A big question on the minds of corn growers this year, especially considering rising costs, is how they can be more efficient in their use of nitrogen.
“Unfortunately, when you use the word ‘corn,’ you have to use the word ‘nitrogen’ in the same sentence,” says Ron Heiniger, crop system specialist with North Carolina State University. “They're hand in hand, and it's difficult to make decisions about nitrogen and corn production without having some effect on yields.”
Environment, timing and rates all are important factors in nitrogen use on corn, says Heiniger. “Environment makes a key difference. When you have high-production, irrigated corn on good soils, and you're getting yields up in the 200-bushel range, you can be very efficient with nitrogen, even hitting a ratio of 1 pound of nitrogen per bushel of corn,” he says.
On the other hand, if your soils aren't productive, you won't get the full value from that nitrogen, he adds.
“As a result, you might be looking at a ratio of 1.5 pounds of nitrogen to the bushel of corn. Keep in mind that limiting factors in the environment will drive the efficiency of the nitrogen,” he says.
Turning to the timing of nitrogen applications, Heiniger says nitrogen has been tried on corn all the way up to the tasseling stage. “Believe it or not, we can recover yield up to that point. As long as the plant started with good fertility, we can wait with that nitrogen and still recover yield,” he says.
Almost 40 percent of the total nitrogen is taken up by the corn plant once it reaches silking, he says, and that's an opportunity corn producers may miss at times.
Early timing includes applying nitrogen out front, whether it is as starter fertilizer or adding to or supplementing the starter with more nitrogen.
“If you're growing corn on sandy soils, you think about how much you're going to lose in this situation. We have data that proves the importance of starter fertilizer in achieving a high-production crop and in getting maximum-use efficiency from your nitrogen,” says Heiniger.
Early nitrogen, he says, contributes to the early root development of the crop. “We often see a little difference in upper plant growth. What you don't see is what is actually making or breaking your corn crop — the root development.”
Factors that affect early root development include good early growth and vigor, good drainage, adequate nitrogen from germination to growing point, and proper placement, he says.
“Early nitrogen can have an impact. Often, we don't see that impact on actual root development.”
The early root system that grows from the seed is called a radical, says Heiniger. It basically is the taproot of the plant, and it only lasts for about six to eight weeks.
“In the past, we've had a somewhat negative view of how much that contributes to early plant growth. It certainly gets the plant up and started. But we haven't looked closely at how much it improves our yield.”
Research has shown that the early growth of the radical can have a significant impact on productivity, he says, and that means early fertilization.
The seminal roots, explains Heiniger, are the primary roots seen in a corn plant. They often are credited with the growth and productivity of the crop.
“That's the root system we really count on and really want to develop. We want a good, early root growth that contributes to a lot of seminal roots.” Research from various trials in North Carolina have looked at the impact of the early root system and its contribution to yield, he says. Trials included 15 and 30-inch rows with high plant populations. The root system becomes a critical issue whenever you go to high plant populations, he adds.
Trials looked at both no starter fertilizer and 19-19-0 applied in a 2 by 2 band, he says. When no starter fertilizer was used, the central core of the root system was devoid of the radical. Where starter was used, there was still root growth, says Heiniger.
“Not only does it put that root deeper, but it also contributes to the health and the prolific growth of the seminal roots in that system.”
In a trial with three different treatments — 19-19-0 with 30 pounds of potassium broadcast over the top, 19-19-0 alone, and no starter fertilizer — researchers excavated the corn plants, washed them, and measured the length of the root system and the root volume, he says.
There also were two different plant populations in this experiment, one being a high-plant population.
“There's a significant difference in root depth, particularly with the higher plant population. Adding potassium helps, and 19-19-0 was significantly different from no starter fertilizer in terms of root depth. It didn't make a huge difference whether or not you applied potassium, but both starter treatments were better than no starter. Anytime you can get that rooting depth, it contributes greatly to root volume.”
