No matter how hard we try nature will determine how much carbon can be sequestered in soil. Not all soils are created equal. Soil Organic Matter (SOM) is the basis for carbon sequestration. The higher the SOM the more carbon can be sequestered in the soil. Climate, farming practices, and topography play major roles in creating fertile soil that can sequester the maximum amount of carbon.
Actual Carbon Sequestration in Agricultural Soils
When the first plow broke ground, agricultural soils started losing carbon in the form of carbon dioxide (CO2). When fields were smaller and agricultural implements less effective this didn’t seem to be a problem. But carbon loss from soils is cumulative. In a fact sheet published by the American University in Washington, D.C.
This loss of carbon is the result of a combination of factors. Fewer plant roots and residues have been returned to the soil as native prairies and forests have been converted to agricultural land. Increased tillage, especially the moldboard plow, has brought carbon-rich soil to the surface, where the carbon oxidizes and enters the atmosphere as carbon dioxide.
The use of nitrogen fertilizers and toxic chemicals have weakened soil microorganisms, causing a decrease in soil organic matter (SOM). The weakened soil microorganisms combined with the loss of SOM has led to the inability for soil to sequester carbon and an increase of carbon dioxide in the atmosphere. The USDA estimates that over 24 % of total carbon dioxide emissions are from agriculture.
But there is potential for soils to drawdown carbon from the atmosphere with changes in farming practices. On average, soil holds 3 times the amount of carbon in the atmosphere or almost 4 times the amount held in living matter. We just have to live and farm smarter on our planet.
Ways to Get Carbon Back Into our Soils
We have begun the task of sequestering carbon in our soils. First adopter farmers are changing their crop management practices to increase carbon in their field soils. Forest management and additional trees in urban areas, as well as converting agricultural land to forests (afforestation), have all added up to an 11.6% increase in soil carbon sequestration, according to the EPA.
Many factors affect the potential for drawing down atmospheric CO2 into soils as carbon. Climate, historic land use, current crop management strategies, and topography all play a part in the success of carbon sequestration.
Trees and Grasslands
Planting trees makes us feel like we are doing great things for our planet. We are. But with an erratic climate that includes prolonged droughts and wildfires, trees are vulnerable. Trees store vast amounts of carbon in their trunks, limbs, and roots. 50% of the dry mass of a tree is carbon, that big oak in your front yard is sequestering quite a bit of carbon. Multiple studies have shown the older the tree, the greater its potential to store carbon. There is a strong argument for retaining our Old Growth Forests.
When a fire rips through a forest all the aboveground carbon is converted into carbon dioxide and escapes into the atmosphere. But because forests, especially old-growth forests, have established vibrant communities of microbes, especially fungi, a well-managed forest can rebound from a fire quite rapidly. Fires don’t kill the biology in the soil. Trees are beautiful, hold large amounts of carbon, and give us joy to look at.
Grass and range lands don’t give us quite the feeling of joy from a walk in the woods, but grass and range lands can be effective carbon sinks as well. Most of the carbon stored by grasses is belowground. In semi-arid areas grasses are also less prone to drought, they put down incredibly long roots in search of water. If a fire burns the grassland, most of the carbon remains in roots and soil.
“In a stable climate, trees store more carbon than grasslands,” says Benjamin Houlton, director of the John Muir Institute of the Environment at UC Davis. “But in a vulnerable, warming, drought-likely future, we could lose some of the most productive carbon sinks on the planet. California is on the frontlines of the extreme weather changes that are beginning to occur all over the world.”
Forests store more carbon than grasslands. But in an increasingly unstable climate, we should look not just at our forests but also the grass and range lands as carbon sinks. Land management will determine if we can sequester carbon in the soil at optimum rates.
Root Biomass as a Primary Soil Carbon Sink
Whether you are looking at a wild prairie or a field of oats, the roots of all those plants are working for you to sequester carbon both in their roots and the soil around them. Soil Organic Carbon (SOC) is a fraction of the SOM. Without a high % of SOM your soil will be unable to sequester carbon.
The carbon cycle is a closed-loop with many components that are necessary for that loop. Plants use photosynthesis to fix atmospheric CO2 into their biomass, emitting oxygen. Increased photosynthesis increases the amount of root mass. Plants form symbiotic relationships through their root exudates with the microbial life present in its rhizosphere. During this process, the microbiology stores large quantities of nutrients, including carbon. Fungi stores large amounts of carbon in its mycelium in the form of oxalates on the exterior of their hyphae. Humus is a “by product” of the process and contains stabilized forms of carbon.
The way to get a large root mass in your soil is to make sure the right biology is present to efficiently cycle the nutrients needed for the roots to grow. This serves two purposes; it increases the plant capacity to sequester carbon in the soil and improves soil health. Carbon-rich soil is healthy soil. Healthy soil gives you higher-yielding crops and more farm profit. Healthy soil also gives you nutritious food.
The Microbial Community
The impact of the biodiversity available in the soil can not be more stressed than in this case. Historical growing practices have led agricultural “dirt” to reach very high levels of bacterial biomass. Unfortunately, bacteria are not the greatest carbon sequesters. Bacteria have much higher levels of Nitrogen compared to their capacity to retain carbon.
Emphasis must be directed towards holistic growing practices that promote the building of biodiversity in the soil. With that, the fungal biomass will grow. Fungi is nature’s best-kept secret! They are natural carbon sequesters. With fungi increased presences, agricultural soils capacity to hold SOC increases by multiple folds.
Feeding the Soil
For a perfect closed-loop carbon cycle, we have to consider all the necessary components and how to allow them to perform at their best. For plants to photosynthesize CO2 out of the atmosphere, they need to be healthy. They need fertile soil and the proper amount of water. For plants to create healthy root mass, they need porous soil. Microbes need SOM for a balanced diet. All these parts revolve around healthy soil. Studies at UC Davis have shown adding compost to cover cropped fields added vital nutrients for microbes to function effectively.
Compost supplies many nutrients, and which ones are dependent on where the compost is derived. But wherever they come from on the farm, they represent an opportunity for multiple interconnected benefits. Humic Land added to your compost supplies missing nutrients, as well as humic and fulvic acids, so your soil, plants, and microbes perform at an optimum level.
Plowing, tilling, and any type of agricultural practice that disrupts the soil destroys the soils ability to sequester carbon. The action of plowing and tilling shops all the fungal biomass important for healthy soils, releasing increased amounts of CO2 into the atmosphere. Regenerative agriculture’s holistic approach to farming indirectly focuses on increasing carbon sequestration in your farm soil.
More farmers and growers are planting cover crops to minimize areas left bared but also to offer a constant source of organic matter available for the diverse biology to feed on. Their use leads to better water retention on sandy soils, helps break up clay soils, and stops erosion. These all add up to increased carbon in your soil.
Healthier Soils Sequester Higher Levels of Carbon
There are few times when one activity results in multiple benefits. But carbon sequestration in your soils is one such time. Until our sun quits shining, we will have a source of energy for photosynthesis. If we consider ALL the players in the carbon cycle as equal and necessary, slowly, we will be able to drawdown the atmospheric greenhouse gases into the soil. Improving Soil Health increases soil ability to sequester carbon but also creates a healthier environment for healthy plants and trees. All of which create a healthier planet and a healthier you!
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