A University of Alberta researcher who studies adaptive multi-paddock grazing says practice can benefit pasture soil
Scientists have found a type of grazing for cattle that can boost the movement of water into prairie grassland soil, which helps build drought resistance, but a researcher says the conclusion is only part of the total picture.
“I think it’s the nature of ecosystems,” said Timm Dobert, a post-doctoral fellow in the Faculty of Science at the University of Alberta.
“It’s so difficult to come up with very clear findings — oftentimes, it’s very complex. Sometimes you find that different parameters are working simultaneously.”
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Dobert was part of the first large-scale research project to examine the impact of adaptive multi-paddock (AMP) grazing on grasslands in Western Canada. The practice involves dividing fields into many smaller paddocks.
Cattle are rotated through each paddock for short periods at high grazing intensities, which is followed by long periods of rest for the land, allowing vegetation time to regrow. Although more than 80 percent of ranchers are using some form of rotational grazing in Canada, only about five to 10 percent likely practise AMP grazing, said Dobert.
The research project was launched under the Agricultural Greenhouse Gases Program of Agriculture Canada. A team of about 15 scientists spent five years from 2017-21 studying various aspects of AMP grazing, which is also known as holistic grazing management.
Scientists examined ranches from Alberta to Manitoba ranging from mixed-grass prairie to parkland. They were paired with neighbouring operations that didn’t follow the practice, with a total of up to 64 ranches taking part in the project.
Dobert said AMP ranches had about a 30 times higher ratio of rest to grazing. They also had a livestock density per paddock that was about 20 times higher, even if it was only as little as one or two days until the animals were moved to the next paddock, he added.
A study led by Dobert found extended rest periods improved infiltration of water into the soil by 30 percent compared to neighbouring ranches. Infiltration is the ability of soils to allow water to enter from sources such as rainfall or irrigation.
“So, that’s not so much AMP versus non-AMP, but it’s just, generally speaking, it’s good to have extended rests on the land for water infiltration.”
However, the high stocking rate of AMP grazing had a minimal to opposite effect on infiltration, he said. “In fact, there was even a trend that when animal numbers were increased, there was less water infiltration, so this allows us to tease apart a little bit the different components of AMP grazing.”
It supports the common idea that grazing at low to moderate stocking rates is better for the health of grasslands, he said.
Much of the Canadian Prairies experienced heat waves and drought last summer, causing shortages of feed for cattle and forcing producers to sell part of their herds.
“The western grasslands are an ecosystem that is water limited, so if we can identify on-field management changes, which are fairly easy to implement, and then have such a strong benefit for water infiltration, this will provide ranchers with potential strategies to better adapt to a changing climate,” said Dobert in a university statement.
However, giving advice to individual producers is “always a tricky question” for scientists, he said in an interview. “I think the most we can achieve through the sciences is really to stimulate ideas of what could be done differently.”
Each ranch is unique in terms of its climate, soils, and whether it contains native grassland or it’s been cultivated, said Dobert. However, there has been anecdotal evidence that AMP grazing promotes the buildup of organic carbon in soils via vegetation, he said.
The practice has been touted as potentially mimicking grazing by bison before they were nearly hunted to extinction in the 19th century, he said. Bison helped protect and sustain native grasslands and were a potential factor in the creation of deep layers of soil across the Canadian Prairies, he added.
“So, can we achieve more regenerative grazing, or more sustainable grazing, if we’re implementing grazing techniques which really mimic those bison a little bit more closely?”
Some estimates suggest that grasslands worldwide contain about 30 percent of global terrestrial carbon stocks. Because AMP grazing could potentially act as a natural way to capture greenhouse gas emissions from the atmosphere and store it in grassland soil, it has been “proposed to be the fix for the climate change dilemma,” said Dobert.
The research project found that organic carbon in the soil seemed to increase when there’s more cattle on the land combined with longer rest periods, “so this is different from what we found (for) water infiltration,” he said.
He cautioned the finding has not yet been peer reviewed or published in a scientific journal. “It can get more complex, but you can see it’s different parameters that work simultaneously.”
For example, researchers looked at whether there was any variation between shallow and deeper layers of soil. “And we did find there’s conflicting trends, so at the shallow soil, there was more soil organic carbon being stored in the soil,” he said.
“But then, if we looked at deeper soils, we did find the opposite trend, so there might actually be a tradeoff. So again, it’s fairly complex.”
A study co-authored by Dobert found higher cattle numbers on the land generally led to increased CO2 emissions regardless of the grazing method. And although experiments in the lab found methane uptake was 1.5 times greater in soils from ranches that used AMP grazing, no difference was detected during testing out in the field, he said.
Such results demonstrate that greenhouse gas fluxes generally differed little between grasslands where AMP grazing is practised and those where it isn’t, he said in an e-mail. Greenhouse gases are instead “regulated by specific conditions such as cultivation history, cattle stocking rate, soil moisture content, and bulk density.”
Grasslands cover more than 30 percent of the land on Earth and provide critical ecosystem services, helping to safeguard wildlife and mitigate climate change, he said in the statement.
However, large tracts of grassland in Western Canada have been lost to conversion to agriculture in the last two centuries, with the remainder mainly used to graze livestock.
“We lose an enormous amount of soil carbon in the conversion process,” he said. “You can point the lever in the right direction, but it’s really protecting the grasslands in the first place that is so critical for avoiding additional CO2 emissions.”
Dobert also said the backdrop of the research project is to establish the science that can be used to develop carbon offset protocols. The project is likely to eventually spark about 10 to 15 separate scientific papers, he said in the interview.
