The federal government has set a national target to reduce absolute levels of greenhouse gas emissions arising from fertilizer applications by 30 percent below 2020 levels by 2030.
In December 2020, Canada announced its Strengthened Climate Plan, “A Healthy Environment and a Healthy Economy.” This paper listed a number of industries including agriculture that were the largest emitters of GHG in Canada.
For perspective, the agriculture industry accounted for about 73 megatonnes (Mt) carbon dioxide equivalent or 10 percent of Canada’s total emissions. That ranks our industry fifth among the big emitters. We are right behind buildings and heavy industry.
According to Canada’s National Inventory Report for 2019, the 73 Mt carbon dioxide comes from three main sources: enteric fermentation (33 percent), crop production (33 percent), and on-farm fuel use (19 percent).
I’m going to mainly discuss the 33 percent, or about 3.3 percent of Canada’s total emissions, that comes from crop production. A little over half of this number comes from emissions that result from fertilizer and specifically nitrogen fertilizer applications.
When the Healthy Environment document was released, there were a number of articles and farm groups reacting to the goal to obtain a 30 percent reduction in on-farm emissions from 2020 levels of nitrogen fertilizers by 2030. Virtually all the GHG emissions resulting from nitrogen fertilizer applications occur as nitrous oxide, a potent greenhouse gas with a global warming potential 265 to 298 times that of carbon dioxide during a 100-year period.
I am going to focus on the processes that convert fertilizer nitrogen to nitrous oxide and then go over some of the management practices that can reduce those emissions.
The nitrogen cycle is complicated compared to other nutrient cycles, as well as the carbon cycle and water cycle. As well, it is leaky with a number of pathways for nitrogen to leave.
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For example, N can volatilize from soils as ammonia, which can be harmful for biodiversity and travel extensive distances and react with particulate matter to cause smog. The N volatilized is redeposited in the environment where a fraction of it converts to nitrous oxide. The largest contributor to volatilization losses is broadcast applications of urea.
Volatilization losses are a minor and indirect contributor to nitrous oxide emissions. Two soil processes, nitrification and denitrification, result in direct emissions of nitrous oxide and together account for most of the emissions attributable to fertilizer nitrogen.
Soil micro-organisms convert nitrate-nitrogen to gases such as nitric oxide, nitrous oxide and finally dinitrogen, which are lost to the atmosphere. This is denitrification.
Considerable nitrate-nitrogen may be lost by denitrification when soils are warm and saturated (after heavy June rainfall) or during spring flooding.
Under saturated conditions, the excess moisture fills air pockets in the soil. Micro-organisms run out of oxygen and start using up the oxygen in nitrates instead, leading to denitrification.
Nitrification, the microbial conversion of ammonium to nitrite and then nitrate, is the other soil process resulting in significant direct nitrous oxide emissions.
Generally, the faster ammonium is converted to nitrate the more nitrogen is shunted off as nitrous oxide. Leaching and runoff of nitrate can, like volatilization, result in indirect emissions if denitrification of lost nitrogen occurs outside the cropping system.
In general order of importance, denitrification, nitrification, leaching and volatilization are the processes that lead to nitrous oxide emissions. The challenge that the government is setting out is to reduce these emissions by 30 percent by 2030. The challenge for the industry is to reduce these emissions by 30 percent without reducing yields or profitability.
There has been extensive research carried out for the past 20 years that says that it probably can be done – but it won’t be easy. The good news is if we can prevent losing nitrogen, it becomes a win-win.
We have reduced emissions into the atmosphere but we have also saved that nitrogen for the crop to use. At $1.20 a pound for nitrogen, this will be economically significant.
So how do we go about reducing these nitrous oxide emissions? You have likely heard of the 4R Nutrient Stewardship program (right source at right rate, right time, right place) promoted by Fertilizer Canada, governments and other agencies.
Following the 4R best management practices with regards to nitrogen will take us a long way to achieving a 30 percent reduction in GHG emissions.
Agriculture Canada has created a discussion document titled Reducing Emissions Arising from the Application of Fertilizer in Canada’s Agriculture Sector. It reviews the areas that organization sees as targets for the reduction of GHG emissions in agriculture. The following table is from that paper and summarizes areas they see as targets for reducing nitrous oxide emissions.
These are not the only best management practices (BMPs) that can reduce nitrous oxide emissions but I would like to give you my perspective on these targets because they are the ones covered in the discussion paper and the only nitrogen management practices that Ag Canada is supporting through the On-Farm Climate Action Fund.
