06.29.2021

Portage Farm Report: Carbon cycle and sequestration

By Shawn Cabak

Beef Cattle and the carbon cycle

Every living thing contains carbon, including cattle and grasslands and all are part of a carbon cycle. Carbon cycles vary around the world, by farm and depend on different management practices. Raising cattle can have both positive and negative impacts on the carbon cycle and different management practices can increase or decrease the sector’s carbon footprint.

Cattle emit greenhouse gases like enteric methane (CH4), a natural by-product of rumen fermentation. A management practice, such as including a feed additive like monensin, can help reduce enteric methane emissions while still enabling cattle to convert roughage into nutrient-rich beef. Burning fossil fuels for feeding or forage operations emit carbon dioxide (CO2). Producers can reduce carbon dioxide emissions by implementing extended grazing such as corn or bale grazing to reduce reliance on daily feeding.

Perennial forages and grasslands – the foundation of the beef cow-calf sector for grazing and winter feed– are an important part of the carbon cycle because of the sequestration process. Forages and grasslands capture carbon dioxide (CO2) during plant growth and sequester carbon in underground roots. Grasslands store up to 30% of the world’s organic carbon, and perennial grasslands are particularly effective carbon sinks, storing up to 97% of their carbon belowground.

Carbon sequestration on grasslands

Plants take in carbon dioxide (CO2) from the atmosphere during photosynthesis for plant growth, release oxygen into the atmosphere, and sequester carbon underground within their root systems. All plants, including trees, annuals, and native and tame perennial grasslands, sequester carbon, however not all carbon sinks are equal. In stable conditions, forests sequester more carbon in timber, leaves and needles, than grasslands can store above and below ground. However, when a forest fire occurs, much of this carbon is promptly released back to the atmosphere during combustion.

Annual crops sequester the least amount of carbon underground. Annual cropping systems are important for food and feed production, however compared to native grasslands, annual cropland often provides fewer ecosystem benefits, such as reduced biodiversity, reduced carbon storage and decreased soil water availability.

Scientists estimate that between 50 and 200 tonnes of carbon per hectare is stored in Canada’s grasslands, with an additional 3 to 12 tonnes of carbon per hectare stored in above-ground plant growth and plant litter. Most of the carbon sequestered is typically contained in the top 15cm of the soil. Soil organic carbon can also increase with grazing, particularly in the surface (0-15cm) soil, with minimal changes below this depth.

Historical land use change is the single largest disturbance of grassland carbon, leading to an estimated global loss of 30-50 percent of grassland carbon stores. Practices such as converting grassland to cropland, draining wetlands, and housing/highway construction, lead to carbon loss. Beneficial land use practices, such as revegetating annual cropland to perennial forage or using livestock manure as a fertilizer can help rebuild carbon stocks, but it is unknown whether the previous carbon stocks can be restored or how long it may take.

Management practices to increase carbon sequestration

Farms can implement management practises that promote removing carbon dioxide from the atmosphere (through plant growth) and sequestering that carbon belowground (in the root system and soil). There are some on-farm practices that producers can implement to increase sequestration and stability:

– Canadian studies have shown that moderate grazing can increase soil carbon concentration, particularly in the top 15cm of the soil surface. Grazing appears to be more beneficial for soil carbon in moister grasslands than in dry areas. Moderate grazing can also enhance other ecological services, including plant diversity and forage production.

– Native grassland plant species tend to have higher root-to-shoot ratios than tame forages and tend to have more root mass belowground than tame species. When revegetating annual cropland to perennial grassland, including native plant species may be an effective way to increase carbon storage.

– Left undisturbed, wetlands typically store more carbon than they release, resulting in net carbon sequestration. Wetland restoration can help re-establish ecological functions and result in a net carbon benefit.

There is a growing interest in trading carbon through credits or offsets. Pilot projects across Canada are being set up, including the Canada Grassland Project Protocol. Led by the Canadian Forage and Grasslands

Association, this project will help producers determine how much carbon they sequester in pastures and wetlands under different management practices. When carbon stores are better quantified on a farm level, farmers may be able to establish a value for the carbon they are sequestering and trade carbon offsets in the future.

Even though beef production in Canada produces greenhouse gases, this is offset by plants’ ability to store carbon in the soil. As technology and innovation allow producers to become more efficient at producing beef it will improve the understanding the role that grasslands and forages play in carbon sequestration.

This article appeared on The Graphic website at https://www.thegraphicleader.com/news/farm-news/portage-farm-report-carbon-cycle-and-sequestration

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