNT results and considering other factors such as weather patterns and previous management practices, producers can make informed decisions about N fertilizer applications in future growing seasons. This can help optimize N use, improve crop yields, and reduce environmental impacts.

Photo Credit: gettyimages-awakr10