Grading Your Nitrogen Plan With the Corn Stalk Nitrate Test

One of the biggest questions for a grower at the end of the growing season frequently revolves around their nitrogen (N) program. “Did I apply enough?” “Did I overapply, and waste money?” A lot of times, these questions go unanswered. Often, growers see their fields are dark green and may conclude that their N management plan was optimum. Unfortunately, it is virtually impossible to differentiate an optimum N rate from overapplication through visual differences. However, there is an end-of-season test called the corn stalk nitrate test (CSNT) that is available to evaluate N plans at the end of the year. The CSNT can be used to help determine if a field was overfertilized and can provide insights for future N program modifications. What it won’t do is indicate how much. The CSNT is also a great resource in fields that were manured with an uncertainty for N content.

Sampling for the test is straightforward and is best performed one to three weeks after the black layer growth stage. Fifteen 8-inch stalk segments from 6 to 14 inches above the ground should be collected from various areas for a representative sample. It is important that the leaf sheaths are removed and that stalks are free of disease, insect or hail damage for accuracy. Once collected, samples should be kept cool and dry and submitted for nitrate analysis as soon as possible.

Once results are obtained, they can be interpreted with the following table: 



Table 1. Interpretation of Corn Stalk Nitrate Test (CSNT) Results
Category Nitrate (NO3-N) Concentration (ppm)     


Less than 250


250 to 2,000


Greater than 2,000

When concentrations are consistently categorized as high, or greater than 2,000 NO3-N, there is a high probability that N fertilization was excessive and not economically optimized. When patterns from multiple samples and/or years are observed, then adjustments to the N rate can be considered. It’s important that multiple levels of data are used to minimize any bias or variability that may occur during the sampling process.

The CSNT can be a helpful tool to identify an excessive N application and potentially help reduce input costs. 

Aaron Sindelar



Sawyer, J.E., and Mallarino, A.P. 2018. Use of the end-of-season corn stalk nitrate test in Iowa corn production. CROP 3154. Iowa State University. 


Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields. 

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