Nitrogen is a critical nutrient, essential to life and agriculture, but its byproduct, nitrous oxide (N₂O), is also a powerful greenhouse gas, emissions of which the federal government has aimed to slash.

Canadian agriculture is now several years into the federal goal to reduce N fertilizer emissions by 30 per cent below 2020 levels by the end of the decade. Similar regulations have caused tension in the European Union and elsewhere.

Kate Congreves, a University of Saskatchewan associate professor, has been researching how to improve crop production while limiting nitrogen emissions as part of the second Diverse Field Crops Cluster (DFCC). The most recent five-year cluster started in 2024.

Preliminary results keyed in on the mix of different application techniques and products that resulted in more efficient nitrogen management.

READ MORE: Rethinking nitrogen efficiency

“Nitrogen fertilizers are the largest source of anthropogenic N₂O emissions,” she said during a March presentation.

“What this means (is), if fertilizers and fertilizer applications are a large source of N₂O emissions, anthropogenic N₂O emissions, that means our adjustments to fertilizer and fertilizer management do have an impact on reducing emissions.”

DFCC focuses on research on diverse crops such as camelina, carinata, flax, sunflower and mustard. Spring wheat is tapped as a control.

One of her hopes is to identify “double wins” — that is, the high-value crops associated with the lowest emissions.

Win-wins

The project builds on nitrogen emission test results and practices established in Nitrous Oxide Emission Reduction Protocol (NERP), created in collaboration with Fertilizer Canada. NERP forms a set of guidelines, with a goal of helping the producer hone their N management, reduce emissions, but also protect their crop production.

There are three levels for NERP: basic, intermediate and advanced. “Basic” uses ammonium-based fertilizer applied at seeding, with a rate established from soil testing information. “Intermediate” expands management to include options such as enhanced-efficiency fertilizers, applied at a reduced rate (around 75 per cent of the basic rate), since less would be presumably needed for the same crop effect. “Advanced” NERP guidelines use enhanced-efficiency fertilizer as well, but applied with split application between seeding and in-season.

These guidelines are followed closely in the DFCC project. Congreves uses SuperU at the intermediate level as the enhanced efficiency product, and SuperU with split application at the advanced level. Intermediate treatments band at 75 per cent rates of the basic treatments, and advanced bands at 75 per cent of intermediate (totalled between applications), the first of which occurs at seeding and the second at crop emergence. The in-season application was done with backpack sprayers to ensure uniformity of application.

The project has three research sites in Saskatchewan. Each site is on clay loam soil with similar levels of organic matter and pH. Background soil N, however, is varied. The sites are categorized as having low, moderate or high existing nitrogen levels.

“The background nitrogen levels, they do have an influence on nitrogen cycling,” Congreves says. “And soil priming affects how much nitrogen that would subsequently get released from soil organic matter, for example, and then you’ve got nitrogen from the fertilizer.”

These background levels were one of the factors that went into determining the plots’ treatment levels. Others were consultation of crop fertilizer guidelines, reviews of estimates for soil mineralized land potential during the growing season, and NERP guidelines.

Sampling

Seeding across all sites was underway in mid- to late May 2024. Bases that would allow the team to measure emissions were installed immediately following seeding and fertilizer passes, placed in every plot, maintained throughout the season and sealed at the surface of the soil. Chambers were attached to the top of the bases to capture gases to be measured.

Samples were taken several times a week, but more frequently right after seeding and rainfall events, as these periods see the most flux (the rate that greenhouse gases are added or removed from the air).

“We go in and seal the chamber air tight and we collect our gas samples… with a syringe,” Congreves says.

Samples are taken at various points after the chamber is sealed. To measure the sample, the team uses gas chromatography, a technique that separates organic or inorganic substances from a gas to be analyzed, so as to see the N₂O concentrations in the emitted gas.

Findings are paired with data kept on soil moisture, temperature, weather condtions and crop production, as well as information from soil and plant samples.

