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In the study, says Guillermo Hernandez Ramirez, researchers want to see if they can manage the nitrogen fertilizer input to reduce nitrous oxide emissions. (Photo: Janet Kanters)

Comparing New Nitrogen Alternatives

Alberta’s Russet Burbank growers are very experienced in managing nitrogen fertilizer for successful crops. Could some new products not only maintain tuber yield and quality but also reduce nitrogen losses to the air, enhancing the crop’s nitrogen use efficiency and sustainability? A two-year study aims to answer that question.

Nitrogen use efficiency is a topic that is an intersection of food security, environmental sustainability and economics in our agricultural production systems. We need to use nitrogen to produce a good harvest.

So says Dr. Guillermo Hernandez Ramirez, the study’s lead investigator and an assistant professor in the Department of Renewable Resources at the University of Alberta.

“However, by using nitrogen fertilizer we also have the risk of losing some of that nitrogen to the environment – to water or the atmosphere or other potential sites where excess nitrogen can become a pollutant. Also, we need to use nitrogen for profitable production,” he adds.

“Looking at nitrogen use efficiency helps us to have a conversation with farmers, scientists, agronomists and others, and it brings together all our good intentions about how to improve our production systems.”

Nitrogen losses to the atmosphere are a waste of nitrogen fertilizer inputs, plus those losses can be in the form of nitrous oxide, a potent greenhouse gas. “In this research, we want to see if we can manage the nitrogen fertilizer input to reduce nitrous oxide emissions,” he explains.

“We have been working on this issue for a wide variety of crops – wheat, barley, rye and others – around Alberta and in other jurisdictions. In the case of potato, this research is especially important because of the high input of nitrogen and other management practices, such as irrigation, which could affect nitrogen transformations and losses.”

Hernandez Ramirez is collaborating on the potato study with Dr. Michele Konschuh, Alberta Agriculture and Forestry’s potato research scientist.

“If you’re looking at crops with a big nitrogen impact, potato comes up. Alberta’s potato industry is predominantly processing potatoes, and processing potatoes in particular like nitrogen in order to get the yield and quality that processors require,” she notes.

This study, which started in 2017, is funded by the Potato Growers of Alberta and the Alberta Crop Industry Development Fund. The University of Alberta and Alberta Agriculture and Forestry are providing some in-kind support.

Potential Alternatives

In this research, Hernandez Ramirez is evaluating several nitrogen options that have never before been tested in Canada, including a fertilizer, a nitrification inhibitor and a biostimulant. The goal is to provide more information to help growers in making nitrogen management decisions.

“Perhaps there is some agronomic benefit from using these alternatives, or perhaps there isn’t,” he says. “And if there is an agronomic benefit, it has to interplay with economic considerations in the grower’s fertilizer decisions.”

The study includes the fertilizer product ammonium sulphate nitrate (ASN). Hernandez Ramirez says ASN is available in Western Canada, but there is no information comparing ASN to other fertilizers. His study is comparing ASN with urea, which is the nitrogen source most commonly used by Alberta potato growers, and Environmentally Smart Nitrogen (ESN), a slow-release, polymer-coated urea which is readily available in Alberta.

“Ammonium sulphate nitrate is becoming a more common fertilizer in Europe. We wanted to test it here because different weather conditions can influence fertilizer performance,” he explains. “Ammonium sulphate nitrate provides the benefit of a high nitrogen concentration, and it has the two forms of nitrogen that the plant can use – ammonium and nitrate. It is also a source of sulphur which could have some benefit for potato.”

According to Hernandez Ramirez, biostimulants are even newer to the marketplace than nitrification inhibitors and are not as well understood. Biostimulants include a wide variety of biological or biologically derived products that are used to improve crop growth and yields. The study is testing a soil-applied product called HYT A, which is not available in Canada.

“This biostimulant is a liquid containing a mixture of different microorganisms,” he notes. “Some of these microorganisms are able to enhance the decomposition of organic matter to make it into ammonium, which is available for plants to use. And some of the microorganisms are also able to fix nitrogen from the air and make it available to the plant in the form of ammonium. So the biostimulant has those two different functions.”

Adventures in Data Collection

Konschuh and her team are conducting the study’s fieldwork, which is taking place in irrigated plots at Brooks and Lethbridge. At each location, they have 11 treatments: urea by itself; urea with HYT A; urea with DMPSA; urea with HYT A and DMPSA; ASN by itself; ASN with HYT A; ASN with DMPSA; ASN with HYT A and DMPSA; HYT A by itself; ESN by itself; and a check with none of these nitrogen-related products.

The nitrogen fertilizers are applied at 80 per cent of the recommended rate to make it easier to see any differences between the treatments. The urea and ASN are applied as split applications, with two-thirds at preplanting and one-third at hilling. The ESN is applied in a single application at preplanting. The DMPSA is impregnated on the fertilizer granules so it goes on with the fertilizer. The HYT A is surface applied to the soil after the fertilizer is incorporated.

