Where Does Carbon Go?
By Hillary Luchinski, AAg, Agri-Environmental Specialist, Humboldt
Carbon emissions play an important role in climate change. Agriculture has the potential to help store enough carbon in soils and wetlands to remove a significant amount from the atmosphere and combat climate change.
Agriculture and Agri-Food Canada (AAFC) reports that in 2016, Canadian soils removed 11.2 million tonnes of CO2 from the atmosphere. According to AAFC’s Soil Organic Carbon Change Indicator, Saskatchewan has some of the highest rates of carbon sequestration in the country. That same indicator shows that most Saskatchewan soils have stored more than 1,200 kg/ha of soil organic matter (SOM) between 1981 and 2016, as a result of land management changes in tillage and summerfallow.
So how do we store carbon in our soils? We capture carbon by building SOM, which also plays an important role in feeding our soil microbial and fungal community, for soil aggregation and water infiltration, absorption and retention.
It is important to note that not all organic matter is created equal. There are three fractions of organic matter—dissolved organic matter (DOM), particulate organic matter (POM) and mineral-associated organic matter (MAOM). POM (the largest SOM fraction) is the easiest fraction to build, since it is built primarily through the breakdowns of root biomass, but the challenge is that it also cycles quickly, sometimes as fast as one to 10 years. Meanwhile, MAOM (associated with the mineral or clay component of your soils) is formed by soil microbial processes and is thus tied up in the soil for longer. MAOM is smaller, harder to build and has a saturation point, limited by the clay content in your soils. DOM is very small and extremely mobile, moving throughout the soil profile via soil water content.
Anyone can get their soils tested to see what percent of their organic matter is mineral-associated versus particulate, as the two fractions can be separated by weight and size. Measuring the carbon within each is a bit more complex but is still possible and is an important consideration for the future of managing lands specifically related to storing carbon.
Land management practices are not the only factor impacting carbon sequestration; soil characteristics such as clay content are just as important and much more complex. Because of this and the fact that MAOM has a unique saturation point based on the clay content of the soil, each farming operation is unique in terms of how much carbon can be sequestered and how long that carbon is tied up in the soil. For example, producers on soils that have a low clay content, such as sandy soils, can consider focusing on building POM through minimizing soil disturbance, focusing on belowground biomass and considering adding biochar to their soils to act as a nucleus for soil aggregation.
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