Ohio State University recommends applying nitrogen between green-up and Feekes Growth Stage 6 (early stem elongation), which is generally the latter part of April. The potential for nitrogen loss will decrease by waiting to apply closer to Feekes 6; however, when we reach greenup, a common sense approach would suggest applying when field conditions allow application equipment, particularly since days available for field activities may be limited between greenup and Feekes 6. Having that green, actively growing, plant in the field does help in holding nitrogen in place.
We still suggest following the Tri-State Fertility Recommendations for N rates in wheat. This relies on the yield potential of a field. Once you have set a value for your realistic yield potential, the recommendation may be based on the following table for mineral soils.
Nitrogen rate for wheat by yield potential.
Total N rate
* 120 is the highest recommended rate.
We do not give any credit for the previous soybean or cover crop, since we do not know if that organic N source will be released soon enough for the wheat crop. The Tri-State Fertilizer Recommendations suggests that you subtract from the total (spring N) any fall applied N up to 20 pounds per acre.
When do we need to apply nitrogen to corn?
Even though we promote the Tri-State Fertilizer Recommendations as the tool for setting rates for P and K, not so with nitrogen. Even at the time the Tri- State Recommendations were written the philosophy on N was changing. Today we no longer recommend nitrogen rates based on yield goal. Recommendations today are based on economics and research trials to mange this nutrient.
The current tool for nitrogen recommendations in Ohio is the MRTN web-based calculator. MRTN (for the Maximum Return to N), also suggests the most profitable N rate: http://extension.agron.iastate.edu/soilfertility/nrate.aspx. The current recommendation for Ohio with a corn-soybean rotation is about 160 pounds of N per acre. Please go to the website and run your own scenarios. If you read the Tri-State Fertilizer Recommendations for N rates you see there are some efficiencies that can be gained and should still be valid today. I like these tips:
- For inadequately drained soils with high denitrification potentials, N should be either: applied in a split application; applied as anhydrous ammonia with a nitrification inhibitor; or concentrated in a band to minimize soil contact.
- Corn grown on coarse-textured/low CEC soils with high leaching potentials may benefit from split or multiple N applications.
- For soils with greater than 30% residue cover, the majority of applied N should be either: injected below the soil surface; dribbled in bands using N solutions; or broadcast only if the material contains no urea (i.e., ammonium nitrate or ammonium sulfate).
- No-till corn, corn planted into cold, wet soils, corn following anhydrous ammonia applied less than two weeks prior to planting, and corn following spring-tilled legumes or cover crops should receive some N at planting — 20 to 40 pounds of N per acre banded near the row.
Many of these conditions apply to Ohio soils, so almost every field can benefit from a split N application.
And when do we need nitrogen for corn? Some recent work at the University of Illinois shows that corn really doesn’t need much N until well into the growing season. This chart from an article on the www.ipni.net website, titled “Modern Corn Hybrids’ Nutrient Uptake Patterns”, shows when and how N is used by the plant throughout the growing season.
This work shows that we can get to V8 or later without a lot of nitrogen. A delayed application of N is more efficient, and less likely to be lost. Lost N costs the farm money, and becomes an environmental concern.
Take action on weeds
The United Soybean Board has developed some very nice materials to fight resistant weeds. Mark Loux our Extension Weed Specialist supplemented and printed several thousand of these packets for Ohio – they have been very popular at our winter pesticide re-certification training programs. The campaign to manage resistant weeds is called “Take Action” against herbicide resistant weeds. The website to get more information is http://takeactiononweeds.com. I especially like the Site of Action chart: http://takeactiononweeds.com/understanding-herbicides/site-of-action-lookup/.
There are no new herbicides — not quite a true statement, as there are many new names — but it is the active ingredient that is important, the rest is about marketing the name. So the site of action chart will help determine the active ingredient in the commercial product. I still remember as we were discovering the resistant marestail across Ohio, a farmer told me he had the solution to his marestail problem. He had been using “Roundup” until he learned it didn’t work any more — so he switched to “Buccaneer.” Only to learn that Buccaneer has the exact same active ingredient as Roundup. This chart will help avoid those mistakes.