Looking at the results from mustard, Congreves notes that, at the side with moderate levels of background nitrogen, there were incremental “additive” amounts of N₂O throughout the growing season.

“What we’re seeing is N₂O emissions are indeed greater with basic, and then incrementally lower with intermediate, advanced, and then our unfertilized control,” she says.

The site with high background N levels saw larger daily fluxes at application time, but not as many during the growing season. Following this pattern, the site with the lowest background levels had the lowest major emissions.

Congreves says she’s not yet seen any major yield differences associated with the practices. Her 2024 yields had normal rates of variability that were on par with other small plot agronomy trials and aligned with 2024 crop averages.

The other crop data sets show similar patterns.

However, the reasearch is far from wrapped. Spring thaw is a major point of emissions. When the spring 2025 emissions are measured, the cumulative emissions will be adjusted to officially cap off the first year of the project.

“So far we’re indeed seeing, for most crops, the same pattern… so far, based on 2024 preliminary data, improving the nitrogen management practice does tend to practically reduce (cumulative) N₂O emissions.”

Going forward, Congreves notes they plan to link N use efficiency metrics to N₂O data to get a “fuller picture” of what occurs with the gasses and the crops together.

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The nitrogen-fixing family of plants, Leguminosae, number in the tens of thousands. These nitrogen-fixing legumes range in size from tiny clovers to shrubs like caragana and to full-sized trees. Our agriculturally well-known legume crops range from peas and beans to alfalfa, peanuts and soybeans.

Nitrogen is also fixed on the prairies by free-living bacteria, fungi and different bacteria in association with common shrubs and trees like wolf willow and alder. And, you may be surprised to learn that about 15 per cent of the world supply of nitrogen comes from lightning storms in the form of nitrates.

The Haber process for manufacturing nitrogen is a sort of modified lightning storm, combining nitrogen with hydrogen to produce ammonia. The industrially fixed bagged nitrogen is no different from the five to 15 pounds of fixed nitrogen that falls on cropland per acre during a lightning storm. In reality, there is no such thing as “synthetic” nitrogen fertilizer or for that matter phosphate, potash or anything else. The term synthetic fertilizer is merely a belief, certainly not a fact.

Nitrogen fixation

Nitrogen-fixing crops of concern to prairie agriculture include alfalfa, clovers of all kinds, dry beans, faba beans, lupins, soybeans, peas, chickpeas, lentils and a few other crops. Legumes generally grow in nitrogen-poor soils, where their ability to fix nitrogen with bacteria gives them a competitive advantage over other competing crops or weeds. Adding nitrogen to a legume crop will remove that growth advantage and also inhibit the legume from forming effective nitrogen-fixing associations with the appropriate bacteria.

When I was a child in Wales in the 1950s, my father would plant red clover crops every third or fourth year. Selective weed control products were non-existent in those days so he would underseed a light crop of wheat with a clover-grass mixture after first fertilizing with phosphate and potash and some sulphate — no nitrogen. After he took off a light wheat crop in August, about 15 to 20 bushels per acre, we would get a huge growth of red clover by October. Undoubtedly, after it was plowed under at the end of the second year, there was a two- to three-year supply of nitrogen in the soil from the clover crop’s nitrogen fixation.

Nitrogen-fixing legume bacteria which we call rhizobia are characterized by their ability to infect the root hairs of legumes. These rhizobia live freely in all agricultural soils in a living active vegetative state. They do not form resting spores. These soil-dwelling rhizobia use sugars and soil acids as their sources of growth and energy. If there are wild legumes such as vetches around your farm, or stray alfalfa, they will be naturally inoculated by wild rhizobia in the soil.

Rhizobia species are generally divided into six major groups for agricultural purposes.