Konschuh’s team is monitoring nitrogen in the soil, potato plants and gaseous emissions. It’s pretty intensive work, especially with 11 replicated treatments at two sites.

“We take soil samples using a sampler that you push into the soil with brute strength, give it a twist and pull up a sample core,” says Konschuh. “In this study, we are taking a number of cores for each of the treatments at several times in the season. Plus we’re sampling separately in the hills and the furrows, which doubles our workload. So it’s really good arm exercise – it works those triceps.”

To track nitrate levels in the canopy, they use petiole sampling. “Growers here are accustomed to looking at nitrogen numbers from petiole sampling so they like to see that data. Typically, the amount of nitrate in the fourth petiole is an indication of whether or not the plant has adequate fertility,” she explains.

“For this study, we are doing petiole sampling three times per season. We take 60 to 80 petioles from each plot, which involves tearing a leaf off the plant and stripping leaflets off of the leaf’s main stem and collecting those. So it’s labour intensive and gives you very green fingernails.”

To quantify the amount of nitrogen lost to the atmosphere, they are collecting gas samples. “Weekly, we place the gas chambers on the hills and furrows. Then in a timed fashion, with a stopwatch around their necks, staff take samples from each of the treatments,” says Konschuh.

“That involves high-stepping over the hills and contending with ropy vegetation. We also have some logistics to work around including the lateral through the Brooks site and the sprayer tramlines at Lethbridge, so we have to deal with distance between the plots as well. All of those things limit how quickly you can take the samples. So the staff get their stopwatches going, start taking samples and trot along quickly.”

Initially they were taking three rounds of gas samples from all 11 treatments each week, but that proved to be impractical given the study’s protocol for the length of time between samples, so they have reduced the sampling scheme somewhat.

“Crazily enough, two of the people who helped with the gas sampling last year are willing to do it again this year,” Konschuh says with a laugh. “Either they are suckers for punishment or desperate for a job or really dedicated employees.”

Data loggers automatically monitor soil moisture and temperature, and Konschuh’s team harvests the potatoes using a machine, but grading is hands-on. “We grade the tubers into french fry categories, so each potato is individually weighed and categorized and counted. We also assess tuber quality, measuring things like specific gravity.”

Hernandez Ramirez’s team at the University analyzes all those soil samples for ammonium and nitrate, and determines the contents of all the gas samples. The petiole analysis is outsourced to a private lab in Lethbridge so the results will be consistent with what growers typically receive.

His team is also conducting controlled environment experiments to better understand the effects on nitrogen transformations of the nitrification inhibitor and the biostimulant under various conditions.

Initial Observations, Implications

Hernandez Ramirez is waiting until he has two years of data before drawing any firm conclusions or making any recommendations. However, his team has been testing DMPSA with other crops as well as potatoes, and the results so far are promising in terms of its agronomic and environmental effects.

He emphasizes it’s very early days in the evaluation of HYT A. “We are just trying to test it, with some effect in some cases and in other cases we don’t see an effect. We are still learning how this could be useful for producers.”

Konschuh adds, “[Using a microbial biostimulant] is a bit of a shot in the dark in the sense that we’re not all that knowledgeable about the microbial community in these soils. We know there are lots of microbes, beneficial and otherwise, and we know some of them work together and some of them aggravate one another. But in terms of which specific organisms are there or what happens when you introduce new organisms to that community, I’m not sure we really have a handle on that. Some of these biostimulants, especially ones that are produced elsewhere, may have been developed for different population interactions than we have here.

“The ASN and DMPSA would be easy for growers to use, if they want to adopt those strategies,” she adds. “The ASN product Guillermo supplied from Europe comes in a fertilizer prill. The DMPSA is easy for growers because it is already on the fertilizer. The biostimulant is less easy to use because it requires a separate pass and because it has to be handled so that it remains temperature-stable because there are live organisms in it.”

Although this study does not include an economic analysis, Hernandez Ramirez says other collaborators could easily use the study’s data to determine which options would make the most economic sense.

“This research is about sustaining potato productivity and trying to find ways to maintain soil quality for a crop that is very intense. In addition, improving the environmental performance of our production systems could help us keep access to markets and retain our social licence to continue to provide the goods and services from our potato production systems to society,” he says, adding using nitrification inhibitors could potentially generate carbon credits, so growers might be able to be paid for reducing the crop’s environmental footprint.

“We have a really good group of potato growers in Alberta and I think they are paying attention to concerns, environmental and otherwise, and they do the best they can [including carefully managing their nitrogen inputs],” says Konschuh. “If we can find fertilizer options that will do the job better than what we use now, then growers would probably happily move in that direction. But if the fertilizer program that the growers are using is working well and another one would also work well, then – unless the other option was also less expensive – I’m not sure what would motivate them to change their fertilizer regime.”

Hernandez Ramirez says this study has given him the opportunity to connect with potato growers and to learn a lot from them. “We look forward to being able to provide not only the best agronomy but also the best environmental management that we can find for this beautiful crop.”

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