What is in this article?:
- High nitrogen rates might not be the best strategy for your corn crop.
- Southern corn growers must consider their environment when applying nitrogen.
- It's important to know how much nitrogen to apply and when to apply it.
HIGH NITROGEN RATES don’t always equal high corn yields, especially in the South where weather conditions can be variable.
How much N and when
It’s important, says Larson, that growers know how much nitrogen the plant utilizes and when it utilizes it over the course of an entire season.
“We start off with very slow uptake, especially during the first 30 days. When the plant hits the rapid growth state – the V6 growth stage – which is about 18 inches tall, you need to have your nitrogen applied because that’s when the most rapid nitrogen uptake occurs during the season.
“You need to have a little bit of nitrogen applied early, either at planting or right after it comes up, using a number of different sources and application methods to apply it. You can even rely on a starter fertilizer to supply this first split because the corn plant utilizes very little nitrogen early, especially in the first 20 to 30 days.”
Just because you apply nitrogen doesn’t mean the soil will take it up, he warns. It’ll be in the soil and subject to loss. “You do need a little bit of nitrogen early, but you don’t need very much. You can even wait until the corn is up to a few inches tall.”
If you’re growing irrigated corn or applying more than 200 pounds of seasonal nitrogen, says Larson, you need to apply about 75 percent with the second split or sidedress application, at about the V6 stage.
“Timing might not be such a big issue, especially if we have a dry spring, or if you can get over your acreage fairly quickly. If it’ll take you 10 days or more to get over your acreage, timing can become difficult.”
Larson says he considers the pre-tassel nitrogen application as an additional split. “It won’t produce a yield response every year, and that’ll depend a lot on what happens earlier in the year.”
If you have extremely wet conditions during the season, this particular nitrogen application could be used to correct a deficit situation, he says.
“In that case, you may need to apply even more with this split. De-nitrification rates in the South can range from 2 percent per day when soil temperatures are less than 60 degrees to 4 to 5 percent per day when soil temperatures are greater than 60 degrees.”
Nitrogen deficiency is relatively easy to identify, says Larson. It will first show up on the leaf tip, with yellowing followed by browning.
“It’ll occur on the lower leaves in the crop canopy. The issue with using tissue analysis to determine nitrogen rates is that if you do tissue analysis at the vegetative stage or even up to tasseling, you’ve utilized less than 65 to 70 percent of your seasonal nitrogen, and you’d have to be in an extreme deficiency to show that the plant didn’t have sufficient nitrogen at that time. Even at tasseling, you’ve used only about 60 to 70 percent of your seasonal nitrogen.
Tissue sampling to me is more important for identifying a problem at the end of the year.”