Upholding Pulse Sustainability

Research demonstrates there is still a lot to learn about the link between pulses and sustainability

Growers already know that pulses have a lot to offer in terms of environmental benefits for their farm. Because they fix their own nitrogen and increase the diversity of soil microbes, pulse crops increase the health of the soil, which can also help increase the quality of subsequent crops. They also have a lower water and carbon footprint than other protein-rich sources. This is extremely important at a time when world demand for plant-based protein is rapidly increasing.

So what is left to learn about pulses and sustainability?

Well, actually a lot, says Dr. Lisette Mascarenhas, Director of Research and Development at Saskatchewan Pulse Growers (SPG).

Growers are aware of the benefits of growing pulses, but it is important to drill down deeper, so that we gain a greater understanding of why and how pulses benefit on-farm sustainability and how they can continue to do so in the long term.

"It has been known for a long time that pulses fix nitrogen and therefore the requirement for nitrogen fertilizer is lower in pulses than for other crops," Dr. Mascarenhas says.

"There has also been research in the past that showed pulses can actually improve the interactions between organisms that generate increased diversity in the soil, which means a healthier environment. We also know that pulses like lentils and chickpeas can tolerate drier conditions reducing the need for a lot of water, so collectively the overall message is that pulses are good for the environment."

"Now the focus is providing information, through studies over time, for how including pulses in various rotations are beneficial. We know pulses are good for the soil but we want to know how, exactly."

These themes fall under SPG's research priorities of increasing the production of pulses, and removing constraints to production in Saskatchewan. SPG has also partnered with other agencies that are committed to research in the area of sustainability, such as Agriculture and Agri-Food Canada, to leverage funding for projects that are important to Saskatchewan's pulse industry.

Through several ongoing research projects in this area, it is apparent that we are still learning about the important role that pulses play in on-farm sustainability.

Nitrogen Fixation ond Nitrous Oxide (Np) Emissions

Dr. Richard Farrell, an Associate Professor in the University of Saskatchewan's (U of S) Department of Soil Science, has been studying the relationship between pulses and nitrogen for many years, most recently leading a study that aims to clarify the relationship between pulse crops and N20 emissions.

"There has been concern that pulses, because they fix a Iot of nitrogen and return it to the soil, might have a higher nitrogen penalty associated with them," he says. "That was the question going into this research - is that actually true?"

"Right now, all the methodology used to calculate greenhouse gas (GHG) inventory assumes that all forms of nitrogen are the same. Whether ammonium nitrogen fertilizer, cattle manure, or crop residues, the emission factors for fertilizer apply to everything."

Farrell did not believe this was accurate, and his research, which is set to wrap up shortly, set out to prove this. To do so, he created a very controlled environment to measure the cycling of atmospherically fixed nitrogen by lentils, chickpeas, and faba beans, and the contributions of the fixed nitrogen to N20 emissions, as well as its uptake by a following wheat crop.

"We developed a greenhouse system that allowed us to feed plants in a nitrogen-enriched atmosphere so that any nitrogen that wound up back in the system had to have been fixed by the plants," he says. "This aIIowed us to look at the four pIants side-by-side to see how they performed."

During the next phase, the research team grew wheat in the same soils containing the pulse residues, and then tracked the residue-derived nitrogen and N20 produced.

The following year, the trials were moved out into the fields, growing the same crops and varieties in the same soils. The team then examined the above- and below-ground residues.

Although they are still pulling the data together, Farrell says there are some early results.

"What we are seeing is that the overwhelming majority of the emissions come from fertilizer," he says. "When you add fertilizer in, 90 per cent or so of total emission is fertilizer induced. It is clear that pulse residues are not the equivalent of fertilizer."

It is also clear that the below-ground residues contribute more than the above-ground residues, he says, and that the soil contributes only minor amounts.

"The data are really pointing to the fact that below­-ground nitrogen is really important and that we really do not have a good way of accounting for it," he says.

Overall,these early results mean the concerns about pulses and N 0 emissions have been overplayed, Farrell says.

"The preliminary data suggest that the emission factor for residues will be lower than emission factors for fertilizer," he says.

"We think because of all this below-ground nitrogen, we are gettinga bigger nitrogen credit from pulses than we are giving them credit for now. They also have a smaller contribution to N20 emissions than people thought they wouId."

Another interesting finding of this research had to do with faba beans, says Dr. Diane Knight, a co­ investigator on the project and a Professor in the U of S Department of Soil Science.

"Faba beans are thought to be one of the best nitrogen fixing crops, so growers are quite interested in it for rotations," she says.

In field trials, they saw nitrogen fixation rates for faba beans of around 70-80 per cent, the highest amount of all the crops observed.

Knight is also working on a different project that involves exploring the potentialof faba beans to cut down on the need for fertilizer requirements. Specifically, the study aimed to develop a collection of Rhizobium species isolated from different wild legume species, and test their effectiveness in nodulating the major pulse crops grown in Saskatchewan.

"We wanted to develop a collection of rhizobia that are from cold climates so that with climate change we will have access to a range of different rhizobia that may be better than what we have right now in commercial inoculant."

To facilitate this, Dr. Knight and her team collected many species of native legumes from around the province, as well as some from the Yukon.

"We are looking at the wild legumes to see if we can find Rhizobium that work really well but mostly because they are going to be adapted to the climate here. The ones from the Yukon are quite special - they are able to be quite metabolically active, especially in these cold climates."

