RED DEER – While nitrogen is critical for wheat yields, it also affects wheat grain protein levels.
But Ross McKenzie, a soil fertility specialist with Alberta Agriculture in Lethbridge, said research suggests that adding an in-crop application of nitrogen to boost protein may not boost levels enough to cover the cost of the fertilizer and its application.
“We like to see the protein content of hard red spring wheat in that 12 to 13.5 percent range. As long as you’re over 12 percent, you’ve put on enough nitrogen to get optimum yield, but often you haven’t hit the optimum protein content.”
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He added that if a soil is deficient in nitrogen, yields will gradually increase as nitrogen fertilizer is added.
“Once we hit a sufficient level of nitrogen, we get optimum yield and it stays about the same in the sufficiency zone. If we add any more nitrogen, we might even see a slight dip in yield if we have too much nitrogen.”
When it comes to protein, McKenzie said in fields deficient in nitrogen, farmers could see a slight drop in protein content as nitrogen is added. However, the protein content will gradually increase.
“At optimum level for yield, we’re still below optimum level for protein. We’d have to continue to add nitrogen until we reached a level around 15 plus percent protein.”
Due to uncertain moisture conditions, growers usually apply only enough nitrogen for optimum yield. If they want to try for a higher protein content, they may choose to apply nitrogen later in the growing season, if weather conditions are favourable.
“The effectiveness of nitrogen application method to increase grain protein depends on the efficiency of the nitrogen uptake. Nitrogen fertilizer applied later in the growing season under dry conditions can be stranded.”
Ammonium nitrate 34-0-0 is not on the market for 2006, so McKenzie said urea is the only option for in-crop nitrogen fertilization. With liquid fertilizer, farmers can use a foliar spray or dribble band application. It can either be urea dissolved in water or urea-ammonium nitrate, the typical 28-0-0 UAN solution, he said.
“When we do a foliar application of nitrogen onto a crop, only about five percent of that nitrogen gets into the plant (through the leaves). Ninety-five percent is washed into the soil by rain and is taken up by the roots. So if you put on 20 pounds of nitrogen foliar applied, only one lb. would enter the leaves, while 19 lb. would be taken up by the roots.”
Foliar application of urea or UAN to boost protein in wheat has been tested in research trials. In Kansas, McKenzie said the spray application of urea at flowering was shown to be the most effective application stage for increasing grain protein in hard red winter wheat.
“They increased grain protein levels by 0.25, 0.75 and 1.4 percent with rates of 10, 30 and 50 lb. per acre. If you’re going to bump it up by more than one percent, you’re going to have to go to these higher rates,” he said.
In a two-year study in Manitoba, with foliar-applied urea or broadcast ammonium nitrate, applied 10 or 11 weeks after seeding at a rate of 30 lb. of actual nitrogen, grain protein was increased in a year with high yields, but not in a year with low yields.
In the year with low yields, there was already enough nitrogen to achieve optimum protein. In-crop application served no useful purpose, McKenzie said.
With these results in mind, a group of agricultural researchers co-ordinated a series of tests on in-crop nitrogen applications to boost wheat protein in hard red spring wheat, with co-operators from Brandon, Melfort, Sask., Lethbridge and Edmonton.
“In the study, we applied nitrogen in-crop at tillering, at boot and anthesis, with broadcast AN and foliar applied 28-0-0 solution. We worked with a rate of 15 lb. of actual nitrogen per acre. We were told that most farmers wouldn’t want to go with a rate much higher than 15 lb. Over 20, you run the risk of crop burning in some conditions,” said McKenzie.
Over a three-year period from 1997 to 2000, McKenzie had 11 sites in southern Alberta, eight in central Alberta, two in northeastern Saskatchewan and five in Manitoba.
The sites used a range of base nitrogen fertilizer rates, with urea banded at 0, 60, 75, 120 and 135 kilograms per hectare. At the 60 and 120 kg per ha rates, additional nitrogen was added at 15 kg per ha, at the tillering, boot and anthesis stages, by broadcasting AN and with foliar applications of UAN.
“At half the sites, the 60 rate of nitrogen gave us optimum yield already. At these sites, it would have served no useful purpose to put on any more nitrogen fertilizer,” he said at a recent conference in Red Deer.
When comparing the 60 kg rate with 15 extra kg of nitrogen to the 75 kg rate applied in a band at seeding, McKenzie said: “Most of the time, there was either no benefit or only a slight benefit with the extra 15 kg, in terms of increase in grain protein concentration.”
“We found that the in-crop application only increased grain protein at six out of the 26 sites. So not very often were we getting responses to 15 lb. of in-crop application. And only one site with in-crop application increased grain protein when compared back to the extra 15 lb. of seed-placed fertilizer.”
McKenzie said the average increase on the six sites that did increase was 0.3 percent of grain protein concentration.
“With the six sites that we had a response, there was a difference in method of application at four of those sites. UAN foliar applied was more effective at three of the sites and broadcast AN was more effective at one. But when it came down to differences in grain protein content, the UAN averaged out at 0.34 percent and the AN was 0.31 percent, so very little difference between the two.”
Eight of the 26 sites showed a difference in terms of timing of application. Of those, applying nitrogen at tillering showed a 0.2 percent increase in grain protein content, applied at boot stage was 0.34 and at anthesis or flowering stage, it was 0.4 percent.
McKenzie’s conclusion was that an in-crop application of 15 lb. of nitrogen did not economically increase grain protein of hard red spring wheat.
Based on current nitrogen prices and protein premiums, adding 15 kg per ha at anthesis provided a positive economical return at only five of 26 sites, assuming no increase in yield. On average, the cost of additional nitrogen was $4 more than the increased value of the grain produced.
“And as nitrogen fertilizer prices go up, it will become even more challenging. Probably one factor responsible for the small increase was that we were only working at rates of 15 lb. Perhaps we should have gone to higher rates, but if we did that, we would have had to dilute the solution, because one of the problems with high rates is you start to get leaf burn,” he said.
“Increases in grain protein were small, relative to the low basal rate of additional nitrogen and the general sufficiency of the rates we were working with. In general, broadcast AN or spray-applied UAN will increase grain protein content, but they weren’t more effective than just putting that extra fertilizer on at the time of seeding. But in-crop nitrogen application might be more effective if it was applied under more nitrogen-deficient conditions.”
