Your Reading List

Slow Release N A Good Fit In Wet Areas

Does slow release nitrogen make a difference? That was the focus of a recently completed, four-year study by Agriculture and Agri-Food Canada, which looked at canola and barley response to ESN and urea in a no-till system.

ESN (Environmentally Smart Nitrogen), developed by Agrium Inc., is a polymer-coated, granular urea fertilizer, which slowly releases nitrogen (N) into the soil. Part of the premise behind the product is that gradual release of N better meets the fertilizer needs of the crop throughout its growth cycle and also prevents N loss into the atmosphere or deeper soil layers.

“If you have a large amount of N that is released very quickly into the soil, at the beginning stages of the crop, it can’t utilize it all,” explains Dr. Robert Blackshaw, lead researcher for the study.

“Hopefully, most of that N will remain in the soil for later in the growing season. But if the soil is very wet you can have a loss of N into the atmosphere, and with heavy rainfall you can have some leaching of N into the lower layers of the soil and it can be lost permanently.”

There were several aspects to the study, which involved three Alberta test sites (Lethbridge, Lacombe and Beaverlodge) and two in Saskatchewan (Scott and Melfort). Yields were compared between the ESN and urea fertilizer treatments, which were applied at a 100 per cent and 150 per cent of the recommended soil test rate. Both canola and barley were grown at each site each year, yielding 20 “siteyears” of data. The canola cultivars grown were a hybrid type and an open pollinated (OP) type. Barley varieties used in the study were semi-dwarf and tall cultivars. Registered herbicides were applied at 100 per cent and 50 per cent rates to both crops.


A big assumption at the beginning of the study, says Blackshaw, was that the existing recommendations for N fertilizer rates for hybrid canola cultivars might not be high enough to achieve maximum yield potential.

“There was a suspicion that hybrid canola could probably use more nitrogen,” says Blackshaw.

But the assumption proved false. The researchers used both a 100 per cent and a 150 per cent fertilizer rate, but found little difference between cultivars in the yield response to increased N. Both the hybrid and OP canola cultivars expressed a positive yield response to the 150 per cent N fertilizer rate in 10 of 20 siteyears. In only three of the 20 site-years did the yield of the hybrid variety respond to the additional fertilizer when the OP variety did not.

There was also no significant cultivar difference in yield response to the ESN and urea treatments. Canola yields were similar with ESN and urea in 14 of 20 site-years.

“About 25 per cent of the time, ESN gave an advantage in terms of canola yield,” says Blackshaw.

There are some situations, however, particularly during wetter than average conditions, where ESN does appear to provide additional advantages over urea. In a related experiment that was conducted at Lethbridge this past spring, Blackshaw and his team noted that canola crops planted late in the season, because of extremely wet conditions in May and early June, were responding differently to ESN and urea treatments.

“We could see that with the ESN treatment, the plants in July were a darker green colour than the plants that had received the urea treatment, which meant they had taken up more nitrogen,” says Blackshaw. “So probably some of the urea was lost, but more of the N was remaining in the ESN treatment.”

Results were similar for the barley sites, with once again a yield increase being seen in about 25 per cent of the sites that were treated with ESN.

So it would appear that ESN may have definite advantages in some situations where there is a greater potential for N losses, such as in areas with very porous or poorly drained soils or in very wet years.


Of course, N that is available to the crop is also available to the weeds, so researchers were anxious to find out if there was any advantage in using ESN to slow down N uptake and reduce weed competition with the crop.

Results seemed to indicate that this may be the case, particularly in the hybrid canola variety, where weed tissue N concentration was reduced in 70 per cent of the cases (compared to the OP variety) when ESN was used.

Although the results were not quite as dramatic in the case of the barley crops, there is strong evidence that crop-weed competition for soil N may be reduced when ESN is used instead of urea.

Overall, weed biomass did not seem to be affected by the type of fertilizer used or the rate of fertilization, although in a few cases the 150 per cent rate did result in more weed biomass, which illustrates the importance of a good weed management program when using higher fertilizer rates.

As might be expected, weed biomass in both barley and canola was greater in almost all of the sites using the 50 per cent herbicide rate than in those using the 100 per cent rate. Interestingly, there was no significant difference in the amount of weed biomass between the OP and hybrid canola varieties, which did not support previous research findings, where herbicide rates could often be reduced in hybrid canola because it was more competitive with weeds.


Although there was very little difference in the oil content for any of the canola sites, the study found barley from fields treated with ESN had higher protein content about 40 per cent of the time. This is statistically significant, says Blackshaw. A higher protein level is generally

desirable when it comes to cereal crops, such as wheat and feed barley, because it offers more nutritional value.

Blackshaw’s theory is that during the first two-thirds of its growth stage, a plant is using any available N to generate yield potential. Once it reaches the final stage of heading or seed development, there is often little N left available in the soil with a regular urea fertilizer.

“But in a system where you use ESN you have some N still being released later on in the growing season,” says

Blackshaw. “So there is a little bit more N available to move into the seed and that gives you higher protein content.”

The study also measured greenhouse gas emissions and found that, all things being equal, nitrous oxide emissions were sometimes lower with ESN than with urea. During wet conditions, however, the effect was amplified and ESN further reduced the amount of nitrous oxide going into the atmosphere.


New technologies often cost more than traditional systems and ESN is more expensive than straight urea, so the economic case for using it will come down, as it often does, to the unique requirements of each farm.

“Depending on the price differential between ESN and urea, farmers might want to think about where would be the best situation to use it,” says Blackshaw. “There are some situations where the use of ESN could be positive and it could be beneficial in terms of the environment and yield and quality.”

This comprehensive study of the various comparative responses to ESN and urea should provide a useful foundation upon which to build more cost-efficient and environmentally sound fertilization programs for field crops, says Blackshaw.



It would appear that ESN may have definite advantages in some situations where there is a greater potential for N losses, such as in areas with very porous or poorly drained soils or in very wet years

About the author


Angela Lovell

Angela Lovell is a freelance writer based in Manitou, Manitoba. Visit her website at or follow her on Twitter @angelalovell10.



Stories from our other publications