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• Speaking to a group of Alabama crop consultants recently, Jac Varco said rates, timing and placement of nitrogen fertilization all are important considerations when producing corn.
“But when we got in the middle, nitrogen use efficiency dropped because we’re placing it farther away from the plant. This past year, with surface dribble, we also saw declines as we got farther out.”
When researchers looked at yield influenced by irrigation, it went from 160 bushels per acre down to about 135 as the nitrogen got farther from the row and it was placed in the soil, he says.
“That’s 25 bushels, and a lot of money at today’s prices. There’s a general decline with the surface placement. Even though it’s out in the middle, irrigation washes it into the soil, but the band is already 3 to 4 inches deep, giving it a head start. This is all furrow irrigation on every row.”
In 2012, yields dropped off by 40 bushels from a high of 220 bushels per acre when it was applied closer to the row, says Varco.
“One factor too is that today’s varieties are yielding much better than in the past. There has definitely been a yield boost. If you’re banding your fertilizer, this research is telling us to get it closer, even to go from broadcasting to banding the UAN.”
Another study looked at tracer fertilizer and the recovery of nitrogen, explains Varco.
“With nitrogen surface-banded, we saw a decline in recovery and use efficiency goes down by about 15 percent. So we recover about 15 percent less of the fertilizer that we put out by going closer to the row.
“That tells us the corn roots aren’t always getting the fertilizer. In 2012, recovery declined by almost 20 percent when we got farther away from the row. The closer you get that nitrogen to the row, the greater the efficiency.”
In a study conducted on cotton, Varco says about 36 percent of the ammonium nitrate applied was recovered while 20 percent of the urea was recovered.
“When we put in Agrotain, the recovery was almost equal to ammonium nitrate, at 32 percent. UAN banded, about 9 inches from the row, was most efficient. There is some loss when UAN is applied surface-dribbled. UAN dribbled with Agrotain is as good as UAN banded.”
When growers are spending 40 percent of their crop input costs on fertilizer, they’ve got to find a way to maximize the efficiency, says Varco.
“What other input produces a growth stimulus as great as fertilizer nitrogen? Irrigation does, sometimes, and it costs a lot.
“The boost we get from fertilizer nitrogen is tremendous, so strategic application can make a difference. If it’s in the bed or if it’s flat ground, get it about 6 or 8 inches from the row, and it doesn’t have to be too deep.
“It’s important to split applications, anywhere from about 25 percent at planting and get the rest on by V7. Put your nitrogen out and then water it in, but don’t do a heavy irrigation. Just get the nitrogen into the soil, about one half inch. Our center pivots run about 7/10 inch, and one pass is a pretty good break.”
Growers might consider variable-rate application, says Varco, and the use of inhibitors should be on a case-by-case basis.
“If you really want to buy fertilizer insurance every time you plant a crop, then you should use an inhibitor. But I believe it should be on a case-by-case basis, considering the conditions.”