The report follows the 4Rs for categorizing most of its BMPs. Under right rate, they target testing soils yearly for nitrogen inventories. This can then be used to determine an inventory of soil nitrogen. This practice, however, has to be coupled with an accurate yield target and the two numbers then used to derive appropriate application rate. Since the early 1960s, this has been the goal of successive extension programs, to get more fields soil tested.
We have recently seen a rapid uptake of soil sampling. Most of this can be explained by the adoption of variable rate technology (VRT).
This leads me into a big omission in the right rate category. The adoption of VRT accomplishes two goals. Firstly, VRT fertility applications requires annual soil testing, not only for a field but for individual zones or sub-fields within that field. Secondly, once the right rate is established for a zone, the right rate is applied to that zone. This eliminates over application of nitrogen, which leads to increased nitrous oxide emissions. It also improves the nitrogen-use efficiency (NUE). NUE is generally defined as the amount of N taken up by the crop per unit of nitrogen applied. As there appears to be a direct correlation between the amount of N-based fertilizer and nitrous oxide emissions, I would postulate that by increasing NUE, we would see a reduction in nitrous oxide emissions.
The second discussion point under right rate category is accounting for N in previous legume crop. The current adoption level is indicated as medium to high.
From my experience working with pulse crops and small grains, the adoption rate is high. Most growers will modify the crop grown and the nitrogen rate applied based on the nitrogen credit from the previous crop. This also goes for farmers who terminate perennial legume crops like alfalfa.
Looking at the right time segment of the 4Rs, the report identifies the application of N in the spring as a major target. They indicate this as having a high adoption level. I agree with this, in some years, but suggest it may be difficult to accomplish without major infrastructure improvements into fertilizer distribution.
The fertilizer industry is built on the assumption that in any given year, 20 percent of the nitrogen fertilizer may be applied in the fall. The vast majority of fall-applied fertilizer is applied as anhydrous ammonia (NH3). The facts are that current containment facilities, bulk anhydrous ammonia storage tanks and field delivery and application equipment are only capable of handling two-thirds of current requirements in a single season (fall or spring).
Secondly, nitrogen fertilizers are usually cheaper in the fall compared to the following spring. Up until four or five years ago, I observed that in nine out of 10 years, the price of urea or NH3 in the fall is about 85 percent of the spring price. The fall-spring price discrepancy has only widened over the last two seasons.
Finally, farmers in much of Western Canada know the benefits of applying fall nitrogen. The time management aspect is key for growers being able to seed early without the necessity of pre-banding their nitrogen in the spring.
Fall applied N can be effective and cost effective. It also works well into time management when fall conditions allow.
The risks of overwinter nitrogen losses are real, but there are management practices that will lower these losses. These include:
- Avoid using products that contain nitrate — N such as UAN (28-0-0 or 32-0-0).
- Wait until the soil has cooled below 10 C before beginning applications.
- Target for a banding depth of at least 7.5 centimetres deep with less than 10 percent overall soil disturbance.
- Ensure proper soil closure behind NH3 shanks.
- Avoid poorly drained fields or portions of fields where water is prone to lie in the spring.
By following these BMPs, nitrification will be slowed, less nitrate will accumulate, and the potential for denitrification will also be reduced.
The use of nitrification inhibitors or coated urea will allow you to cheat a little on the above practices and still reduce nitrous oxide emissions with fall applied N.
Fertigation (injection of fertilizers with irrigation) has been targeted as an option to applying nitrogen fertilizers and reduce nitrous oxide emissions.
When compared with applying all nitrogen at planting, the application through irrigation water will reduce nitrous oxide emissions when the period between planting and first irrigation is excessively wet, causing saturated soil conditions.
Split application/side-dress with rate adjustment based on sensors has been shown to be an effective method of reducing over-application of nitrogen. Sensors like the Green Seeker offer a real-time measure of crop nitrogen deficiencies and allow for corresponding rate adjustments in those areas where deficiencies are indicated. This technology probably only applies to corn and to areas where side-dressing is practiced.
In the future, as equipment becomes available, western Canadian growers may be able to use this practice.
They also can use NDVI imagery from satellites to develop application prescriptions. Recent developments of sophisticated algorithms tied into soil and weather sensors have also proven effective in predicting in-field nitrogen levels and alerting growers to apply nitrogen in-crop. An overhanging issue with split applications in Western Canada is the shortness of the target application window and one rain may cause the window to be missed, resulting in yield loss due to insufficient nitrogen.
