Reviewing the Nitrogen Program After Harvest
October 1, 2024
As harvest season wraps up, there is a lot to review from the previous growing season. Topics coming to mind include:
- How did that product perform?
- Did that fungicide pass pay for itself?
- How did my nitrogen (N) program work?
The last question is the topic for this article. There are various ways to review N availability during the season such as soil sampling for available nitrate, leaf tissue sampling and/or stalk nitrate test.1,2 However, once the crop has been harvested, the only test left to evaluate N availability is a fall nitrate test.
Interpreting the Test
The goal of using a fall nitrate test is to determine that amount of plant available N left in the soil (Table 1).3 An excess amount of nitrate could indicate more N was applied during the season than what the crop required. If current yields were in line with the yield history for a field, then N applications were likely adequate for the growing season. If the N test comes back low, full yield potential may not have been achieved. The nitrate test can’t answer that question now but indicators during and after the season would be plant health as well as test weight. If the test has low nitrate and the crop deteriorated quickly with shrunken kernels at the base of the cob, it is likely the crop didn’t have adequate N during the growing season. In this situation, more N, a different source of N, or timing of application should be considered.
Table 1. Nitrate Concentration from Fall Nitrate Test.
Poor growing conditions such as drought, high heat, or premature plant death due to disease can interfere with N uptake. In these situations, the fall nitrate test could indicate an excess of N when in essence a healthy crop may have utilized the available N.
Conclusion
Finally, market conditions always play a factor in the upcoming season and when they look bearish, the topic of cost savings always comes to the forefront of producers’ minds. Nitrogen is one of the top contributors to yield every season so special consideration should be made when thinking of cutting costs from the N bucket. A fall nitrate test is a simple way to try and determine if that is a feasible measure to consider for the next growing season.
For additional information on how to conduct a nitrate test, please read Performing a Corn Stalk Nitrate Test.
Channel Agronomist
Ryan Becker
Sources
1Soil nitrate test for corn. Michigan State University. https://www.canr.msu.edu/spnl/soil-nitrate-test-for-corn.
2Diaz, D.R. 2021. Plant analysis for testing nutrient levels in corn. Agronomy eUpdates. Department of Agronomy. Kansas State University. https://eupdate.agronomy.ksu.edu/article/plant-analysis-for-testing-nutrient-levels-in-corn-448-3#:~:text=Plants%20more%20than%2012%20inches,the%20field%20at%20silk%20emergence.
3Kaiser, D. and Fernandez, F. 2024 (2020). How to take and interpret the basal stalk nitrate test. Minnesota Crop News. University of Minnesota. https://blog-crop-news.extension.umn.edu/2020/09/how-to-take-and-interpret-basal-stalk.html
Web sources verified 8/19/24. 1110_442993