For an experienced producer, it can be fairly easy to know when a corn field is nitrogen deficient. The yellowing of the lower leaves is a tell-tale sign that a corn plant is lacking nitrogen. In contrast, it is difficult to know if a corn crop is over fertilized or if fertilizer has been applied in excess of what the crop really needs. Many farmers and ag professionals are searching for a diagnostic tool that can improve nitrogen fertilizer management. The basal stalk nitrate test is one of these tools.

It is important to note this is a diagnostic, not a predictive, test. Results do not provide an absolute determination of under or over application. Rather, results from this test provide general management guidelines and help inform discussions about on-farm nutrient management.

In general, the basal stalk nitrate test estimates how much nitrogen is left over at the end of the growing season.

How it works

  • At the end of the season stalk samples are collected. Four sampling locations are identified in each field. After the corn crop has reached full maturity, ten basal stalk samples are collected from each of the four sampling locations in the field.
  • Sampling protocol is informed by aerial photography and vegetation index images. These images are used to help guide where to collect representative field samples. Soil samples are also used to inform the sampling protocol.
  • Stalks are cut six inches above the ground. An eight inch stalk sample is collected.
  • Stalks are submitted for nitrate-nitrogen analysis.
  • Researchers have found that concentrations above 2000 parts per million (ppm) indicate a high probability that nitrogen was in excess of what the corn crop needed. If concentrations are below 700 ppm there is a high probability that nitrogen was deficient.
  • Since samples are collected at the end of the growing season, interpretation of results offers no assistance in fine-tuning nitrogen management for the current year. Results provide insight into nitrogen management for future years.
  • Results help producers identify areas of the field where nitrogen uptake is excessive (no yield benefit) and thus costly to the grower and possibly the environment.

Producers are able to use this information to make nitrogen management changes that are appropriate for their farm. When possible, nitrogen management trials will be supported to evaluate changes (i.e. compare nitrogen rates) producers want to see in their field.

To learn more, read the University of Minnesota Extension's publication (PDF) regarding end of season basal stalk nitrate testing.