Plant population can make a big difference in production, says Heiniger. “In North Carolina, we've seen a lot of problems in our high-population systems, including lodging and nutrient deficiencies. The bottom line is that starter fertilizer does contribute significantly to yield at those high populations.
“We didn't see as big a difference in yield between the 19-19-0 and no starter fertilizer at the lower populations. We probably achieved better root mass and volume because we didn't have as many plants. Plants appear to compete with one another for space, nutrients and light resources.”
Timing becomes a factor in a highly productive corn crop with a well-developed root system, he says. “This contributes to your efficiency because any time you have higher yields, your overall efficiency is going to be better. The starter treatment is contributing to higher productivity in that system. Therefore, your layby nitrogen is better utilized, and you get more productivity out of the entire system by having this early timing.”
It doesn't always contribute to yield, he adds, but it does contribute to the productivity of the system.
There are different methods of making this starter application, says Heiniger. North Carolina researchers looked at three — a 2 by 2, in-furrow, and a broadcast. The 19-19-0 starter was put out at 4, 10, 20 and 40 pounds.
“It's fairly clear that the problem with in-furrow in relationship to corn yield isn't that the nitrogen doesn't contribute to a healthier plant, but that emergence is delayed. That was consistent in our studies.”
With broadcast applications, there wasn't a great difference between no starter fertilizer and a small amount of starter, he says. “From our data, it looks as though a 2 by 2 band is the most efficient way to capture that early growth.”
Many growers, says Heiniger, ask if it's worth the cost to make an early fertilizer treatment. “We've done starter comparisons since 1998, whether it be row spacing, plant population or placement effects, and average yields over those years increase by 12.2 bushels per acre when you use a starter fertilizer. If you figure corn at $2.50 per bushel, and if you figure 10 gallons of 19-19-0 at $15 per acre, we're getting a return of about $7 from that starter fertilizer.
“That's what we're seeing in North Carolina. And to a large extent, It think it's contributing to early rooting, and that's where we're seeing the real impact of starter fertilizer.”
Many growers want to know if they should put out more nitrogen early, or if they should put out more at sidedress, says Heiniger. Over a four-year period, researchers in North Carolina looked at how much nitrogen should be applied at planting. They looked at different rates of nitrogen at planting versus nitrogen at layby.
“Typically, we found that about 50 pounds of nitrogen need to be placed sometime around planting time. That's what we found over all of those years, with irrigated or dryland corn. But the critical point we need to make is that as layby applications are delayed, more nitrogen then is needed early. We often miss that in our corn production systems. The longer we delay our sidedress, the more important it becomes to have that early nitrogen in the system.”
Other research looked at layby nitrogen applied at two different stages of the corn plant — V7 and V14, or 20 and 50 days after planting. Nitrogen also was applied at planting.
“If we came back and put on 50 pounds of nitrogen at V7, we could reach our optimum yield level. If we waited until V14, 100 pounds of nitrogen were required to reach that same plateau. We recovered yield, but it took more nitrogen to do it.
“You can probably get by with less than 50 pounds if you come in earlier than V7. But if you're going to have a delay in getting on your layby, you need to have more nitrogen up front. It's critical to understand when you'll be doing your layby application.”
Researchers have looked at making split applications of nitrogen compared to applying it all at planting, says Heiniger. This was done in 13 tests.
“There actually was a significant difference in only two of the 13 years. But the overall trend was that a split application was better than preplant by about 7 bushels per acre. If you cost that out, it's probably worth it to come back and put on sidedress nitrogen.
“In general, if you're going to put it all on at one time, sidedress is better than at planting. This gives away some of the early growth, and you're giving up some yield potential in that situation.”
Turning to nitrogen rates, Heiniger says researchers have 21 site years looking at nitrogen use efficiency as it relates to the amount of nitrogen applied.
“What we've found over those 21 site years is that 145 pounds of nitrogen, on average, is our optimum rate. There was an average yield of 135 bushels per acre, so our nitrogen use efficiency was 1.08 pounds of nitrogen per bushel of corn. That's probably a good target for growing corn in a dryland situation.
“But that isn't the same in all years.