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Time for an irrigated fertilizer agronomy update

Research will assess the nitrogen use of a range of crops, the best way to apply N, the value of coated urea and the impact of cutting back irrigation use with modern crops and technology.

March 5, 2008  By Helen McMenamin

The ‘facts’ underpinning basic agronomic decisions may not hold true for today’s farming. Much of the basic research was done almost 40 years ago, some is even older, dating as far back as the 1940s. New crops, new varieties and chemicals, more efficient technology, even
global warming have all changed farming, but growers still use some of the basic research done for outdated farming systems. Alberta Agriculture and Food research scientist, Ross McKenzie is leading a project that aims to update the underpinnings of agronomic recommendations.

McKenzie has set up trials of 11 crops, each with various nitrogen regimes under irrigation to assess nitrogen use efficiency with N applied as anhydrous ammonia, as banded or broadcast and incorporated conventional urea or ESN (Agrium’s Smart Nitrogen, a slow release fertilizer). The N will be applied in early or late fall or in spring immediately before seeding.

The crops are hard red, prairie spring, soft white and durum wheat; two row malt barley and six row barley for feed and silage; triticale for feed and silage, canola and flax. All are modern, high yielding varieties grown using today’s technology. The project involves almost 3000 plots at Lethbridge and is repeated at Bow Island.


The project also includes wheat, barley and canola at nine dryland sites across Alberta with urea, ESN and a 75:25 blend of urea and ESN broadcast and banded in fall and spring. ESN, with its protective coating, is not vulnerable to losses in cold or wet soil, so more N should be available to the crop later in the season. McKenzie suspects this will not translate into a yield advantage for these crops, or not enough of an advantage to justify the premium for ESN.

“It’s hard to justify an extra 12 cents a pound for ESN for basic crops unless there is a clear yield advantage or definite advantage to the environment,” says McKenzie. “My experience is that any yield benefit from supplying N during the growing season is small. But, late season N can increase protein. There may be an economic advantage. ESN may be useful for long season crops like potatoes or corn that usually need fertigation. We may get similar answers to those we got the last time this sort of work was done in the early ‘70s. But, it’s important to check whether all the things that have changed in the last 35 years have affected this basic information.”


It is too soon for McKenzie to see any trends. The team will likely spend much of the winter processing samples and crunching the numbers for the first year’s results. But, he expects banding N in the fall or spring to be the most efficient. “Fall fertilizing gives a big advantage by allowing you to start seeding earlier. Our results showing the yield increase and the crops that benefited from early seeding really surprised us.”

McKenzie’s work has shown yields of chickpeas, mustard, soft wheat and malt barley dropped an average of 25 percent with a 21 day delay in seeding. If seeding was delayed another two weeks, to late May in southern Alberta, crop yield potential dropped as much as 40 percent. “All these crops, even mustard with its reputation for heat tolerance, are cool season crops,” he says. “Early seeding allows them to complete their vegetative growth and perhaps flower earlier in the season before the stress of summer heat.

Alberta’s provincial oilseed specialist, Murray Hartman has found McKenzie’s findings extend to other crops and areas. He used crop insurance figures to link earlier seeding dates to higher yields in all major crops and areas of Alberta, even where seeding is often delayed due to cool soils. “Seeding into warm soils gives you faster germination, more even emergence and a better stand,” he says. “We believed that meant the best crops, but we’re changing our views. Early seeding, even if soil temperatures are only two or three degrees C, seems to give better yields.”

The only exceptions, according to Hartman, are frost sensitive crops like beans and buckwheat. Yields of these crops may be higher with early seeding, but there is more risk of frost forcing reseeding. Also, in southern Alberta where seeding can start in late March, delaying seeding until mid April had less effect and sometimes increased yields.
McKenzie’s project also has an environmental component, measuring nitrous oxide emissions at Lethbridge. ESN is being touted as more environmentally sustainable than conventional nitrogen fertilizer because it is less prone to loss through leaching or denitrification, which can lead to emissions of nitrous oxide, a greenhouse gas 310 times more potent than CO2.

Southern prairie soils are only wet enough for significant denitrification when early summer rains are very heavy, so McKenzie does not expect to find evidence of N loss. “Denitrifying bacteria need waterlogged soils so there’s no oxygen, high organic matter and high nitrogen,” he says. “Those are not common conditions on most of the prairies, but we’ll have to see if there are losses.”

The project includes research by Shelley Woods into water use efficiency of high yielding wheat and canola at Lethbridge and Bow Island. She is comparing yields and quality with ideal irrigation – soil moisture in the surface 40 centimetres of soil (16 inches) kept at 60 to 90 percent available water, with irrigation restricted to 75 or 50 percent of the ideal, and with restricted irrigation except during flowering.

Flowering is the critical period when yield potential is established, says Woods. After two seasons of the five year project, she sees signs that crop yield and quality can be maintained with restricted irrigation so long as ample water is supplied during this critical time. -end-


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