What fertilizer practices are the worst for losses?

For this article, we asked fertilizer specialists to describe significant nutrient-loss scenarios that consider loss risks based on product, timing, placement, soil conditions and weather. “The purpose of the article,” Canola Digest explained when asking for their input, “is to identify high-loss situations and provide better options, using 4R thinking and perhaps enhanced-efficiency tools to benefit farm profitability and the environment.” Here are their responses, in their own words.

Don Flaten (with Mario Tenuta)
University of Manitoba

“The biggest nutrient-loss scenario in Manitoba is broadcasting nitrogen (N) fertilizer in the fall. ”

—Don Flaten and Mario Tenuta

The biggest nutrient-loss scenario in Manitoba is broadcasting nitrogen (N) fertilizer in the fall.

Fall broadcasting of N fertilizer seems to be increasingly popular in some areas of the Prairies, probably due to the cheaper cost of fertilizer in the fall vs. spring, as well as being faster and cheaper, compared to subsurface banding. However, fall broadcast N is vulnerable to losses that decrease its agronomic efficiency and increase its risk of environmental problems.

According to the Manitoba Soil Fertility Guide, fall broadcast fertilizer averages 40 per cent less efficiency compared to banding in the spring. This issue of poor efficiency of fall broadcast N is even worse if the soils are waterlogged in early spring.

Therefore, if N fertilizer is applied in fall, it should be banded, preferably as late as possible, especially for low-lying areas of fields that might be ponded with water during snowmelt. That’s because banding helps to slow down the conversion of N fertilizers such as urea (46-0-0) or anhydrous ammonia (82-0-0) into nitrate, which is vulnerable to leaching and denitrification. Furthermore, banding also helps to reduce volatilization and the amount of N immobilized by soil microbes.

John Heard, crop fertility specialist with Manitoba Agriculture, adds: The temptation to fall broadcast nutrients (as fertilizer P and N or manure) onto frozen soil may have helped prompt development of our Manitoba regulations prohibiting winter applications.

Jeff Schoenau
University of Saskatchewan

“One other thing that comes to mind for drier environments like southern Saskatchewan is related to anhydrous ammonia and the potential for significant volatilization losses (escape of ammonia) if shallow application is made in dry sandy or lumpy soils.”

—Jeff Schoenau

The nutrient loss scenario of surface broadcast of granular fertilizer, as covered by Don and Mario, certainly pertains to Saskatchewan as well. One other thing that comes to mind for drier environments like southern Saskatchewan is related to anhydrous ammonia and the potential for significant volatilization losses (escape of ammonia) if shallow application is made in dry sandy or lumpy soils.

Injected ammonia is retained in the soil by reacting with mainly with water and other proton donors like organic matter and clay mineral surfaces. This converts the ammonia gas to the ammonium ions that are retained in the soil. If the surface soil is very dry and sandy, one should place the ammonia deeper to moisture to aid in retention and conversion to ammonium. The greater depth also gives the ammonia gas more opportunity to react with water and the soil before it diffuses through the pores to the surface. Also make sure the injection channel is closed up well behind the opener.
If the soil is very lumpy with large pores, this will reduce contact and increase rate of movement of ammonia gas to the surface. Under these conditions, a granular or liquid form of N may be a better selection, but even with these forms it is important that the fertilizer is covered with soil to retain the ammonia gas that is produced by hydrolysis of the urea.

To demonstrate this to my students, I use a classic study by Stanley and Smith (Soil Sci Soc Am J., 1956). With anhydrous ammonia applied at 100 pounds of N per acre to a silt loam soil, the study found losses of ammonia in excess of 10 per cent from three-inch depth in a silt loam when soil moisture was very dry (only three to four per cent moisture), but when soil was moist (18 to 20 per cent moisture), losses dropped to less than one per cent. Ammonia losses were reduced in the dry soil conditions when depth of application was increased.

For granular urea or UAN, a urease inhibitor would help reduce potential volatile ammonia losses from shallow banding. I think especially under conditions of high loss potential – sandy, dry, high pH – that there can be economic benefit from the inhibitor. However, there is no product additive for anhydrous ammonia to stop volatilization. Paying attention to depth and sealing of band is important for all ammonia containing and producing fertilizers.

Mario Tenuta in Manitoba adds to the anhydrous ammonia conversation: The best management practice for anhydrous ammonia is deep injection under moist conditions with good slot closure and band coverage, and ideally into cool soil temperatures.

Len Kryzanowski
Alberta Agriculture and Forestry

Between 2007 and 2012, we conducted a province-wide research study comparing ESN, urea and a blend (75 per cent ESN and 25 per cent urea) under a range of application options and conditions to assess the agronomic, economic and environmental performance of the treatments and to provide recommendations about when to use which option. The study had nine sites from north to south, including one irrigated.

Results showed that agronomically, spring application tended to be better than fall, with higher yields and greater nitrogen use. As expected, seed-placed urea resulted in the poorest growth and greatest seedling damage. In comparison, the seed-placed blend (ESN and urea) allowed higher nitrogen rates without seedling injury, and the seed-placed ESN allowed even higher rates.

If you want to use urea, then banding is a much better option. If you want to seed-place your nitrogen fertilizer, then ESN or ESN-urea blend is the best choice because it results in less seedling damage, more yield and greater productivity.

To evaluate the economics, we examined whether the value of the crop’s additional yield with ESN or the blend was large enough to offset the higher fertilizer costs compared to urea, using a partial budget approach. This analysis helps growers decide whether they should pay the extra for ESN rather than use urea alone. When nitrogen is seed-placed with canola, the blend would have the best chance of being worth the extra cost. And seed-placed ESN would have a good chance of being worth the extra cost, at most sites, when canola prices are high.

The greatest economic benefits from using ESN or the blend were for canola, followed by wheat and then barley. For all three crops, the economic results varied greatly within sites, between sites and between years due to regional differences. Some sites were highly economical, such as under irrigation where it was easy to get higher yield productivity using ESN or the blend. But in drier conditions the results became much more variable.

“Typically there was between 17 and 25 per cent reduction in nitrous oxide emissions by going from fall-applied to spring-applied nitrogen. Spring application avoids that most critical time for nitrogen loss – the thawing period.”

—Len Kryzanowski

The study also measured nitrous oxide emissions. Spring application was clearly the most effective way to reduce emissions. Typically there was between 17 and 25 per cent reduction in nitrous oxide emissions by going from fall-applied to spring-applied nitrogen. Spring application avoids that most critical time for nitrogen loss – the thawing period. ESN resulted in somewhat lower emissions than urea. Switching from fall-applied urea to fall-applied ESN resulted in about a six per cent reduction in emissions. (See the table for results.)

In closing, I will add, from the Alberta perspective, that I also agree with the comments on fall broadcast application of nitrogen fertilizer as noted at the beginning by Don and Mario.