• Rhizobium meliloti: alfalfa and lotus types
• R. trifolii: clovers of all kinds
• R. leguminosarum: peas, faba beans, lentils
• R. phaseoli: dry beans
• R. lupini: lupins
• R. japonicum: soybeans

These rhizobial bacteria are easily propagated in laboratory culture and are generally very specific to the type of legume that they infect and nodulate. For example, Rhizobium leguminosarum can form a nitrogen-fixing partnership with peas, faba beans or lentils but not dry beans or chickpeas.

Soybeans, native to China must be inoculated with Rhizobium japonicum, which, like other rhizobia, are mixed in peat, peat pellets or liquid formulations. The soybean inoculant may not survive our Prairie winters, so to fix 60 or so pounds of additional nitrogen, soybeans may have to be inoculated every year.

On the other hand, R. leguminosarum is ever-present and adapted to Prairie soils, so if you grow peas, lentils or faba beans every few years your soil may have adequate nodulation bacteria to fix 50 to 150 pounds of “free” nitrogen. If you forget to inoculate peas, faba beans or lentils they will nodulate anyway, as you have grown them recently in that field. However, researchers have developed more specific strains of rhizobia — it’s often well worth the purchase price to have additional nitrogen fixation by these superior strains.

If you regularly grow peas or lentils you should leave a check strip with no inoculant and check the nodulation and or yield. Active nodulation is generally close to the main root and the healthy nitrogen producing nodules are a red/pink in colour when sliced open.

Effective inoculants on pulse crops or alfalfa hay can fix 50 to 200 or more pounds of nitrogen per acre. Just work out the cost savings on nitrogen fertilizer on a section of land.

Never do this with inoculant

Buying rhizobial inoculant is like buying a bunch of cut flowers. You wouldn’t leave the cut flowers in the truck cab on a sunny day, and you wouldn’t let them sit for weeks or months before bringing them into the house. Instead, you put them in a vase of cool water as soon as possible.

• NEVER leave inoculant of any kind sitting in the truck cab where the high temperature of 40+ C will quickly kill off the rhizobia.
• NEVER let the inoculant sit around for weeks or months on end before use. Store it in a cool refrigerator to keep the rhizobia alive and healthy.
• NEVER use last year’s inoculant. The rhizobial bacteria are likely all dead.
• NEVER mix inoculant with a seed treatment or micronutrient that contains zinc or copper.
• NEVER leave a liquid inoculant for many days on unplanted seed.
• NEVER skip an inoculant application if you grow soybeans on the prairies.

Remember, rhizobial inoculants are living, breathing fragile bacteria. You need to keep them fully fresh and active for best results.

The post Why soybeans need inoculant and how some crops fix nitrogen without it appeared first on Grainews.

Precision agriculture tools are improving the accuracy of where fertilizer is placed so that as much of it as possible reaches the plants that need it.

And researchers from at least two Canadian universities — Ottawa’s Carleton University and Western University in London, Ont. — are working on smart fertilizers that only deploy when the plants are in need of nutrients.

The latest approach is developing crops that can fertilize themselves. It’s something that life sciences giant Bayer is betting heavily on — the German multinational recently announced a new partnership with Boston-based biotech start-up Ginkgo Bioworks to create a new company focused on the plant biome.

The goal of the yet-to-be-named company, funded through a US$100 million investment by Bayer, Ginkgo and U.S. hedge fund Viking Global Investors, is to lessen dependence on chemical fertilizers by letting plants create their own.

Here’s how it works

Legume crops like beans, peas, lentils, soybeans and peanuts can fix nitrogen naturally. They attract bacteria called rhizobia that form little nodules on a plant’s roots and then work to convert free nitrogen from the air and soil into ammonia. This helps the plant feed itself without needing any — or as much — added fertilizers.

Other crops like corn, wheat, and rice — some of the world’s leading staple food crops —aren’t attractive hosts to the nitrogen-fixing microbes, making their fertilizer needs pretty high. Not only is this expensive for farmers, but there are environmental impacts, too, ranging from carbon emissions to algal blooms.

