Current winter wheat nitrogen (N) recommendations in Ontario are a little behind the times. Based on 30-year-old research, the recommendations do not take into account such considerations as the significant changes in production practices, the potential for increased yields through the use of better genetics and the availability of fungicides and growth regulators.
New research on N response conducted by the University of Guelph (U of G) and the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) is changing that. And the work is helping to develop new tools for Ontario farmers to use to help them maximize their winter wheat yields; namely a new agronomy guide with updated N recommendations and a N-rate calculator that will include selections with or without fungicide.
The first results being used for these tools come from field trials led by David Hooker, field crop agronomist and assistant professor with the department of plant agriculture at the U of G, on soft red winter wheat (Triticum aestivum L.) from 2008 to 2010.
Hooker and his team looked at interactions among three fertilizer N rates, eight fungicide application strategies and various cultivars grown in nine fields across southwestern Ontario.
They found that cultivar, N rate, fungicide strategy and interactions among N rate, fungicide and cultivar significantly affected wheat grain yield. The results indicated there is potential for farmers to increase wheat performance by increasing N and using fungicide application strategies, particularly in some cultivars and in high yielding environments that may be favourable to disease development.
Concurrent to Hooker’s small plot research, 52 field scale trials were conducted by OMAFRA cereal specialist, Peter Johnson, and Shane McClure, a research lead with the Middlesex Soil and Crop Improvement Association. Doing field scale trials at the same time as intensive small plot work was a new approach, and proved to be a significant step forward in grower uptake. By the end of the three-year project, many producers had already adopted this new production technology.
Following up on these initial results, further trials by Johnson and McClure from 2010 to 2013 looked at the maximum rate of N applications on winter wheat under current management practices. During these trials, they applied N rates ranging from zero to 180 pounds per acre to generate N response curves and determine the maximum economic rate of N (MER-N).
The only variable that changed at each site was the N rate. All other variables remained the same following the producer’s normal production practices. Serendipity prevailed: at seven of 35 sites the grower did not get their fungicide applied. This “mistake” led to some interesting findings.
Yields “hit the wall” when 90 pounds of N was applied. However, this was only the case at the sites where no fungicide had been applied.
“We started looking at the difference in response when fungicide was applied and, lo and behold, there was a significant difference,” Johnson says.
What these follow-up studies indicated was that without fungicide, 90 pounds per acre was most economical; but with fungicide, there was an additional 6.1 bushels of yield response at 120 pounds of N. By increasing to 150 pounds, they gained another 3.6 bushels, although this added only a small increase to the bottom line. In 58 per cent of the trials where fungicide was applied, 150 pounds of N per acre was the most profitable.
“That’s way above what I ever would have anticipated,” Johnson says. “Whether or not you spray fungicide is significant in N response.”
Fall N application
While they were at it, Johnson and McClure included additional treatments at some of the sites to evaluate the impact of fall N on wheat yield and economics. Johnson says the data is clear: there is no benefit to applying N on winter wheat in Ontario in the fall.
“Most growers use a phosphorus fertilizer in fall that has four to 12 pounds of nitrogen in it,” he notes. “That is all the wheat plant can use in the fall. More than that is a potential environmental concern because the crop can’t use it, it’s there over the winter and might move off site. No fall nitrogen should be applied on wheat.”
Research continued to study N and fungicide interaction in 2014 and will continue for two more years to help with the development of the N -rate calculator. Further research will examine the relationship of split N, growth regulators, planting dates, and new fungicides and their response to N rates.
July 10, 2015 By Trudy Kelly Forsythe