Farmers across the Corn Belt may be tempted to park their sprayers and hope for the best after a wet spring and record-high input bills. But Farm Journal Field Agronomist Missy Bauer warns that could be the costliest decision they make when it comes to their corn crop.
A mix of too much moisture along with stints of warm soil temperatures this spring opened the door to denitrification and leaching, Bauer notes. For those reasons, she believes corn growers can’t assume their original nutrient plan is still working.
“Maybe you had a great May and first half of June,” she says. “I think you still need to be probably pulling some nitrate samples to make sure that you’re not going to leave anything on the table with this crop.”
Nitrate Tests Require A Different Approach
For growers who decide to test, Bauer stresses that a soil nitrate sample is not the same as a routine soil fertility test. Depth of testing matters.
Standard soil samples usually go 6 to 7 inches deep. Bauer wants farmers to double that — and, where possible, to look even deeper.
“We want to go down into the soil and pull at least a full foot,” she says. “If you’re in an area that you could go back down the same hole and get the second foot of soil to test that would be ideal.”
Sampling the first and second foot can help determine whether N has simply moved lower or is largely gone.
“If it’s in that second foot, we’ll have opportunities to pick that up in the corn crop later in the season,” she says. “But if both feet are flushed, then we know we’re in real trouble.”
At the same time, Bauer acknowledges that high N prices have many farmers looking for places to cut costs. She urges diligence.
“Maybe you can cheat on phosphorus, or you can cheat a little on K, but you can’t cheat on nitrogen,” she says. “The crop needs a lot of nitrogen to push yield and push those bushels.”
She advises any grower who trims N rates to back up that decision with in-season nitrate tests and tissue samples, including around tassel, and to be prepared to respond quickly if numbers come in short.
Rapid Growth Stages Are Underway
Timing and N availability become even more critical as corn hits rapid growth stages, which is starting to occur across much of the Midwest.
“The bulk of your nitrogen — I’m not saying all of it — the bulk needs to be on by the time we get to about V8 to V9,” Bauer says, noting that from that stage to tassel, corn can take up 7 to 8 pounds of N per acre per day.
Banded applications — whether with coulter injection on smaller corn or via Y-drops — can help stretch N dollars, she says, particularly if the weather turns dry after decisions are made.
“We can be super successful with [Y-drop] even if it turns dry,” she says, because the band sits “real close to the base of the plant.”
Keep Sulfur Available, Too
Nitrogen isn’t the only nutrient Bauer worries about this season. With little sulfur (S) now coming from atmospheric deposition, she says wet weather and skipped preplant applications are combining to expose deficiencies.
“Sulfur is definitely a potential issue this year with the rains that we’ve had,” she says, adding that many growers dropped ammonium sulfate ahead of planting to save money and then “were just adding the extra N later.”
Rather than across-the-board cuts, Bauer encourages farmers to use variable-rate nitrogen to “move around nitrogen dollars,” pulling back on high-organic-matter low ground and feeding lighter, yield-limited hills.
Above all, she says, this is not the year to manage your corn crop from the road.
“Don’t walk away from your crop,” Bauer says. “Get out in your fields, do some evaluations of your crop so we know what we have to protect as we go through this season.”
