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Corn School: How much side-dress nitrogen does the crop need?

By: RealAgriculture Agronomy Team

June 16, 2022

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In Ontario, corn growers are approximately six weeks into the growing season and now is a great time to do a couple tests to reassess the nitrate levels and decide on what the best plan is to sidedress nitrogen, on a field by field basis.

Deb Campbell, agronomist with Agronomy Advantage, joins us for this episode of RealAgriculture’s Corn School and talks all about which tests should be done and how to go about testing fields to get the most accurate and usable information.

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For this episode, we join Campbell in a corn field that is very well established at the seven-leaf stage and says although it’s made good progress, the concern is now to provide enough resources to finish off the crop and ensure a satisfactory yield.

“This is a great window to reassess and and do a gut check on that nitrogen plan that we had in place. Do we increase it? Do we soften it a little bit? What’s the status of this corn today? It comes down to in a lot of cases, producers use that number of a pound of nitrogen per bushel of corn, and that’s still a good place to start,” says Campbell.

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Things to consider when reassessing includes if the crop is still on target to hit the yield potential that was set out at the beginning of the season, this along with moisture levels and how much nitrogen is in the soil currently. She says it’s really helpful to do tissue sampling of the plants and to do nitrate testing in possibly up to four areas of the field, depending on landscape.

“To do a nitrate test, and to do it well so that you have reasonable confidence in the numbers that you’re getting back. You want to take a 12 inch core in the field,” says Campbell.

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She adds that farmers will also want to consider how the field has been managed, strip till versus full tillage plus other factors. “If you’re running a high nitrogen starter, you maybe want to take a few more probes out of the row versus between the row and then look at the spatial complexity of the landscape. So those low slope positions may be higher organic matter, the knolls, where you’re lower organic matter, less moisture holding capacity, all of that comes together to influence your soil nitrate and your mineralization capacity of your field.”

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She says it never hurts to re-test your fields either. If you have a livestock manured field which tested high for nitrogen earlier on but you aren’t quite sure how those levels held out, Campbell says it’s best for your own peace of mind and for the yield of your crop to simply go out and re-test the nitrate levels in the soil as it sits today. Best case scenario, the levels are still holding high and worst case is they are below what you anticipated, but you now can make a well informed plan to get the needed nitrogen back into the soil.

For all the episodes of RealAgriculture’s Corn School, click here.