The Bayer/Gingko partnership is hoping to create what some are calling designer bacteria: developing nitrogen-fixing microbes that are attracted to the roots of any plant (not just legumes) so that they can be attached to wheat or corn seed, for example, through a special coating.

It won’t be an easy undertaking, though.

Scientists will need to search through hundreds of thousands of bacteria to find potential microbes for sequencing in an effort to determine which genes are behind nitrogen-fixing activity. Once those are identified, they can be used to develop custom DNA for new, scientifically designed bacteria. There’s no certainty, however, on how those microbes will react once they’re outside the lab and exposed to the complex soil environment.

If successful, this could be a game changer for agriculture with significant impacts on global fertilizer markets. According to market research reports, the value of the global nitrogenous fertilizer market was pegged at over US$107 billion in 2016, with expectations that this will reach approximately US$127 billion by 2021.

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So why, anecdotally at least, does the practice seem to be on the increase?

Bigger farms and a shortage of labour could be part of it. Moreover, nobody knows when poor weather will shut down field operations. And there’s Manitoba’s Nov. 10 nutrient application deadline — a regulation meant to prevent fertilizer from being applied on frozen ground, making it more susceptible to run-off, which can contaminate waterways and lakes.

But broadcast nitrogen, especially in warmer soils, or soils that later become saturated, can be lost to the atmosphere, adding to the greenhouse effect and climate change.

With the Manitoba government close to announcing its climate change policy, which will include a price on carbon, some observers worry fall nitrogen broadcasting could trigger additional regulations.

“The Manitoba Fertility Guide… shows an average of 40 per cent less efficiency for N (nitrogen) fertilizer that’s broadcast in the fall, compared to banded in the spring,” University of Manitoba soil scientist Don Flaten said in an email Oct. 5. “This issue of poor efficiency of fall broadcast N is even worse if the soils are waterlogged in early spring.

“For fall banding N, it’s important to band as late as possible, especially for low-lying areas of fields that might be ponded with water during snowmelt.”

In a perfect world farmers would band nitrogen in the spring nearest the time it will be used by crops. But then there’s the art of the possible. There are only so many hours in a day and the weather has to co-operate.

If spring banding gets the gold medal, other techniques and timings have varying results, Manitoba Agriculture soil fertility specialist John Heard said in an interview.

“Banding has a distinct advantage over broadcasting,” Heard said. “There’s a big advantage of spring over fall application, especially with wet falls and springs. The real loser in the story is fall broadcast. Even worse is fall broadcast early in the fall on warm soils.”

Last week one field Heard checked was 15 C at three inches deep.

“If soil was to stay at 15 C, (fall) banded urea could convert entirely to nitrate within 25 days or so,” Heard said. “It means by freeze-up a sizable portion of that (nitrogen) would be in the nitrate form, which could be very vulnerable to leaching or denitrification.”

Benefits of banding

When nitrogen is applied it’s in the ammonium form, it’s stable. It has a positive charge and locks on to clay and organic matter. But warm soil bacteria are more active converting ammonium to nitrate, which can be used to nourish plants, but also be lost to atmosphere.

Banding nitrogen in cool soils helps avoid those losses in a couple of ways. One is bacteria are less active then. Another is the band itself is toxic to bacteria, although over time the conversion to nitrate occurs.

“If you apply (nitrogen) later (in the fall) the microbial activity is thwarted,” Heard said. “If you apply it in a band you further thwart that bacterial activity promoting conversion to nitrate.”

Many farmers like to apply anhydrous ammonia in the fall because it’s usually cheaper than other forms of nitrogen. Heard said it’s a good choice because that form requires in-soil banding. Farmers who apply anhydrous ammonia or urea nitrogen early can slow the conversion to nitrate with various nitrogen conversion inhibiters, he said.

