Stalk Nitrate-N Test – A Tool For Evaluating Nitrogen Management Practices In Corn

Dr. Manjula Nathan

COLUMBIA, MO.
    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 a diagnostic tool in improving N management in corn (www.ncagr.gov/agronomi/pdffiles/cornstalk.pdf?). 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 (samples should be cut at 6 -8” above the soil surface, at black layer stage, no leaves included) sample is dried, ground, and processed and analyzed for nitrate-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 one to three weeks after 80 percent of the kernels reach black layer stage (physiological maturity) and not after harvest.
    After collecting a representative sample 6” stalk samples cut 6 – 8” 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.
    In general, larger amount of plant available N in the soil during the time period before plant maturity results in higher concentration of nitrates in the lower portion of the stalk. However, stalk nitrate-N can be greatly influenced by other factors like soil moisture and precipitation.
    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 $10 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. When submitting samples corn stalk Nitrate-N test, use the plant analysis form http://soilplantlab.missouri.edu/soil/forms/index.aspx and select Nitrate-N test. There is sample grinding fee for processing the samples. If you have any other questions about the test you can contact Manjula Nathan at 573-882-3250.
    Ref:
    Blackmer, A.M. and A. Mallarino, 1996. Cornstalk testing to evaluate nitrogen management. University Extension, Iowa State University. Guide: PM 1584. http://www.ncagr.gov/agronomi/pdffiles/cornstalk.pdf
    Bob Nielson, 2003. End of season Corn Stalk Nitrate Test. Department of Agronomy. Purdue University. Sept 2003. http://www.agry.purdue.edu/ext/corn/news/articles.03/stalknitratetest-0915.html
    John Sawyer, 2010. Stalk nitrate tests- Crop News, Sept 14, 2010. Iowa State University Extension and Outreach. http://www.extension.iastate.edu/CropNews/2010/0914sawyer.htm.∆
DR. MANJULA NATHAN: Extension Associate Professor Division of Plant Sciences, University of Missouri