The right place is the next of the 4R categories. This can be summarized by stating that nitrous oxide emissions are reduced and NUE improved any time you band or inject nitrogen fertilizer into the ground.
Research going back to the 1980s shows this improvement. This has been illustrated with fall or spring banding of urea or anhydrous ammonia, in side-banding at seeding and with mid-row banding of these two products as well as UAN.
This improved performance is also seen when side-dressing is compared to surface banding as a top-dress application.
The fourth and last of the 4Rs is right source — choosing the right nitrogen fertilizer for your situation.
The selection of nitrogen-based products like urea, anhydrous ammonia, UAN or ammonium sulphate, when using BMPs as described above, using the right rate, timing and place can be used as effective fertilizer N sources with reduced risk of nitrous oxide emissions.
In addition to the traditional nitrogen sources, there has been myriad of efficiency fertilizers, inhibitors and slow-release products introduced into the market in recent years.
Many of these products will inhibit or reduce the conversion of ammonium to nitrate (nitrification). Broadly speaking, they are all referred to as nitrification inhibitors. Products like nitrapyrin (found in N-Serve and eNtrench) act as a bactericide that kills nitrosomonas bacteria. It has been around for years, but only recently has it become widely used.
Other products such as dicyandiamide (DCD) and pronitridine inhibit the growth of this class of bacteria. Meta-analysis has shown that nitrification inhibitors typically reduce nitrous oxide emissions from 20 to 40 percent.
A second group of chemicals are called urease inhibitors. The most commonly used urease inhibitor is N-butyl-thiophosphoric triamide (NBPT). These products are used with urea or UAN to slow the conversion of urea to ammonium and reduce volatilization losses from surface applied or shallow-banded products. While urease inhibitors are effective at preventing volatilization loss, they are far less effective than nitrification inhibitors at reducing nitrous oxide emissions.
Often a nitrification inhibitor will be combined with a urease inhibitor to reduce volatilization, slow nitrification and nitrate accumulation and reduce the risk of denitrification losses.
Other products that have been developed for use with urea are coatings that act to produce a controlled-release product.
The most popular of these products is ESN, which uses a polymer to coat the urea and regulate the nitrogen release. Polyon and Duration are other examples of polymer coatings for urea.
Some products will use a coating in combination with a urease or nitrification inhibitor for additional protection.
Get comfortable with these types of products because they will become a larger component of nitrogen applications.
The biggest drawback is the cost, with an increase of 10 to 20 percent compared to bare urea or ammonia commonly being charged.
Hopefully, this is one area where government incentives can be used to lower the difference. The good side of these products is that, when conditions favour losses, they can result in higher yields at the end of the year.
The other topic listed under right source is the replace inorganic fertilizer with manures, compost, or digestate. While a noble goal, the fact is, as far as I am aware, the use of manures is very high relative to availability.
This is contrary to the adoption column, which is listed as low. My observations come from hog, chicken, turkey and cattle operations in eastern Saskatchewan and northwestern Manitoba. However, I am also aware that in all three provinces, any larger livestock operation must have a manure management plan in place. This will include the disposal of manures in a sustainable manner. There may be opportunities to improve the efficiency and GHG reductions based on application methods. Composting materials is not really a method of reducing GHGs as carbon dioxide, methane and nitrous oxide are all released at significant levels during the composting process.
With recent announcements the federal government seems committed to providing financial incentives to farmers to reach its 30 percent reduction in GHG emissions.
The biggest response I’ve heard from growers is that western Canadian farmers have been sequestering carbon for the past 25 years and should be compensated.
Correct. However, the fact is that we are only now approaching a net-zero point where the GHG emissions from N20 and burning fossil fuel is equalling the C02 sequestered in our soils.
The fact is if you aren’t a part of the solution, you are part of the problem. If you are using tillage as a management practice; if you are not following the management practices outlined in the 4R Nutrient Stewardship strategies, you are probably part of the problem.
Expect government incentives to reduce GHG emissions but also expect restrictions on some of your agronomic practices and products.
I would ask you to take a few minutes and read the document: Reducing emissions arising from the application of fertilizer in Canada’s agriculture sector — Agriculture Canada — 2022-03-30 and think about how what is discussed in the document relates to your farm.
Take an inventory of your practices and challenge yourself to come up with strategies that may reduce GHG emissions by 10 or 20 percent on your farm.
In my next article, I will discuss carbon sequestration and the role conservation tillage plays in the whole GHG emission picture.
Thom Weir PAg is a certified crop advisor and professional agrologist in the Yorkton, Sask., region. You can reach him at thom.weir@farmersedge.ca.
