Plant now, worry about nitrogen later
Last year, it was too dry. So far this year, it's been too wet. The former condition likely means you still have some of that nitrogen you applied left in your fields. The latter means you're probably in a rush to get this year's crop in the ground.
It creates something of a bottleneck of uncertainty. First, you can't be certain how much nitrogen you have left out there, so you can't know how much to put down. And, you don't know how much your crop's going to need, as that depends a lot on conditions leading up to when you do eventually have a chance to put down more N.
So what should you do? "Regardless of how much nitrogen may or may not be present, if you have not planted your field yet, it will be more important to plant now and apply additional N later so planting is not delayed further," says University of Illinois Extension soil fertility specialist Fabian Fernandez.
Planting first and putting down more N second isn't just a good decision for the sake of getting the most out of your time this spring; research shows putting down nitrogen when the corn's a little bigger can give you more bang for your buck, says University of Missouri Extension agronomist Peter Scharf.
"“Delaying planting is more likely to hurt yields than delaying nitrogen application. Research shows that delayed nitrogen application won’t hurt yield," he says. "In wet years, delayed nitrogen application will actually help yields.”
Scharf says from 2008 to 2010, corn that got a shot of nitrogen when it was around knee-high got a substantial yield boost -- in some cases, by up to 60 bushels per acre.
"This is because the nitrogen applied at planting was lost due to wet weather and was not there when the crop needed it in June and July," he says of the wettest of those years studied.
What's the best way to know how much you need to apply? Fernandez recommends using a presidedress nitrate test later on this month or in early June once your crop is planted. This test can show not just how much nitrogen is present, but also how much potential your soils have for mineralization and subsequent N loss.
"This timing should work well to allow results to come back from the testing lab with ample time for a sidedress application. An additional advantage to collecting soil samples starting in late May is that the test provides a good reliable measure of N because the potential for N loss of all the N present in the soil is low by the end of May. Since soil temperatures are warm by then, the test will measure mineralized N from the soil organic pool in addition to other sources such as carryover N," Fernandez says. "The sample needs to be collected from the top 12 inches of the soil."
Ultimately, the more it rains this spring, the less of that carryover nitrogen will stay in your soils. If you do test and find substantial leftover amounts, you can help keep it there by using a nitrification inhibitor, according to Pioneer public relations manager Jerry Harrington.
"While N fertilizers such as anhydrous ammonia, urea, and urea-ammonium nitrate (UAN) exist in various forms, the basics of nitrogen availability still apply. Stable ammonium (NH4+) forms are gradually broken down into highly soil-mobile nitrate (NO3-) that readily leeches out of the soil profile. This breakdown process is known as nitrification. Nitrification generally occurs at soil temperatures above 50 degrees and increases as temperatures rise above this level," Harrington says. "Nitrification inhibitors such as nitrapyrin and DCD (dicyandiamide) are compounds that slow the conversion of ammonium to nitrate and have proven effective for this purpose."