Another disadvantage to broadcasting nitrogen is having it get tied up with crop residue called immobilization. That’s not an environmental concern because eventually that nitrogen will be available to future crops. The problem is a portion of it may not be available for early-season crop growth.

Not only is fall broadcast nitrogen vulnerable to losses in the fall, but in the spring too.

“If the soil is saturated we know that we can lose nitrate-N, even in the spring when the soils are quite cool, two to four pounds of nitrogen per acre, per day,” Heard said.

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Pulsea crop growers are no doubt familiar with BASF’s Nodulator and Monsanto BioAG’s TagTeam pulse crop inoculants. They’ve been around for years.

For the 2018 growing season BASF is introducing Nodulator Duo, a product that adds a soil bacterium to the inoculant. It has the ability to enhance and strengthen root development.

Monsanto BioAg last year introduced TagTeam LCO which is a triple action granular inoculant. The LCO component, short for lipochitooligosaccharide, is a natural soil molecule that “enhances” communications in the root zone improving the nitrogen fixing performance of the rhizobium.

Both are granular products to be used with pea and lentil crops.

New from BASF

Early field trials with Nodulator Duo (2017 yield results are not in yet) show including the bacterium with the inoculant produced on average a three bushel yield increase with peas and about a 1.5 bushel yield increase with lentils, says Russell Trischuk, BASF regional technical manager.

“BASF has development projects in different parts of the world,” he says. “And Nodulator Duo is truly a made in Canada product for Canadian producers. We are very excited about that.”

The “duo” is a combination of the Nodulator rhizobium and a strain of bacterium (Bacillus subtillis) identified as BU 1814. They are combined in a solid core granule.

The activity of the bacterium is part of a fairly complex process involving soil biology. “When included with the inoculant in the seed row the native bacterium has a mutually beneficial relationship with the plant,” says Trischuk. “As the root grows and cells slough off and distribute through the soil, the bacterium feeds off those cells and in exchange they colonize the plant root system offering protection of the roots as they grow through the soil.” It’s called a root strengthening bio-film that enhances root and plant growth.

While that process isn’t directly connected to the activity of the nitrogen fixing rhizobium it does have a “very positive relationship”, he says. They’ve measured increased nitrogen fixation, increased nodulation and even the shape and location of the nodules is affected. While the N-fixing nodules usually form near the crown of the roots, the addition of BU 1814 seems to encourage nodulation in different areas of the roots.

What all this science means from a farmer perspective, says Trischuk is a more vigorous pulse crop plant stand, that flowers longer, stays green longer, produces larger pods and more pea and lentil seeds per pod. He says there is even some evidence of crops showing improved tolerance to stresses such as dry growing conditions.

Improved lines of communcations

Including the LCO component in TagTeam LCO improves communication between the roots and the rhizobium which is particularly beneficial under stressful growing conditions, says Jon Treloar, Monsanto BioAg technical agronomist. Their field trials, with peas for example, show up to 2.5 bushel yield increase over competing products.

“The LCO molecule is involved in communicating between the rhizobium and the plant roots,” says Treloar. “The molecule signals the plant roots to prepare for nodulation and nitrogen fixation. That molecule is naturally occurring and always present in the soil, but under stressful environmental conditions (being too cold, too wet, too dry, for example) that communication can be delayed. By adding it to the inoculant we are in essence short circuiting the natural communication process and speeding up nodulation.”

TagTeam LCO was introduced for the 2016 growing season. It showed improved yield performance over the conventional TagTeam and about a 2.5 bushel yield increase over other pulse crop inoculants.

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Other “beneficial bacteria” can be found in symbiotic relationships with crop plants that promote growth, increase stress or pest resistance, or increase nutrient solubility.

Only in recent years have scientists been able to point to specific bacteria that can perform specific services for crops, and “bottled” them and sold them. But this February, the biological crop protection market was forecasted to grow at a rate of 11.33 per cent over the 2016 to 2021 period, driven by “agricultural productivity as well as increase in demand for chemical free crop protection solution [sic],” according to a Research and Markets study.

