[UPDATED: April 2] Thirty years ago Dr. Bart Lardner’s research focused on production efficiency. More recently, the researcher and professor at the University of Saskatchewan says his research program has moved toward ways the beef industry benefits the environment.
His presentation last November at the Canadian Forage and Grassland Association’s 14th annual conference in Harrison Hot Springs, B.C. focused on how pasture management builds soil carbon and reduces methane emissions from ruminants. Lardner said he looks at grazing as a necessary disturbance that, with proper planning, makes plants healthier.
“The plant needs to be defoliated. If you let it go reproductive, it’s going to obviously have a short lifespan. If we come in there and utilize a certain percentage of that above-ground biomass, we’re going to stimulate new regrowth (and) we’re going to get greater yields throughout that growing season, versus not coming in there and utilizing it, so it’s a positive disturbance.”
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Lardner said grazing stimulates cell division and growth of new tissue both above and below ground. It allows the reproduction of species that don’t produce seeds every year.
Lardner said organic matter below ground depends on what’s happening above ground. Stocking rate, intensity, timing, frequency and duration of grazing can all make a difference.
“Once we get beyond taking 50 per cent of above-ground biomass, and we increase that to 60 per cent above-ground biomass, we have a negative effect on below-ground root biomass. You need to leave some of the leaf out there. That obviously can impact on soil organic carbon levels, but also the quality of that forage impacts the level of enteric emissions.”
Lardner said overgrazing has a long-term effect. Research on native range near Saskatoon showed that overgrazed northern wheatgrass needed a 20-year rest. Overgrazing from higher stock densities also affects soil aggregates and water infiltration.
“Those porous spaces have to be open to utilize some of that water. Obviously we just see what’s happening above ground, but there’s a lot of effects of below-ground biomass… that we need to consider going forward.”
Lardner said there needs to be an equilibrium between adequate soil formation and a balance of soil organic carbon.
“That’s going to be somewhere where we take that improper stocking rate and decrease it to the point where we find the balanced approach. Thus, we’re starting to increase cover litter, soil organic matter and soil organic carbon.”
Forage quality and methane
Lardner said the most effective strategy to reduce enteric emissions in an extensive grazing system is to look at the quality of the forage, and the best way to improve it is by adding legumes.
Lardner cited research by Dr. Paul McCaughey at Brandon, Man. It revealed that cows on alfalfa-grass versus straight grass pasture produce less methane. He also noted similar results with his own research on non-bloating tannin legumes such as sainfoin and cicer milkvetch.
In recent years his research program has shifted toward measuring what’s coming out of the front of the beef animal. One way is by using a sulphur hexafluoride (SF6) technique where collars on steers measure the levels of methane and carbon dioxide two or three times throughout the grazing season.
He also uses C-Lock Inc.’s GreenFeed system, which involves attracting cattle to trailers in the pasture where they must keep their heads in the chamber for approximately two minutes to capture the nasal vapour to measure methane and carbon dioxide.
Feed ingredients and soil characteristics
Lardner said feed supplements can also reduce enteric emissions. This is easier in a feedlot or backgrounding situation than in an extensive system but researchers are testing various ingredients. Some had a minimal impact but others produced more methane. Work continues to find which feed ingredient will work the best.
Since 2018, Lardner has been conducting a long-term study of two perennial and two annual forage systems at the Livestock and Forage Centre of Excellence at Clavet, near Saskatoon. His team
is using data to study several characteristics including forage biomass and quality, animal performance, soil moisture and enteric emissions.
They are also partnering with a soil microbiologist to look at what’s going on below ground with the soil microbiome, and economists are conducting some system analysis. All four systems include a nitrogen-fixing legume. The two perennial systems include meadow bromegrass plus sainfoin and hybrid bromegrass plus alfalfa. The annual systems include fall rye plus clover and a simple polycrop mixture.
The researchers looked at the nutrient supply and microbial biomass, carbon and nitrogen. Plant Root Simulator soil probes measured potassium and nitrogen levels. Of the four systems, the hybrid brome alfalfa perennial system came out the winner in terms of nitrogen and potassium. It also came out ahead for microbial biomass carbon and nitrogen because of the perennial legume in the stand.
Access to the recording of Lardner’s session, as well as the other sessions at the CFGA’s 14th annual conference, is available for purchase. For more information email [email protected].
