BRANDON – Manitoba farmers have become increasingly suspicious of fertilizer guidelines based on conventional soil test procedures and data from old field studies.
They often say the guidelines don’t seem relevant to their yield levels.
There’s a good reason for this suspicion, says John Heard, a soil fertility specialist with Manitoba Agriculture.
He said there’s been little new research put into guidelines since the Manitoba Soil Lab was sold in 1992.
Now Manitoba Agriculture has started using Viterra’s database and that company’s up-to-date data.
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“This has allowed us to revisit some of the major crop recommendations for Manitoba and develop new response curves that are more appropriate to modern conditions. They’re more real,” said Heard.
The pattern Heard and his team are following to develop new guidelines is a departure from the conventional yield-oriented formula.
He said profit is the main force behind the new system.
“We’re going away from a yield goal model and instead adapting an economic model for fertility guidelines. We’re doing two things at once. While we’re modernizing the data set, we’re also switching over to a profit-oriented model for fertilizer guidelines.”
In the past, Heard said many recommendations were based on rotations with cereals only and with conventional tillage. Many crops grown today weren’t included.
As well, he said about half of the old trials were conducted on summerfallow with deep tillage, a practice that is long gone.
The new system is based on continuous cropping, direct seeding, a variety of crops and new technologies.
“We’ve observed that the yield responses for cereals have gone up in recent years, at least on soils with good moisture,” he said.
“So it’s important that we start to understand these new response curves in making fertilizer decisions.”
He said farmers can maximize financial returns by paying attention to the area on the curve where they see the biggest difference between gross returns and costs.
For example, calculating nitrogen on canola includes a window of about 20 pounds per acre around the optimum rate. If a producer applies nitrogen within that range, Heard said, that’s about as close as he’ll get.
With the new guidelines, a producer can select a range of rates based on his willingness to take risk.
Heard said comparing new canola guidelines to the historic guidelines finds the rates are similar if producers aim for a modest yield goal.
However, close study reveals subtle differences. Base yields have increased in unfertilized control plots, partially because of hybrids and better genetics but also because cropping systems have improved.
“When producers had fallow and tillage in the system, they probably had less in-season N release from organic matter,” he said.
“This N helps meet the needs of the crop, but it’s not measured in the soil test. We suspect our cropping systems today give us more benefit from the residue.”
For its part in the project, Viterra, formerly Westco, crunched numbers from more than 250 nitrogen soil studies. In the process of making sense of those studies, Viterra agronomy manager Rigas Karamanos took into account most soil and climatic conditions typically found in Manitoba.
All relevant Manitoba data relating to wheat, barley and canola yields, nitrogen applications and soil conditions have been entered into this new Nitrogen Calculator, which is available on Manitoba Agriculture’s website as an Excel spreadsheet.
The database for canola was not as large as for cereals, so yield response has not yet been segregated into distinct soil moisture categories. Most canola trials were conducted in favourable soil moisture conditions.
Producers can use the Nitrogen Calculator, profiled in the April 30 edition of the Western Producer, to run different scenarios, plugging in their own farm data for average yields, soil moisture and residual soil nitrogen, which is depicted in yellow cells.
The user has the option of changing fertilizer sources, costs, commodity prices and nitrogen rates.
In an instant, the calculator provides feedback on the economic consequences of applying nitrogen at different rates. As the producer uses the calculator to change crop prices and nitrogen costs, the optimum nitrogen rate also changes. The scenario with the maximum return to nitrogen is highlighted in blue.
Agronomists and scientists reviewed and tested the calculator this winter. The Manitoba Soil Fertility Advisory Committee approved it for public release March 17.
“We didn’t want to release it until we were sure we got it right,” Heard said.
” It’s like a fine home-made wine. It’s not very good if you uncork it too soon.”
The new guidelines can be accessed by typing Nitrogen Calculator into the search box in the upper right hand corner of Manitoba Agriculture’s website at www.gov.mb.ca/agriculture. The calculator works best if downloaded to a farmer’s own computer.
For more information, e-mail Heard at jheard@gov.mb.ca.
