Corn Stalk Nitrate Testing

The Corn Stalk Nitrate Test (CSNT) was developed by Iowa State University agronomists to determine if growers were using the proper amounts of nitrogen for corn production.  This is assessed by measuring the amount of nitrate - nitrogen present in the lower portion of the corn stalk around the time the plant reaches physiological maturity.  Corn plants suffering from inadequate N availability remove N from the lower cornstalks and leaves during the grain-filling period.  Corn plants that have more N than needed to attain maximum yields, however, accumulate nitrate in their lower stalks at the end of the season.  Several factors, including weather, can have a profound effect on the results of the test.

SAMPLE GUIDELINES

Samples should be collected between 1/4 milkline to 3 weeks after black layer has formed on 80% of the kernels of most ears.  Field test areas should not be larger than 10 acres.  Collect 15 stalks and remove an 8” segment between 6” and 14” above the soil.  Place in paper bag (not plastic). Refrigerate if delay in shipping is one or more days.  Do not freeze.

INTERPRETATIONS - CSNT

Low

Less than 250 ppm

Indicates high probability that greater availability of N would have resulted in higher yields.  Visual signs of N deficiency are usually observed in this range.

Marginal

250 - 700 ppm nitrate-N (ISU)

Producers should not be concerned when samples test in this range. N availability was close to the minimum amount needed for maximum yields but should not be the target for good nitrogen management.

Optimal

250-2000 ppm nitrate-N (Purdue), 700-2000 ppm nitrate-N (ISU)

Indicates that N supplies were sufficient for maximum yields.

Excess

Greater than 2000 ppm nitrate-N

Indicates that N supplies were above levels needed to maximize profits.

 

The CSNT does not directly indicate how much a N application should be increased or decreased.  However, the use of this test consistently from year to year can be a valuable tool when adjusting N rates.  Since the development of this test, nitrogen prices have increased substantially, increasing the need for sound nitrogen management.  In addition, nitrogen in ground and surface waters can be a major environmental concern.  From both an environmental and an economic perspective, any tool that can help a grower manage nitrogen usage should be seriously considered.  Additional information on the corn stalk nitrate test can be found in our factsheet, “Corn Stalk Nitrate Test”, available on our website.


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