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Integrated Pest & Crop Management



AUTHOR

Peter C. Scharf
University of Missouri
Division of Plant Sciences
(573) 882-0777
scharfp@missouri.edu

Don't sleep on nitrogen

Peter C. Scharf
University of Missouri
(573) 882-0777
scharfp@missouri.edu

Published: June 19, 2020

On June 18, we've had a week of dry weather, and the wet spring almost feels like it's in the rear-view mirror.

But with a projection for above-normal precipitation over the next 10 days, there is potential for additional loss of nitrogen from corn fields that could push us over the edge.

map of midwest with vary colors and textures

Despite the dry week, large areas of Missouri (and Illinois, Iowa, Kentucky, and Ohio) are in the Danger Zones (above) for nitrogen loss. I think that we are poised to have a large problem with N loss if the last two weeks of June are wet, and there will not be a lot of time to respond. It will be important to have a plan in place for how to assess N loss and to apply additional fertilizer if needed.

A plan for how to apply additional fertilizer means knowing which machines can do the job, their cost, their availability, and your order of preference. Planes, high-clearance spinners, and high-clearance sprayers with large tanks are all increasing in number in Missouri. If you would hire this work done, reaching out now to the person who controls the machine(s) would be a good idea. By early July, planes will no longer be an option because they will switch to applying fungicide.

Assessing N loss is more difficult. If you're not in the Danger Zone at the end of June, you don't have to worry. If you are, aerial/satellite images can let you assess a lot of acres in a hurry. Call me if you want more information on how to do this. Deep soil samples are an option, but they should probably be 2 feet deep and require lots of cores if N was banded, so they are hard work and slow. Results can be interpreted using MU Guide G9177 probably until corn is hip-high. For farmers signed up for nitrogen models (Encirca, Adapt-N, Nitrogen Adviser), this is an easy way to assess N loss. If you're not signed up, my understanding is that it takes 20-40 minutes to enter the information for each field. This is not as slow as soil sampling, but is still an obstacle.

We've already had some nitrogen loss with the tropical storm remnants that swept up through the middle of Missouri a week ago. Especially in poorly-drained fields that stayed wet for several days, some N was lost due to the warm and wet soil conditions. And in well-drained soils, nitrate moved further down and possibly some moved out of reach of corn roots.

I expect that the amount of N lost so far has, for most fields, not been enough to make extra unplanned N applications profitable. But profitable yield responses to extra N on some fields (wetter than average, or more vulnerable due to soils or management) would not surprise me, even if no more N is lost. And for farmers who still have a planned N application to do, it makes sense to me to increase the rate if you're in the Danger Zone.

Most of all, if we get extra rain and more N loss, the stakes will go up and it will be crucial to be prepared, have a plan, and execute it.

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REVISED: June 19, 2020