Corn Nitrogen Update

By Daniel Hudson, UVM Extension Agronomist

It is no secret that many of the corn fields are nitrogen deficient right now – mostly due to leaching. The result is that many farmers will be applying more sidedress nitrogen than usual, and many who typically rely entirely on manure will need to sidedress in order to attain the full yield potential of their corn crop.

Here are some thoughts to consider as you are thinking about sidedressing nitrogen on your corn next week.

  • Most of the pre-sidedress nitrate test (PSNT) results are coming back very low, indicating that a considerable amount of nitrogen fertilizer is needed in order to optimize crop yield. While I am sure some fields need no sidedress N, all of the recommendations that I have seen have ranged from 50 to 130 pounds of sidedress N per acre. That does not mean that you have a similar problem in your field. You cannot know if you have a problem or how severe the problem is unless you check. Using the PSNT is a good place to start. If you think it is too late for the PSNT, please contact me and we can consider some other strategies to come up with a recommendation.
  • While it is convenient to have urea and ammonium nitrate (UAN) applied by a custom operator, it is one of the more expensive forms of sidedress N. Keep in mind that the nitrate is subject to leaching immediately and the urea fraction is subject to volatilization losses. This time of year, including a urease inhibitor with UAN is a good idea. Using streamer bars or drop nozzles is advisable.
  •  If you are sidedressing your corn with urea, it is a very good idea to use a urase inhibitor unless you KNOW that it is going to rain a lot (at least 0.5 inches) within a day or two. With damp soils, sunny weather, and high temperatures, it would be very easy to have volatilization losses exceeding 25% in a matter of days. In these conditions, using a urease inhibitor such as Agrotain® is likely to be a profitable decision. [This is not an endorsement of the Agrotain® brand by myself or UVM.]
  • For those who applied urea before planting or before emergence, do not assume that the N from that product is still in the soil. In one case that I am aware of, urea was applied at 200 lb/ac near planting time. When the soil nitrate and ammonium levels were recently checked, the report indicated that most (if not all) of than nitrogen was lost.
  • When using urea for sidedressing your corn, it is a good idea to wait until the leaves are dry. Wet leaves will cause more of the urea granules to stick to the plant tissue and cause burning. If you expect a lot of rain in the next few days, that is even better.

About Daniel Hudson

Daniel is an agronomist for University of Vermont Extension in the areas of agriculture and nutrient management.
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