Nitrogen (N) is very important for corn, as it’s needed for growth and reproduction. Nitrogen is a very dynamic component in the soil, changing between various forms, but plants can’t absorb or use all forms of N. Instead, they absorb inorganic N, primarily nitrate and ammonium.

Renuka Mathur, Ph.D., the UNH Extension state specialist in soil health, is very educated on the factors that influence N levels. The moisture level and temperature of the environment need to be ideal for organic N in the soil to transform into nitrate and ammonium for plants to use. If the plants are unable to use the N available in your soil, it doesn’t matter how much you apply.

Mathur thinks it’s very important to test how well your plants are taking up N from their surrounding soil. The corn stalk nitrate test (CSNT) is “very, very, very reliable,” she said, as it’s accurate at assessing if your current N application is adequate enough for your plants. The CSNT is conducted at the end of the growing season after the plants have matured.

In order for the CSNT to be accurate, samples need to be collected at the right time, in the right way and in the right conditions. Samples should be collected after the stalk has a one-quarter milk line and less than three weeks after black layer formation. The stalk samples should be harvested starting at six inches from the ground and up to 14 inches from the ground. This range leads to the most accurate results. Samples should not be taken from diseased stalks or during a drought.

The harvested stalk should be cut lengthwise into four quarters and placed in a breathable container (like a paper bag) to prevent molding. Cutting the stalk into quarters helps speed up the drying process required for testing, but they must be cut lengthwise since N travels from the base of the plant to the top. If the samples are not being sent to the lab immediately, they should be placed in the fridge to help preserve them, but never placed in the freezer.

The results will show how successful your N management was throughout the entire season and help you adjust your plan for the following growing seasons. Ideal results are between 700 and 2,000 ppm in the corn stalk. Falling in this optimal range suggests “you have provided an adequate supply of N to the plant,” Mathur explained.

If the results show less than 700 ppm in the stalk, you may be able to increase N levels to potentially increase your yield. Anything over 2,000 ppm is considered excessive, and less N could be provided in the future.

It’s important to note the CSNT is not a predictive test, but instead should be used to monitor yearly trends. Since N levels are influenced by many uncontrollable environmental factors, you may have a low ppm result one year but an optimal result the next with no changes to your management.

No matter the result, take the time to address any problems, determine all potential factors and monitor the levels for a few years to find a trend.