Fall surface N robs canola of $180 per acre

It may be convenient to fall broadcast N on your canola acres, but that convenience can cost up to 18 bushels per acre

After decades of research proving that deep banding reduces nitrogen loss, farmers are resurrecting the largely abandoned practice of surface-applying nitrogen in the fall. But there’s a high price to pay.

In canola, that price is extracted in bushels per acre. Potential canola yields were slashed by 18 bushels per acre when test fields received surface-applied nitrogen in the fall. The study compared surface-applied to banding and spring broadcast.

When researchers looked at spring-applied surface nitrogen, canola yield was cut by as much as five bu. per acre compared to banding. That five bushels added to the 15 bu. for fall broadcasts equals an 18 bu. loss. If canola is 10 dollars per bu., the convenience of fall broadcast can cost up to 180 dollars per acre in lost yield.

The Manitoba research, originally published in the Canola Digest Science Edition, found that nitrogen source did not affect yield, but fertilizer placement did. The study was conducted by University of Manitoba soil scientist Mario Tenuta and funded by Manitoba Canola Growers, SaskCanola and Koch Agronomic Services. The paper correctly reasons that western Canadian canola growers are shifting toward surface application of granular urea for three reasons.

  • Pressure to complete field operations
  • Increased use of custom applicators
  • Cheap nitrogen

This shift is a departure from the recommended practice of deep banding, which significantly reduces nitrogen loss through ammonia, NH3, volatilization. Deep banding remains the recommended method with respect to protecting nitrogen fertilizer from gaseous losses through NH3 volatilization or N2O emissions.

However, the study concedes that deep banding requires more horsepower and slows field operations in fall or spring. Plus, it may have a negative impact on seedbed quality and moisture content.

Manitoba Agriculture fertility specialist John Heard says, “Fall broadcast is 20 percent less efficient than fall-banded or spring broadcast and 40 percent less efficient than spring-banded fertilizer. These banding recommendations have been around forever. Dr. Al Ridley at University of Manitoba developed them in the 1980s. It’s like Moses carried them down from the mountain on the tablets.”

Heard says the spreader trend is spreading. He says we cannot ignore the number of new innovative spreaders coming to the market. The message is clear: farmers are turning back the hands of time on precision agriculture.

Heard poses the question, “How can we apply the term precision to a machine that leaves fertilizer on the surface instead of precisely placing it into the soil at a recommended depth?”

As a compromise, notes Heard, some growers shallow-band urea at a depth of about one inch. Many of the producers who surface apply tend to use commercially available enhanced efficiency fertilizers to reduce NH3 losses, such as SuperU or Agrotain,

In his research Tenuta compared the agronomic and environmental performance of surface-broadcast, shallow-banding and deep-banding methods to reduce nitrogen loss and maximize yield. Six research trial sites were run from 2014–16 in the Red River Valley to evaluate the agronomic and environmental performance of source urea, Agrotain and SuperU. The comparisons included fall broadcast, fall shallow, fall deep, spring broadcast, spring shallow and spring deep

All trials were conducted with 100 percent of the Manitoba Agriculture recommended rates. The inclusion of a 70 percent rate in the experiment was to provide less nitrogen than needed by the canola crop to highlight treatments providing better nitrogen efficiency. N2O emissions were documented from urea, SuperU and ammonia volatilization.

In an email interview, Tenuta says, “I should mention that the fall-broadcast treatments were not something originally in the project proposal to the canola growers. A fertilizer company wanted them in there to show benefit of their product.

“It didn’t work. Yield was very much lower with surface-fall applications regardless of whether or not inhibitors were included.”

Go deep or go home — the results of the study indicate the nitrogen source did not affect canola yield, but fertilizer placement did.

Spring-surface applications showed yield losses from three to five bu. per acre compared to shallow or deep banding.

Fall-surface applications of granular urea and enhanced efficiency products with urease and nitrification inhibitor showed a 13 bu. per acre yield reduction compared to spring-surface applications of the same products. That pencils out to an 18 bu. yield reduction for fall broadcast compared to banding.

Across the full study, NH3 volatilization was generally low. However, there was a clear trend of less loss with surface-placed SuperU when compared to surface-placed urea. There were lower losses with the sub-surface banding compared to surface-urea treatments. Similarly, N2O emissions were lower with SuperU than they were for urea, and lower with subsurface banding than with surface placement.

These results verify past research that subsurface banding of granular urea improves yields compared to surface application. As well, fall surface applications are less efficient than spring applications.

The study does not take into account the fact that many pounds of nitrogen are lost.

It may have been relatively cheap this year. But it is lost.

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