There’s clearly a future in bacteria, and science and industry are capitalizing on it.

Bacteria in the lab

At Ze-Chun Yuan’s lab in London, Ont., the Agriculture and Agri-Food Canada scientist has been working on isolating beneficial bacteria for six years. His goal is to develop viable alternatives to chemical fertilizers and crop protection products that lessen the strain on the environment — and producers’ pocketbooks.

“On the plant pathology side, you have two ways to manage plant disease. You can use a pesticide, or you can use beneficial bacteria that can protect plants and maybe also produce some nutrients in the soil,” he says. “It’s a more natural process.”

Yuan’s program has seen some important successes. His team has identified three bacteria that have potential applications for crops. Paenibacillus polymyxa CR1 was the first of these to undergo complete genome sequencing by AAFC.

This bacterium not only fixes nitrogen and produces a growth-promoting hormone, it also produces chemicals that can potentially protect plants against diseases and pests.

But it’s only one of many bacteria that Yuan and his team are examining. “We have about 2,000, almost 3,000, bacteria isolated from corn and soybean roots or legume roots. We also have a lot from wheat,” he says. “We just got a new freezer!”

The bacteria Yuan is interested in produce what are called “endospores,” extremely resilient “packages” that contain the bacteria’s genetic material and can survive under harsh conditions. For agricultural applications, this is a big advantage, says Yuan. The endospores, which are a few hundred times smaller than their “parent” bacteria, can be mixed with powder and sprayed on crops or applied as biopesticide or biofertilizer seed coatings.

This summer, Yuan intends to test both methods in field trials on soybeans, corn and tomatoes. The trials will look at P. polymyxa CR1 as well as a handful of other bacteria.

The trials will be held at AAFC’s research centre in London, but Yuan wants to collaborate with as many partners as possible, including grower groups and organizations, to expand the research to other Canadian provinces.

It might take a few years before P. polymyxa CR1, or some of the other almost 3,000 beneficial bacteria in Yuan’s freezers, hit the market in product form. But Yuan is confident that they will. “We need a year or two to figure out what the best formulation is,” he says.

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That’s the advice from long-time Western Canada soil researcher Rigas Karamanos.

“With a wet fall in many parts of Western Canada which delayed harvest, many producers may not have got as much fall field work done as they would have liked,” says Karamanos, senior agronomist for Koch Fertilizer Canada. “And if products are available now, some producers might be thinking they’ll catch up on their field work and broadcast apply fertilizer over winter. It’s just not a good idea for a few reasons.”

First of all, nitrogen fertilizer that sits in snow or even on frozen ground for a few months could result in nitrogen losses as high as 40 to 50 per cent, says Karamanos. And depending on the blend and rate applied, come spring, winter-applied fertilizers could simply run-off the field and contribute to high nutrient levels in surface water.

Top dressing option

While getting crop nutrition applied before or at seeding may be preferred by many, Karamanos says, top dressing in-crop presents a viable option producers should consider, with no yield penalty.

Aside from the timing issue of getting everything applied at seeding, he says there may also be a real challenge this spring of finding sufficient supplies of fertilizer come April.

Karamanos says producers can apply what is needed to get the crop started at time of seeding, and then follow up during a four to six week window after seeding to get the remainder of the nutrients in the ground.

He says both liquid and granular products can be effective, applied in-crop as a top dressing. “You do need moisture, but assuming that’s there or coming, you can use any products quite effectively,” he says. “There is plenty of research that shows you can apply products in-crop and still optimize yields.”

With cereals it is important to apply top dress fertilizers by the first node stage (growth stage 31) and with canola, it should be applied by the sixth-leaf stage.

In applying a liquid fertilizer top dressing, Karamanos says it is important to use proper dribble band equipment (as opposed to a foliar spray system) to get nutrients through the standing crop and onto the soil where it is needed. “With liquid products, dribble applied, there might be some crop setback, but the crop will over come that,” he says.

