LETHBRIDGE – Grain farmers are restricted in the amount of seed row nitrogen they can apply without damaging germination and thinning plant stands.
However, with the loss of ammonium nitrate, fertilizer companies have started introducing new technologies to slow the release of nitrogen.
One aspect of these products is that more nitrogen can be applied in the seed row than with untreated urea, allowing direct seeders an opportunity to place higher rates with single-shoot seeding systems.
Stu Brandt, an Agriculture Canada researcher in Scott, Sask., recently completed a project looking at Agrotain-treated urea and ESN, a polymer coated urea produced by Agrium. Both products slow the release of nitrogen and allow farmers to apply higher urea rates in the seed row.
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Brandt worked with conservation research groups in Swift Current, Canora and Redvers in Saskatchewan.Studies were held in four soil zones: one in the brown; one in the dark brown and two in the black zone.
“With direct seed systems, we want to be able to put all the fertilizer down at the time of seeding,” Brandt told the recent Agronomy Update in Lethbridge.
Slow release treatments included untreated, seed-placed urea; Agrotain-treated, seed-placed urea; seed-placed ESN and a sideband treatment.
“One other option we wanted to look at in the study is whether we could place some at the time of seeding, then top it up with liquid fertilizer later on in the growing season,” Brandt said.
“That liquid fertilizer, we planned on putting it on three weeks after seeding, but some of the locations were as much as five weeks after seeding because of moisture conditions.”
With wheat, the study used 25 kilograms per hectare of urea as a base rate. That rate was established based on safe rates for a 10-inch row spacing and a one-inch spread of seed and fertilizer within that row.
“The suggestion was with Agrotain we could safely seed place up to 50 percent more – 37.5 kg per ha. We then increased that to 50 and 100 kg per ha,” he said.
“The split applications where we were looking at liquid fertilizer, we were applying the same four rates, but in the first case we placed zero fertilizer and all the nitrogen was dribble banded. The second rate with no fertilizer seed placed and the 37.5 kg rate dribble banded. Then we placed 25 with the seed and 25 dribble banded. With the 100 kg rate, we seed placed 25 kg and dribble banded the remaining 75.”
At the dry sites, the researchers found a reduction in wheat emergence with untreated urea, even at low rates.
“The reduction was large when you got to the high rates of untreated urea. We saw a similar reduction, though not as severe, with Agrotain-treated urea,” Brandt said.
“With the polymer treatment, we didn’t see any reduction in plant populations until we got to the highest nitrogen application rate, and the reduction of plant population was relatively minor. Sideband had no effect.”
Researchers didn’t find yield differences between the different forms of urea and urea treatments until they reached the highest application rates.
“In that case, both the Agrotain and untreated resulted in yield losses compared with sideband. The polymer provided yields that were equivalent to the sideband treatment.”
The researchers also ran a duplicate study with canola in Scott in 2004.
“We used lower rates because canola is more sensitive to seed-placed nitrogen. We could only safely seed place 10 kg per ha of untreated urea with that 10-inch row spacing,” said Brandt.
“We did see a significant reduction in plant population, with both Agrotain and the untreated urea, compared with side band or seed-placed ESN. But it’s important to keep in mind this is a crop that has a large capacity to compensate for low plant population.
“We know that as long as plant populations don’t drop below about 50 plants per sq. metre, the crop will compensate for reduction in plant density and there’s a minimum impact on yield. So it wasn’t a big surprise that the form or placement had minimal impact on canola yield.”
Brandt said moisture levels play a large role in crop safety with seed-placed nitrogen, but the split application parts of the trials revealed interesting observations.
In the wheat site at Swift Current, which was low in nitrogen, Brandt found with the split nitrogen application, the plots were short of nitrogen early in the growing season. Even after top dressing was applied, it was too late for the crop to fully recover.
“In 2004 at Scott, with a higher N supply from the soil, we didn’t see the same deficiency showing up. Under those circumstances, the liquid split application worked as well as sideband,” he said.
In Canora, with wet conditions, the split application at the highest rate resulted in higher yields than the sideband application.
“I suspect with the sideband application we were probably losing a bit of nitrogen, with saturated soil conditions throughout much of the early part of the growing season.”
The study concluded that when soil conditions are dry, any amount of seed-placed nitrogen should be approached with caution.
“Agrotain allowed for about a 50 percent increase in the safe rate of seed-placed urea in these studies. The polymer coated ESN has the potential to increase that rate by up to four times what we would consider safe with untreated urea,” said Brandt.
“There’s no evidence that Agrotain or the polymer delayed N uptake excessively. And seed placing the safe rate, followed by dribble banding of additional nitrogen, may be another option worth looking at.”
Brandt said the study is limited in scope, and to better understand nitrogen applications, factors in the trials would need to be broadened.
