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Establishing safe seed-placed ESN rates

As a polymer-coated, “slow release” urea fertilizer, Environmentally Smart Nitrogen (ESN) urea has a fit for single-shoot seeders or other seed-placed configurations, as it has been proven the ESN urea reduces seedling toxicity by slowing the release and conversion of urea to ammonia.


March 17, 2010
By Bruce Barker

As a polymer-coated, “slow release” urea fertilizer, Environmentally Smart Nitrogen (ESN) urea has a fit for single-shoot seeders or other seed-placed configurations, as it has been proven the ESN urea reduces seedling toxicity by slowing the release and conversion of urea to ammonia.

esn_fertilizer
Research is looking to find the upper limits of safe seed-placed ESN fertilizer: 90 lbs of ESN per acre was too high for canola, as was 60 lbs of uncoated urea per acre. (Photos by Bruce Barker)


“The question remains, what are the upper limits of safe seed-placed ESN-coated urea?” asks researcher Brian Beres at Agriculture and Agri-Food Canada (AAFC), Lethbridge, Alberta. 

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Agrium, the manufacturer of ESN urea, has set its safe recommendation for seed-placed ESN at a rate that can exceed uncoated rates by up to 50 percent. Beres says that the recommendation may be conservative, and that it is likely many farmers routinely exceed that guideline.

Work by Ross McKenzie with Alberta Agriculture and Rural Development (AARD) on several ESN prototypes started to establish the upper limits. In his trials on winter cereals, stand densities were substantially reduced by seed row application of uncoated urea at rates greater than 30 kg of N per hectare (27 lbs of N per acre), but were unaffected by seedrow application of ESN urea at 120 kg of N per hectare (107 lbs of N per acre). “In this case, we could probably state that it is safe with a three times rate of urea when seed-placed ESN was used in winter wheat,” says Beres. He cautions, though, that the integrity of the polymer coating was probably pristine in this trial, as the ESN prototypes were handled carefully, and seeding was with a gravity-fed plot drill. “Any abrasion to the polymer coating could result in faster conversion of urea to ammonia and increased seedling toxicity.”

Assessing abrasion effects
To test the impact of abrasion on ESN urea, Beres worked with Agrium in an abrasion and water release study to help determine the impact of retail and on-farm handling on ESN abrasion, and, ultimately, the safety when seed-placed with canola or winter cereals. The first step was to develop in-field crop response thresholds for physically altered ESN. Agrium supplied Beres with nine samples that ranged from unabraded to 80 percent N release rate as measured by the amount of N released after immersion in 23 degrees C water for seven days. The N release rate reflects the amount of damage to the polymer coating with higher release rates resulting from higher damage to the polycoat. He measured stand establishment, vigour, leaf area index and normalized difference vegetation index (NDVI) in winter cereals and canola. 

At a seed-placed ESN rate of three times the safe rate of uncoated urea, detrimental effects as a result of abrasion started to occur in the range of 40 percent water N release for canola and 60 percent water N release for winter cereals. The ESN rate was 90 kg of N per hectare (80 lbs of N per acre) for winter cereals and 45 kg of N per hectare (40 lbs per acre) for canola.

With that knowledge in hand, Beres looked at how retailer and on-farm handling damaged the ESN coating, and correlated it back to crop damage. He looked at abrasion when loading ESN through a blender at the retailer, using a drill fill on the farm, and in nine different application implements. “When good handling and quality assurance are practiced, you can expect to see a 20 to 30 percent release rate from the ESN. We didn’t see any negative effects on crop parameters at this rate,” says Beres.

The most serious abrasion was seen under several different scenarios. The first was seen when transferring ESN through equipment with scaly deposits, which Beres calls “dirty” ESN. For example, scale can build up in a blender and damage ESN, but if 10 tonnes of potash were run through the blender prior to running ESN through it, the potash would polish the augers and reduce abrasion. A drill fill also was found to cause some abrasion, but the effect was moderate compared to the scaly blender at the retailer. 

The Flexi-Coil Easy Flow air manifold also raised a red flag when combined with ESN loaded with a scaly blender.  “Air drills configured with this style of air or product delivery have a higher degree of deflection at the manifold, which is why we observed increased abrasion with this air drill compared to the other drills that do not have header-manifold style systems.” 

“We started to see some concern when dirty ESN was run through the Flexi-Coil header manifold, with release rates of more than 60 percent. That started to have an impact on crop establishment,” explains Beres. “But, if clean ESN was used the negative impact was minimized significantly. Therefore, it is critical for retailers to ensure clean loading equipment is used to handle ESN, and producers should always check that wind speeds in air drills are calibrated properly.”

Beres says the results of all the trials to date point to safe ESN rates of 45 kg of N per hectare (40 lbs of N per acre) for canola and 90 kg of N per hectare (80 lbs of N per acre) for winter cereals. He says that further study is required to establish safe upper limits for seed-placed ESN in both ideal and less favourable conditions. “These results are based on proper handling of the product. If you suspect that there is abrasion, you would want to back off on those rates,” explains Beres.