He says it also might be a good year for farmers to consider delayed-release nitrogen fertilizer products, if they haven’t already. There are polymer-coated products as well as urease-inhibitor products that may have a fit as well. While he admits to being a bit partial to a Koch-carried product, Agrotain urease inhibitor, he says delayed or slow release products can be an effective way to manage field workload and reduce nitrogen loss under adverse conditions.

Karamanos says while there are a number of foliar products on the market, producers shouldn’t rely on them to supply sufficient macro-fertilizer ingredients such as nitrogen. At recommended application rates, they simply can’t deliver enough through a foliar treatment to make up for plant growth requirements.

So the take home message: don’t apply fertilizer on the snow, and if it doesn’t line up to get all nutrients applied at seeding, consider in-crop top dressing.

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But some agronomists suggest postponing application of a portion of N fertilizer until the crop is actively growing, when the crop is better able to utilize the nitrogen. Is “spoon feeding” a good approach?

Two key questions to consider in deciding if in-crop N application would benefit you are:

1. What are your potential N losses after seeding? And,
2. How can you efficiently apply in-crop N fertilizer?

Nitrate-N can be vulnerable to loss after heavy precipitation due to leaching, particularly in sandy soils. Very wet soil conditions can result in denitrification of N, particularly in medium and fine textured soils. Denitrification occurs in very wet, warm soils and is caused by soil bacteria striping oxygen from nitrate-N, converting it to gaseous nitrous oxide. Depending on soil and climate, significant N loss can occur in spring and early summer. But, if soil N losses are low between the time of fertilizing and beginning of July, the benefits of in-crop application will probably be low.

In-crop application

There are several ways to apply in-crop N, but none are ideal. Liquid 28-0-0 can be dribble banded or applied with spray jet nozzles. Urea (46-0-0) granular fertilizer can be broadcast. But remember, urea is subject to volatilization, so a urease inhibitor should be used to minimize volatilization (gaseous) losses when applied. Also remember that 50 per cent of N in 28-0-0 is in urea form and subject to volatilization. And, after application, rain must move the N fertilizer into soil. Once N fertilizer is moved into soil, it will take two to three weeks for the majority of the fertilizer to convert to nitrate-N for plant uptake. So, from the time of application to the time the fertilizer is available could be easily be three to four weeks. Therefore, for both in-crop broadcast 46-0-0 and in-crop application of 28-0-0, the very best efficiency of uptake would be 30 to 40 per cent, and would only occur if precipitation moved the fertilizer into the soil within a few days after application and the product was applied by late June. In a best case scenario, if 40 pounds of N per acre was applied with an uptake efficiency of 40 per cent, only 16 lbs. N/ac. would actually be taken up by the crop.

For foliar application of 28-0-0, the maximum application rate using spray nozzles is about 20 lbs. N/ac. to avoid leaf burn. Generally, less than five per cent of the applied N is taken up via the leaves in a best case scenario, which means less than one lb. of N/ac. of a 20 lbs. N/ac. application would be taken up the foliage, which is almost insignificant to increase crop yield. The N fertilizer would have to be washed from the leaves by rain and moved into the soil, then converted to nitrate for plant uptake. This method of application is not normally recommended, as the efficiency of uptake tends to be quite low.

Broadcast application of ammonium nitrate (34-0-0) is the best in-crop product with very little potential N loss. Half the N in the fertilizer is in the plant-available form of nitrate, which is immediately available to a crop after rain. Unfortunately, only a couple of companies import 34-0-0 in to Western Canada so availability is generally extremely limited. If you have access to it, 34-0-0 is an excellent N fertilizer for in-crop application.

