Study Provides New Details On Managing Nitrogen in Wheat
Published: Mar. 12, 2008
URBANA-The recent high cost of nitrogen fertilizer and the high current price of wheat have had a major impact on the proper rate of spring fertilizer nitrogen application to wheat.
"Recent studies across the state have provided some important insights on the optimum economic nitrogen rate on wheat," said agronomist Steve Ebelhar from University of Illinois Extension.
The data provide the recommended spring nitrogen rate based on the nitrogen price, the wheat price, and the percentage of organic matter in the soil. The results are available on the Internet at http://www.cropsci.uiuc.edu/research/rdc/dixonsprings/pdfs/WheatNRateRecs08.pdf.
"In general, nitrogen rates decrease as soil organic matter increases," Ebelhar said. "This is due primarily to the nitrogen released from organic matter, along with a lower probability of nitrogen losses from the soils with higher organic matter."
On soils with more than 4-percent organic matter, the optimum economic nitrogen rates ranged from 56 to 62 lbs. per acre based on a nitrogen price of $0.60 and new-crop wheat prices between $7 and $8 per bushel. These rates would be spring applied to wheat in addition to the fall nitrogen rate applied, usually in the range of 20 to 30 lbs. of nitrogen per acre.
"The range was from 99 to 105 lbs. on soils with organic matter levels from two to four percent," Ebelhar said. "The range was from 145 to 150 lbs. on soils with organic matter levels less than 2 percent."
He notes that the nitrogen rates change within an organic-matter level as the ratio of the nitrogen price to the wheat price changes.
"At each wheat price level, the nitrogen rates decrease as the price of nitrogen increases," Ebelhar said. "At each nitrogen price level, the nitrogen rates move in the same direction as the wheat price."
Ebelhar points out that those recommendations are based on uniform applications of nitrogen fertilizers.
"If there is uncertainty about the uniform application of nitrogen, especially with spinner-type fertilizer buggies, then the nitrogen rates should be reduced by about 20 lbs. per acre in order to prevent over-fertilizing some areas," he said. "Be aware that this might well decrease the overall yield, since nitrogen is likely to be deficient in those strips with lower rates."
He adds that some growers may find it more cost-effective to hire someone to make the application in order to assure more uniform spreading.
"Using inhibitors and slow-release nitrogen products tends to increase the efficiency of nitrogen use by wheat by moving the release closer to the time the plant is taking up nitrogen," Ebelhar said. "This can reduce the nitrogen application rates, but, because there is no way to predict the nitrogen loss conditions, it remains difficult to know if these are cost effective, or even how much to reduce nitrogen rates."
Ebelhar notes that additional considerations can apply to some growers in southern Illinois on soils with low organic matter.
"Those who wait to apply their nitrogen until later in the spring or split apply their nitrogen in the spring with the majority of the nitrogen applied just before jointing, can gain some efficiency and should be able to reduce their nitrogen rates by 10 to 20 lbs. of nitrogen per acre," he said. "We did not see this same effect on the sites with high organic matter."