June 30 Corn Nitrogen Update!

Everyone suspects that there has been a fair amount of leaching of soil nitrate from corn fields in the Northeast this year, but how much?  Since most of the corn is more than 12 inches tall, it is too late to use the pre-sidedress nitrate test (PSNT) on most fields; recommendations are not valid if the samples are taken after that time.  It is not too late to use the Adapt-N program. Recommendations I have seen generated from Adapt-N have ranged from 60 to 150 lb/acre of sidedress nitrogen – – even when a lot of manure was applied and accounted for.  For example, the program shows that local field with soils that are not particularly coarse-textured lost over 56 pounds of N to leaching since June 1.  Some of you may think that is a lot, others may be surprised that more was not lost.  Either way, if the corn is missing 56 pounds of N that it needs, the yield will be affected.  Twenty tons of corn contains 180 pounds of actual nitrogen!

Plant demand for nitrogen is about to skyrocket.  While nitrogen fertilizer can have a positive impact when applied up to tasseling (if you can get in the field), the ideal time to apply sidedress nitrogen is at or before the 10-leaf stage (V10).  If you are putting liquid fertilizer (32% UAN) on corn, it is ideal to use drop hoses/tubes to dribble the fertilizer between the rows to avoid leaf damage.

I strongly believe that recommendations from Adapt-N are superior to those generated by the PSNT, especially in unusual years like this.  It is able to account for nitrogen uptake, loss, and need based on the manure you applied (analysis, date of application, incorporation), planting date, expected yield, hybrid relative maturity, fertilizer already applied, your local weather, and your soil types.  It can also generate a ‘virtual PSNT’; that is, it can predict what the pre-sidedress nitrate test (PSNT) would be if someone had physically taken a sample.  In my experience, this prediction is accurate.  If you really want to get into the details, you can compare the recommendation that the PSNT would have given you with the recommendation that Adapt-N gives you.  Also, if you give the program your email address, it will send you a regular ‘nitrogen status update’ that will help you to understand what is going on in the crop and soils of your fields.

One farm in central Vermont a 25 ton/ac expected corn silage yield recently had a ‘virtual PSNT’ of 7.6 ppm (generated by Adapt-N).  If this level of nitrate were found on an actual PSNT report, the sidedress N recommendation would be 125 lb/ac of actual N.  Because Adapt-N was informed about planting date (in June) and actual and historical weather data, it is giving a sidedress-N recommendation of 150 lb/ac for this field.  This is higher than the PSNT would recommend . . . but it is based on better information.

‘Whoa!  Wait!  I have NEVER applied 150 lb/ac of sidedress nitrogen to my corn.  I have never needed it, and never had a crop failure because I didn’t do it.  I’m not doing it!’  Totally understandable!  It is wise not to depart too far from what you know, and a good idea to verify a practice for several years before adopting it.  If Adapt-N comes up with an uncomfortably large sidedress nitrogen recommendation for your field(s) you can 1) still apply whatever level of sidedress N you are comfortable with, and/or 2) apply a the recommended rate to one or more small, typical, and visible areas of your field; 3) be ready to make further adjustments if the need becomes clear; and 4) do a stalk nitrate test at harvest to see which strategy worked better.

If you are curious about what recommendation Adapt-N would give for your field, please feel free to contact me.  I do have a license for the program and am running recommendations for interested farmers.  My main goal is to teach people how to use it so that they can begin using it themselves.  It really does not take much time.

Daniel Hudson
University of Vermont Extension
Agronomist and Nutrient Management Specialist
374 Emerson Falls Road, Suite 1
St. Johnsbury, VT 05819-9103
Office: (802)751-8307 ext 356
Mobile: 802-535-7922


About Daniel Hudson

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