How to handle corn’s most costly input

Here’s a nitrogen-related question for this month’s Indiana Certified Crops Adviser panel.

I have 33,500 plants per acre in one field. That hybrid likes high population. I shot for 30,000 in another field but only got 25,000 due to wet weather. About 35 pounds were applied as starter. How much N should I side-dress in each field?

Steve Dlugosz, agronomist, Harvestland Co-op, Wayne County: Adequate nitrogen is essential for maximizing yields, even when stands may be a little lower than desired. Significantly reducing N rates on a thin stand could be costly, especially if future wet weather is an issue. I would sidedress a rate similar to the one you planned for.

Gene Flaningam, Flaningam Ag Consulting LLC, Vincennes: The high-population hybrid has the best yield potential. This field apparently hasn’t received the adverse weather conditions that can both reduce populations and available N from starter. Assuming the low population field has a flex-ear and would yield similar to the high-population hybrid, I would not change the N rate on these two fields. Check out the nitrogen rate calculator at extension.agron.
iastate.edu/soilfertility/nrate.aspx
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Willis Smith, Senesac Inc., Fowler: There are several more things we need to know, such as nitrogen and corn price. Beyond that, the old rule was 1.2 pounds of N per bushel, less credits after soybeans. So 200-bushel corn would need 210 pounds commercial N (200 × 1.2 - 30 credit = 210). If you had already applied 35 pounds, I would have recommended 175 more.

Recent data indicates N needs may be less than 1 pound per bushel. Use 0.95 pound here. If you shoot for 230 bushels in the 33,500 field, the equation works out to adding 153 pounds per acre.

All research indicates lower population requires less N. Simple math says the 25,500 field needs 76% of the 33,500 field, or 116 added pounds. If it’s a flex hybrid, add an extra 20 pounds. I would recommend 136 pounds per acre.

This article published in the June, 2011 edition of INDIANA PRAIRIE FARMER.