Nitrogen management tests indicate that excess nitrogen fertilizer not only costs more on the input side, but can also force a drop in yield.
The research, conducted by the Northeast Agricultural Research Foundation, or NARF, in Melfort, Sask., documented the economic impact of putting 100 pounds of nitrogen per acre on spring wheat. The test used 50 pairs of side-by-side plots. The control plots received no nitrogen while the neighbouring plots received a rate equal to 100 lb. per acre.
The overall economic performance of the 50 plots that received no nitrogen was significantly better than the 50 fertilized plots. The smallest economic loss on a fertilized plot was $28.24 per acre while the biggest loss was $63.95 per acre. The average loss caused by applying 100 lb. of nitrogen was $42.76 per acre or about $6,841 on a quarter section. (See table Impact of 100 lb. nitrogen.)
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The analysis was conducted on the basis of Canada Feed at $1.50 per bushel, nitrogen at 35 cents per lb. and fertilizer application costing $3 per acre. The plots, measuring one sq. metre each, were located on a north-south pattern over an 800 metre stretch in a field near Melfort. The variety AC Crystal was seeded on May 12 at a rate of 120 lb. per acre.
Nitrogen backfires
Depressed yield because of too much nitrogen is not news, said NARF project leader Dennis McIntosh.
“Nitrogen can prompt yield depression by increased crop lodging, disease development, delayed maturity or haying off,” the Melfort farmer said.
“Although not as well known or as well understood, nitrogen can also cause increased toxic loading on plant tissue. When we look at trend lines for the two plot groups, we see that nitrogen fertilizer marginally increased the yields on about 60 percent of the plots. But nitrogen fertilizer more dramatically reduced the yields on about 40 percent of the plots.”
When comparing the average yields of the two plot groups, McIntosh said there was an average net reduction of 3.1 bu. per acre when applying 100 lb. of nitrogen per acre. (See table Microplot wheat yields.)
Strip trials conducted by Omega Research on a number of farms in the Melfort area in 2004 also indicate that nitrogen’s positive contribution to yield may be overwhelmed by the negative impact of excess nitrogen, McIntosh said.
“The traditional view that we should just put on lots of nitrogen because it’s cheap may be more folly than fact, at least in northeastern Saskatchewan. High rates are often employed in the quest for killer grain yields, but these peak yields require near-perfect growing conditions. Those conditions do not occur very often.”
Unaccounted nitrogen
But even in the best growing conditions, much of the nitrogen that is already known to exist in the field or that is applied as fertilizer cannot be accounted for.
McIntosh called this the unaccounted nitrogen.
“This is the N which cannot be accounted for in the above-ground plant material once we have measured all the grain and non-grain matter.”
The scientific rating for putting an exact number on nitrogen is called nitrogen use efficiency, or NUE. It calculates the overall plant biomass and provides a measure of nitrogen inputs versus the output of the plant.
In the recent Melfort studies, the plots that received no nitrogen had a NUE averaging 62 percent, meaning 62 percent of the nitrogen can be measured as grain, protein, leaves and stalks, with 38 percent remaining unaccounted for.
Protein on the zero nitrogen plots averaged 10.2 percent.
The total grain and non-grain plant material in the 100 lb. nitrogen plots contained more actual nitrogen than the unfertilized plots, but their NUE was 37 percent, meaning only 37 percent of the nitrogen can be tracked as grain, protein, leaves and stalks.
Sixty-three percent of the nitrogen has disappeared. Protein on these 100 lb. plots averaged 10.4 percent.
Actual grain yield was lower in the 100 lb. fertilized plots than in the zero nitrogen control plots.
“The fate of the excess nitrogen that has disappeared from the soil nitrate balance equation is unknown,” McIntosh said.
“Small amounts of N might be accounted for in ammonium nitrate that we didn’t measure, that leached downward into the soil or subtle losses into the atmosphere. But the larger portion of unaccounted N escapes detection in our current soil testing procedures.”
GreenSeeker in action
Probably the most important tool in the NARF toolbox is the Green-Seeker RT500. This scientific instrument uses optical technology to measure in-crop NDVI values, an indicator of total above-ground biomass at the instant the reading is taken. The latest RT500 is self-illuminating, so it can provide accurate information regardless of sunlight conditions.
Using this real-time information, the operator can determine the nitrogen status of a growing crop. This information gives the farmer an indication of how appropriate various nitrogen rates might be at a specific time.
Armed with this information, a producer can make a precise assessment of nitrogen use that has already been applied to the crop and make better decisions about additional in-crop nitrogen.
In their quest for a better understanding of nitrogen management, NARF and Omega started using the GreenSeeker in 2003. With two years experience, members are now looking at how to employ the Green-Seeker on a large scale on their farms.
In one test field on Stacey Moskal’s farm in 2004, the GreenSeeker detected high nitrogen levels during the growing season, before the crop had headed.
The field had received 70 lb. of nitrogen. The GreenSeeker information predicted a yield reduction of three or four bu. due entirely to nitrogen toxicity. When the crop was weighed at harvest, it yielded three bu. less than the adjacent field that had received no nitrogen.
“There are a lot of farmers who spend a lot of money on nitrogen, only to have that nitrogen end up lowering their yields,” McIntosh said.
The in-field adaptation of Green-Seeker technology is similar to that of GPS technology in some ways, he added. Although GPS had been around for 15 years, nobody could find a viable use for it until it recently became obvious that the guidance aspect is more useful than precision mapping. In the last two years, GPS guidance has found its way onto thousands of prairie farms.
“I think GreenSeeker is already on that same threshold as GPS three years ago,” he said.
“It may soon become a viable on-farm management tool. But it won’t be as easy as GPS guidance, because it’s not something you can simply buy, plug in and let it start working for you. If you want to find out where your nitrogen is, you’ll have to commit some time to learn this technology.”
He likened it to learning to read.
“Once you’ve mastered the basics, there are whole new worlds of information out there that open up to you, information you could not possibly access before. It really seems like there’s no limit.”
Tailor-made info
Some wheat varieties make better use of nitrogen than others, which is one of the new worlds of information the GreenSeeker helped NARF members open up in 2004.
“GreenSeeker showed us distinct NUE differences that were based strictly on wheat variety,” McIntosh said. “This took us completely off guard. You might say we stumbled across it.”
He said the group hadn’t considered looking for a variety correlation, but the GreenSeeker made it so obvious that it couldn’t be ignored.
NARF’s members grow many different varieties of wheat and according to GreenSeeker data, some of these varieties consistently have better NUE numbers.
“This has huge implications for the economics of growing wheat on the Canadian Prairies,” McIntosh said.
“And it’s one more compelling reason farmers should challenge the industry focus on increasing yields by applying higher levels of inputs. Recommendations biased by soil nitrate values may be more misleading than they are enlightening.”
He had advice for farmers.
“First, question if high rates of nitrogen fertilizer are profitable. Next, on individual farms, get the real answers by doing a few simple strip trials using GreenSeeker and yield measurements. Then calculate the financial loss resulting from overapplication of N. Finally, nitrogen management should be refined to improve profit, not yield.”
