Grassland management holds key to carbon capture, gas reductions

Planting perennial forages and improving soil organic matter are good management practices for cattle producers but they also offer the added benefit of sequestering carbon, says a federal researcher.

Alan Iwaasa, grazing management scientist at the Agriculture Canada Research and Development Centre in Swift Current, Sask., said producers are looking for ways to reduce their carbon footprint in light of increasing em-phasis on climate change, carbon tax and greenhouse gas emission reduction.

“We have a wonderful opportunity here with our soils,” he told the Saskatchewan Beef Industry Conference.

Soils that are in poorer condition can still build organic matter. There are about 14 million acres in the brown soil zone across Western Canada; about 10 million acres are in Saskatchewan.

The province also has 5.5 million acres in the semi-arid brown soil zone, or very dry land.

“Even traditional crop lands that are in environmentally marginal areas do have potential that we could convert those to perennial forages,” Iwaasa said.

Natural grasslands have been depleted since modern agriculture began. Only about 28 million of the original 151 million acres remain, he said.

The potential to sequester carbon in grasslands could be a huge advantage for Saskatchewan producers looking to offset emissions.

“Uncultivated grasslands of Western Canada contain two to three billion tonnes of carbon to the depth of one metre,” he said.

The associated ecosystem benefits of increased water holding capacity, improved soil structure and quality, nutrient cycling and reduced soil erosion are all advantages to cattle producers.

“In many cases you’re doing that already because you want to in-crease your production, you want to have healthier pastures, you want to improve your biodiversity,” he said.

Ways to improve or enhance carbon sequestration include different grazing management practices.

These can help the physical break down and compaction of vegetation, increase decomposition and soil incorporation and therefore restore degraded soils, he said.

“The challenge though is that in a lot of cases grazing systems’ intensity and frequencies may impact carbon storage but the effects are often difficult to measure and often are inconsistent due to the environment.”

Drought, flood and weather all affect carbon storage.

“These treatments need to be utilized consistently and over a long time to actually see the benefits, not just three or four years but sometimes for decades,” he said.

A paper published in 2014 examined the impact of agriculture and loss of bison on grasslands from 1927 to 2007 and the potential to sequester carbon even on land disturbed years ago.

“They found that grazing natural grasslands function still as a net carbon sink due to improved grazing management,” he said. “However, there is only a finite amount of soil organic carbon that you can put into these soils.”

Most of the brown soil zone contains only three to four percent carbon. The study found that net sequestration for the black, brown and dark brown soil zones were .09, .06 and .04 tonnes of carbon per acre per year, respectively.

Iwaasa said adding nitrogen-fixing legumes or nitrogen fertilizer to existing pastures or grasslands will boost sequestration.

The study found sequestration in the black soil zone of between .16 and 3.8 tonnes of carbon per acre per year.

Counteracting that will be the emissions from the fertilizer.

Interseeding legumes offers the advantages of increasing total soil nitrogen and above ground production, while storing .26 to .13 tonnes of carbon per acre per year.

Converting degraded land or marginal land that is annually cropped can store carbon but can take up to 150 years to return to its original state, Iwaasa said.

The study found net carbon gains of between .8 and 6.1 tonnes per acre in the brown to light brown zones, and between 8.1 and 26.7 tonnes in the black soil zone.

“Overall soil organic carbon gain is really dependent upon what you start with,” Iwaasa said.

So, a land base that is more de-graded offers more opportunity to build organic matter. Soil in better condition will build a minimal amount.

Another long-term study at Swift Current looked at reseeding native species on land that had been annually cropped since 1920.

It was seeded to two different mixes, a simple system with seven species and a complex system with 12 species, in 2001. Carbon measurements were taken in 2000, 2004, 2008, 2011 and 2014, and will again be taken this year.

Non-grazing, continuous grazing and rotational grazing systems were used with typical stocking rates.

“After the first four years we saw very good carbon sequestration potential occurring,” Iwaasa said.

At .31 tonnes per acre per year, he described that as “phenomenal.”

It had been dry from 2001 to 2004 and the native species established well.

There were no differences associated with the various grazing treatments as far as carbon storage levels up to 2014.

But there were differences over the years. In 2008 and 2011 the carbon levels declined and in some cases were even lower than when the study began.

In 2014, the carbon again in-creased and overall about .94 tonnes of carbon per acre per year has been stored.

“This is perplexing,” Iwaasa said, adding other factors are at play.

Possible reasons that grazing didn’t affect carbon levels are location, forage type and environmental conditions. There are few long-term studies with grazing and soil organic carbon, he said.

Reasons for losing soil organic carbon could be lack of or too much moisture. More, longer-term studies are needed, he said.

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