If leaching or denitrification is not normally a problem, banding before seeding or preferably at seeding will result in the best efficiency of uptake for cereal and oilseed crops. In wetter regions, particularly in June, it may be beneficial to reduce N application in spring by 20 to 40 per cent and apply a split application about mid-June for availability in early July. Rates of 30 to 50 lbs. N/ac. will be necessary when application efficiency is 40 per cent or less.

In wetter regions with increased concerns of N losses, another option at planting is use a combination of urea and a slow release N fertilizer in a ratio such as 40:60 to reduce potential N losses. Studies by Alberta Agriculture with wheat, barley and canola with urea, ESN and a blend of urea/ESN have shown clear benefits using ESN when N losses are potentially higher.

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One option to consider is banding N fertilizer in late fall. But keep in mind that fall N application can range from very effective to very disappointing. Effectiveness depends on environmental conditions after application including soil moisture and temperature.

The products

The two best fertilizers for fall application are urea 46-0-0 CO(NH2)2 and anhydrous ammonia 82-0-0 NH3. When urea or anhydrous ammonia are banded into moist soil, both convert to ammonium NH4+. Ammonium is positively charged and is relatively immobile in soil and will not leach under wet conditions. In warm, moist soil, specific bacteria will convert ammonium to nitrate [NO3-] over a several week period. This process is called nitrification.

Nitrate is negatively charged, is mobile in soil and will leach with excess precipitation, particularly in sandy soils and can be loss to denitrification (gaseous loss of N in very, wet soil).

Banding ammonia or urea creates an environment within the band that slows the activity of soil bacteria that convert ammonium to nitrate, delaying nitrification. When urea or anhydrous ammonia are banded in late fall after the soils have cooled in temperatures less than 5 C to 7 C and micro-organism activity has slowed, most of the fertilizer N will be remain in the ammonium form over winter until the soil warms up in the spring. The ammonium form is relatively stable and won’t leach or denitrify.

If urea is broadcast and incorporated or banded in early fall when soils are still warm and moist, much of the ammonium can potentially be converted to nitrate before freeze-up. Excess precipitation in late fall or spring could then cause the nitrate to leach below the crop root zone, particularly in sandy soils or be lost due to denitrification. The denitrification process occurs when N fertilizer has converted to nitrate, soil conditions become very wet or saturated after snow melt in spring or due to heavy precipitation events. Soil N is lost when soil microorganisms in anaerobic conditions (very wet soil without oxygen) convert nitrate-N to nitrous oxide — a gaseous form of N that is lost to the atmosphere.

All soil types and regions of the Prairies are susceptible to losses of fall-applied N fertilizer. However, the risk of N loss is highest in regions with moister climates when soils can be very wet, such as the black and gray soil zones, and risk is lowest in regions that tend to be drier, such as the brown and dark brown soil zones.

Alberta research has shown that nitrate losses through denitrification in drier regions are usually low, and fall-banded N is usually equally effective to spring-banded N. But if spring wet conditions occur, N losses can still be high even in low risk regions, after heavy precipitation events. Each fall, a farmer must look at specific local environment conditions to weigh the risks versus benefits of fall fertilizer application.

Some issues to consider:

• Late fall-banded N can be as effective as spring banded N, if there is no extended period of very wet or saturated soil conditions in the spring.
• Early fall application of N fertilizer has a greater chance of converting to nitrate-N before freeze-up and would be more susceptible to N loss in the spring.
• Fall-banded N can be more effective than spring-banded N when springtime seedbed moisture is limited, and spring banding would dry out the seed-bed.
• Fall-banded N can be less effective than spring-banded N when spring moisture is wet for extended periods.
• Fall fertilization shifts workload from the hectic spring to the fall. This can increase spring seeding operation efficiency.
• Nitrogen fertilizer prices tend to be lower in the fall than in the spring, providing an economic advantage with fall versus spring fertilization.

It is wise to get opinions from soil and crop experts in your region including your fertilizer dealer, industry agronomist and government agronomist to consider all the pros and cons of fall fertilizing before you make your final decision.

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