Once they had developed their collection, they then isolated and purified the Rhizobium from the native legume nodules.

"We were basically identifying what plants have what Rhizobium In them, screening them against peas and lentils, and documenting whether or not they can nodulate and fix nitrogen in these different crop plants."

At this point in the research they have sent the DNA off for sequencing in order to identify the actual species of Rhizobium they are dealing with. Later this year, Knight hopes to be one step closer to having a resource available that is better adapted to the climatic extremes.

Optimal Tillage Practices

Another ongoing question in Saskatchewan agriculture is: What are the optimum tillage practices for increasing crop quality and yield, and maximizing economic returns?

Two ongoing studies funded by SPG are looking to help answer this question.

Knight is currently looking at the effects of a long-term, no-tillage system on the nitrogen balance in the soil. Previous studies aimed at calculating nitrogen balances have taken a larger, whole-system view, instead of a farm-by-farm view, Knight says.

"When looking at the whole system, researchers almost always come up with more nitrogen coming into the system than being lost - the nitrogen budgets do not balance."

Knight's project is examining if the gain in nitrogen is because of free-living nitrogen fixing organisms in the soil. Unlike Rhizobium, free-living bacteria do not need a legume plant to fix nitrogen. These organisms are plentiful in native prairies.

Knight and her team suspect that as soils are managed with no tillage, the soil microbial populations begin to convert back to those populations similar to native prairies. The higher nitrogen inputs compared to outputs may be a result of increased numbers of free­-living nitrogen fixing organisms due to the conversion to no tillage.

To measure this, Dr. Knight and her team have looked at growers' fields that have been under no-tillage management for different lengths of time, some up to 25 years, to see If there was an Increase In free-living nitrogen fixation.They also examined some native prairie sites, in which all the nitrogen comes from either free-living nitrogen fixation or wild legumes, to use as their baseline example of how much free-living nitrogen fixation might be present in the soils.

At this point it is too early to have any concrete results, but Knight feels that once the study wraps up later this year, there will be some practical takeaways that will help pulse growers adjust their fertilizer management and potentially cut back on their added nitrogen levels.

Another ongoing study in this area is looking at the effects of vertical tillage on soil structure and crop yields in southern Saskatchewan.

The project began in 2015 and is led by Dr. Bing Si, a Researcher and Professor in the U of S Department of Soil Science, with expertise in soil physics. The study compares the effects of different pre-seeding tillage treatments, such as vertical and conventional tillage, raking and burning, as well as direct seeding into flax stubble.

The crops involved in the research include wheat and peas, says Dr. Jeff Schoenau, Professor in the Department of Soil Science, who is also one of the researchers on the project.

"In terms of the different tillage treatment effects we compared, we really did not see any significant differences among the treatments on yield of wheat grown in the first year," he says, adding that it is still early in the study.

"For effects on soil physical properties, one effect we did see was that vertical tillage tended to result in slightly lower air permeability, which is the ability of air to enter the soil, than  the disk treatment. The action of the rolling basket might have increased the proportion of fine pores in the soil,'' Schoenau says.

This research is set to wrap up in 2018, after two more field seasons are completed.

Water Footprints

One issue that has become important for agriculture recently is that of water footprints, in other words, how much water is required to produce specific quantities  of each crop.

This issue is only going to increase in importance in coming years, says Si.

In order to get ahead of the curve on the issue of water footprints for Saskatchewan agriculture products, Si is currently facilitating research that will quantify and compare the water value for Saskatchewan-grown canola, wheat, and pulses.

The research will also test whether or not pulses grown in a rotation have the ability to improve the water footprint for the overall rotation, as nitrogen production requires water and pulses reduce overall nitrogen input into the soil.

The research is only about halfway complete, but Si is optimistic that the results will yield good news for the pulse industry.

"We expect that when you consider everything in a comprehensive way, you would have at least a reduction of water footprint per unit of grain yield," he says.

He also expects the research will offer concrete evidence that pulses offer protein at a lower water cost.

"Consumers are interested in protein and pulses have a high protein content, so if our purpose is to produce a large amount of protein per unit of water consumption, then we can show that pulse crops would be the way to go," he says.

Si's research will wrap up in late 2017.

Rotations

It is generally known that it is good to include pulses in your crop rotation, but ongoing research is drilling down into deeper questions, such as exactly which crops are best to grow in sequence.

Knight is involved in some preliminary work looking to identify soil characteristics that impact biological nitrogen fixation in pea and lentil crops grown after canola.

"One of the things I do in most projects I am involved in with rotations is measure nitrogen fixation," she says. "What we found in Swift Current is when we grew peas or lentils right after canola, it did not fix nitrogen to the same degree as if we grew it right after wheat in a rotation."

Other areas of the province did not seem to show the same problem, Knight says, but Swift Current did so consistently.

"There seems to be some inhibitory thing happening with the canola affecting the pea crop," she says.

Although it is very early in the research, Dr.Knight has a theory as to why, and it involves the level of organic matter in the soil.

"Soil organic matter often acts as a buffer against bad things happening. In the Brown soil zone, where Swift Current lies, there is not as much soil organic matter as in other soil zones."

This research is set to wrap up in 2020, and Knight hopes to have more information at that point to help pulse growers inthe southern part of the province make better rotation decisions.

Other SPG-funded research is looking at developing more systematic approaches to minimizing the negative environmental impacts of crop production, while also increasing crop yield and overall farm economics.