Researchers make case for grassland benefits

Carbon sequestration, soil health, water quality and pollinator habitat could be used to justify paying producers

MONCTION, N.B. — A stronger case for maintaining Canada’s shrinking grasslands is being made by researchers.

“Our long-term goal is to recognize and quantify the magnitude the ecosystem goods and services these grasslands supply,” said Ed Bork of the University of Alberta and Mattheis Chair in Rangeland.

An army of scientists is working on the benefits beef production lends to carbon sequestration, soil health, water quality and pollinator habitat on Canada’s grasslands.

“We are trying to make the argument that grassland managers and cattle producers should be paid for some of the lesser known environmental goods and services other than forage production or beef production,” he said.

Researcher Denis Angers of Agriculture Canada in Quebec focuses on Eastern Canada, where carbon stores are being rapidly depleted.

Before European settlement and land cultivation in North America, soil carbon content was in balance in the forests of the East and prairies in the West, he said at the recent Canadian Forage and Grassland Association conference held in Moncton.

Cultivation caused a loss of 20 to 30 percent of the soil carbon.

“In the East, our carbon content is going down in general and that is basically because of cultivation of pasture and hay land,” he said.

More corn and soybeans are planted and 2.5 to five million acres of pasture and hay land have been lost in Eastern Canada in the last 50 years.

When perennial forages go back into the mix the carbon starts to rebuild.

“If you rotate perennials with annuals, you see an increase in carbon with long-term perennial crops, but it depends what you have in your rotation,” he said.

In Prince Edward Island, researchers established tall fescue stands and seven years later saw an improvement of about two tonnes of extra carbon per hectare (0.81 tonnes per acre) per year. Carbon was accumulated at fairly deep levels at about 50 to 60 centimetres.

Perennial forages aggregate the soil with dense root systems and microbial activity increases.

“It only takes two to three years to see a fairly dramatic effect,” he said.

Yields also improve, especially when mixtures are used because a diversity of roots develop at various depths.

“There is limited information on the effect of different species on soil organic carbon. We know putting in perennial systems will improve soil carbon but in terms of telling apart different species, we don’t know,” he said.

Perennials are well-suited to transfer carbon to the soil. They capture more solar energy annually because they start growing early in the spring and grow longer in the fall. They fix more carbon and release more into the soil.

Applying cattle manure on grasslands has a positive effect for soil carbon but grazing benefits are up for debate.

“Grazing is a tough one on the effect on soil carbon. We don’t have much data on the effect in a temperate climate,” he said.

International literature says decreasing grazing intensity can increase soil organic carbon but most data comes from tropical climates.

Bork’s results from research in Canadian plots have been different. He has 100 research plots in Alberta on public land and has also conducted research on former PFRA pastures in Saskatchewan, although most of the work is based in Alberta. He is investigating the effects of grazing and plant species.

In grasslands, the vast majority of the biomass is below ground. The root systems tend to be much larger than the shoot system above ground. It is the turnover of those roots over time that builds up large amounts of organic matter and carbon.

The vegetation removes carbon dioxide from the atmosphere via photosynthesis. The more plant biomass grown, the more carbon is removed from the atmosphere and oxygen is released.

Photosynthesis occurs for about three months on the Prairies and six months in wetter areas.

“We are really removing CO2 from the atmosphere three to six months of the year. The rest of the time, the ecosystem is sleeping,” Bork said.

Grasslands cover about a quarter of the land base and store up to 30 percent of the world’s soil carbon.

About 300 gigatonnes of carbon are stored in the temperate grasslands of Western Canada, South America and central and northern China.

His research team worked on 100 sites across the Alberta and Saskatchewan to see how much carbon they store based on tonnes per hectare.

“Even our most arid environment of dry mixed grass of southeastern Alberta around Medicine Hat store roughly seven tonnes per hectare of carbon. That is not a full accounting because we are not looking even deeper below 30 cm,” he said.

The wettest grasslands of southwestern Alberta store as much as 180 tonnes of carbon per hectare (72.9 tonnes per acre).

“Our wet grasslands are comparable to the boreal forest, which is shocking when I tell people that. Most people think forests hold more carbon — not true,” he said.

When a prairie soil is cultivated, a third to half of the carbon is lost to erosion or the furnace effect.

When a soil with lots of humus is cultivated, the insulation is lost. The surface is exposed to more sun and oxygen. Oxygenated soil allows the microbes to break down the carbon and release it.

Land-use conversion worldwide is contributing to rising CO2 levels in the atmosphere.

Long-term plots at Stavely, Alta., south of Calgary showed 30 percent of the carbon disappeared from the soil after three years of cultivation.

Perennial forages are preferred over other crops to restore carbon. Tame forages are also bred to produce more above ground to feed cattle but they do not put enough carbon back into the soil.

Annual crops are bred to produce everything on the surface and put very little below ground and do not have vast root systems. They are not adding carbon back into the deep soil profile.

Some of Bork’s work focuses on refining grazing to enhance soil carbon and provide an incentive to producers to increase soil carbon.

There is no clear consensus on the value of managed grazing but his analysis showed benefits where the presence of grazing animals tended to boost and maintain soil carbon.

“With this overall grazing effect, we were very pleased to find with long-term exposure to grazing we found an increase of soil carbon of 12 percent,” he said.

Most was concentrated in the top 15 cm of soil.

These soil carbon increases were not uniform everywhere. The dry, mixed grasslands did not show much change but the other regions did.

Further research is asking why these changes are happening. It is not known for sure if cattle change soil microbes or enzyme activity in the soil. Other studies are looking at litter turnover and rates of decay. Grazed areas have more rapid litter decay and cattle may help incorporate it back into the soil with trampling.

Other work is examining plant species.

They found introduced plant species like timothy, brome, bluegrass and dandelion actually increased soil carbon. This causes a conflict among the grazing purists.

“I am going to argue they are good. Many of them are very high in forage quality,” he said.

Another data set from nine former Prairie Farm Rehabilitation Administration pastures in Saskatchewan showed stocking rates have an effect on carbon sequestration.

“As you increase stocking rate, carbon increases,” he said.

Another unexpected result was the introduction of new plants.

Kentucky bluegrass litter decomposes rapidly and may contribute to carbon storage.

“Kentucky bluegrass appears to be adding something to these plant communities and it is introduced primarily through the presence of ongoing grazing,” he said.

A $2 million project is looking at the effect of adaptive multi-paddock grazing. This is intensive grazing in a large area, divided into small paddocks with quick rotations. There is a long recovery period to restore the leaves and rebuild roots.

Sites in Alberta, Saskatchewan and Manitoba are being studied for plant communities, carbon sequestration and biodiversity.

Bork argues carbon losses and gains have a measurable value.

Carbon in Alberta is priced at $30 per tonne based on the tax imposed on industrial emitters when they are above a certain threshold of CO2 equivalents.

He estimates carbon retained in the existing grasslands is worth about $9 billion based on the $30 tonne equivalent.

“When you look at the carbon already lost because of what we have done to our landscapes, these numbers are staggering. The area of land in the Parkland that has been converted, and attach that $30 per tonne CO2 equivalent, the amount is almost $23 billion. That is the value of the carbon that has been lost in the soils in the parkland region by converting them in the past,” he said.

About the author

explore

Stories from our other publications