No matter how hard we try, it is truly nature that will ultimately determine how much carbon can be sequestered in soil. The reality is that 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. 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
From the moment the very first plow broke ground, agricultural soils began losing carbon in the form of carbon dioxide (CO2). When the agricultural industry spanned smaller fields and used fewer inputs, this problem was not immediately visible. But carbon loss from soils is cumulative and has now reached unprecedented levels which are forcing us to come up with better solutions for sequestration or risk devastating consequences.
A recent Fact Sheet published by the American University of Washington, DC claims that "over the last 10,000 years, agriculture and land conversion have decreased soil carbon globally by 840 billion metric tons of carbon dioxide (GTCO2), and many cultivated soils have lost 50-70% of their original organic carbon". (1)
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 by the widely used 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 has weakened soil microorganisms, causing a decrease in soil organic matter (SOM). The weakened soil microorganisms combined with the loss of SOM have led to the inability of the 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 draw down 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
Knowing what we now know about this important topic, we have finally begun the imperative 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
While planting trees is an important step and can make us feel like we are doing right for our planet, with an erratic climate that includes prolonged droughts and wildfires, trees are also vulnerable. Trees store vast amounts of carbon in their trunks, limbs, and roots. In fact, 50% of the dry mass of a tree is carbon. That big oak in your front yard is sequestering a significant amount of carbon. Multiple studies have shown the older the tree, the greater its potential to store carbon, strengthening the 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. Most forests, especially old-growth forests, have established vibrant communities of microbes and fungi, making them capable of rebounding from a fire quite rapidly. Thankfully, fires do not kill the biology in the soil.
Although grass and range lands do not necessarily give us quite the feeling of joy we may get from a walk in the woods, they can be effective carbon sinks as well. Most of the carbon stored by grass is below ground. In semi-arid areas, grasses are also less prone to drought because they put down incredibly long roots in search of water. If a fire burns the grassland, most of the carbon remains in those long roots and in the 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". (2)
Forests may store more carbon than grasslands, but in an increasingly unstable climate, we really must consider both and treat them as carbon sinks. Efficient land management is essential and will determine how we can sequester carbon in the soil at the most optimal rates.
Root Biomass As A Primary Soil Carbon Sink
Whether you are looking at a wild prairie or a field of oats, those plants are working for you to sequester carbon both in their roots and in 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 effectively.
The carbon cycle is a closed loop with many necessary components. Plants use photosynthesis to fix atmospheric CO2 into their biomass and subsequently emit oxygen as result. Increased photosynthesis increases the amount of root mass. Plants form symbiotic relationships through their root exudates with the microbial life present in their rhizosphere. During this process, microbiology stores large quantities of nutrients, including carbon. Fungi stores large amounts of carbon in their 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.
Increasing plant root mass in your soil involves making sure the right biology is present, which efficiently cycles the nutrients needed for the roots to grow. Nutrient cycling serves two purposes: it increases the plant's capacity to sequester carbon in the soil and it improves soil health. Carbon-rich soil is healthy soil, and healthy soil leads to higher-yielding crops and more farm profit. Not to mention it also increases the nutritional value of our produce!
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 toward holistic growing practices that promote the building of biodiversity in the soil. With that, the fungal biomass will grow. Fungi are nature’s best-kept secret! They are natural carbon sequesters. With an increased presence of fungi, 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 its necessary components and how to best allow them to perform for optimal results. 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 that allows for nutrient cycling. Microbes need an abundance of SOM for a balanced diet. These are all necessary factors that lead to healthy soil.
Studies have shown that one way to increase soil health is by adding compost to cover cropped fields, which provides vital nutrients for microbes to function effectively. Compost supplies vital nutrients, though its specific composition is dependent on where it is derived from. Adding Humic Land™ to your compost can help to maintain a balance in necessary nutrients, as it contains both humic and fulvic acids, ensuring that your soil, plants, and microbes all perform at an optimum level.
Soil Disturbance
Plowing, tilling, and many other agricultural practices that disrupt the soil can destroy its ability to sequester carbon. These actions can strip the fungal biomass necessary for healthy soils, releasing increased amounts of CO2 into the atmosphere. Regenerative agriculture’s holistic approach to farming focuses on increasing carbon sequestration in the soil.
More farmers and growers are planting cover crops to minimize areas left bare 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 only but a few times when one single activity results in multiple benefits; 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 draw down the atmospheric greenhouse gases into the soil. Improving Soil Health increases soil's ability to sequester carbon but also creates a healthier environment for healthy plants and trees. All of these create a healthier planet able to sustain healthier humans!
Sources
1. https://www.american.edu/sis/centers/carbon-removal/fact-sheet-soil-carbon-sequestration.cfm
2. https://www.courthousenews.com/scientists-find-grasslands-important-as-carbon-sinks
