Stalk Nitrate-N Test - A Diagnostic Tool for Evaluating Nitrogen Management Practices in Corn
By Manjula Nathan

With the increase in N fertilizer prices and growing concern for environment growers are becoming more interested in fine tuning fertilizer N applications for corn production. There are many diagnostic tools that are available for improving N management in corn. Researchers at Iowa Sate University have come up with the stalk nitrate N test as an effective diagnostic tool in improving N management in corn. This test gives you information on how well you have managed your nitrogen and doesn’t provide information on how much fertilizer N to apply for the coming season.

The stalk Nitrate N test is done in the lab where a 6" stalk (cut at 6 -8 inches above the soil surface at black layer stage, no leaves included) sample is dried, ground, and processed and analyzed for NO3- N. The numbers are compared to standards set by Iowa State University researchers based on field research. It is important to note for accurate results samples should be collected at black layer stage and not after harvest.

After collecting a representative sample six-inch stalk samples cut 6 - 8 inches above the soil surface, make sure to split the sample into two vertically and let it dry before mailing it to the lab. This would quicken the process of drying. It is preferable to sample a least a minimum of 10 stalks from the area of interest to have good representation and reliable results.

A stalk NO₃-N test value of less than 250 ppm is interpreted as low, nitrogen was probably deficient during the growing season. Test values of 250-700 ppm is marginal, it is possible that nitrogen shortage limited yield in this range, and 700-2000 is optimum, yield was not limited by a shortage of nitrogen in this range. Values in excess of 2000 ppm means excessive, nitrogen rate was too high or some production factor caused a yield reduction. Factors other than excessive use of N can such as drought and hail damage can lead to excess N in the stalk.

University of Missouri Soil and Plant Testing lab located at 23 Mumford Hall, UMC, Columbia, MO 65211 offers stalk NO₃-N test in corn for $12 per sample. You can reach the lab at 573-882-0623 or get information from the lab’s Website at http://soilplantlab.missouri.edu/soil on submitting samples. If you have any other questions about the test you can contact Manjula Nathan at 573-882-3250.

Manjula Nathan
573-882-3250