Today, existing methods of carbon sequestration are insufficient to offset accelerated emissions.
Carbon sequestration is the process of capturing, securing and storing atmospheric carbon dioxide in a stable state. This process can help reduce the human carbon footprint, therefore helping balance the uptake and the offset of carbon. There are two main types of carbon sequestration: biological and geological.
In the following section, we take a closer look at biological processes that occur in soil, forests and other ecosystems that can store CO2, which are sometimes called “carbon sinks.”
Soil carbon sequestration
Soil is an enormous carbon sink. However, tillage, chemical fertilizers and other common agricultural practices can drastically reduce the amount of organic carbon in the soil.
There are several practices that can help pull carbon out of the atmosphere and put it back into the soil, where it can contribute to soil health, crop yields, water storage and other beneficial functions.
Follow the links below to learn more about each of these practices:
- Regenerative agriculture
- Managed grazing
- Plant nutrient management
- Regenerative annual cropping
- Perennial crops
Agroforestry can be defined in simple terms as “agriculture with trees.” It is a farming system that combines trees and/or shrubs with crops and/or livestock. It has multiple environmental benefits, including carbon sequestration. It also provides multiple revenue streams and job opportunities for farmers that may help to protect the growing trees while supporting local economies.
a. Multistrata agroforestry
This system simulates the structure of a forest by blending an overstory of tall trees with an understory of layers of crops. It can sequester similar amounts of carbon per acre as planting new forests or forest restoration projects. Additionally, it produces food and therefore generates income very quickly for the farmers.
There are many other benefits of this system as well. Agroforestry plots can reduce pressure to cut forests in order to grow crops. The trees prevent erosion and flooding and help stabilize the soil on steep slopes that may otherwise be unsuitable for crops. The system also produces firewood, which further reduces pressure on nearby forests.
b. Tree intercropping
Tree intercropping refers to growing trees together with crops, a form of agroforestry that has been widely adopted by tropical smallholders.
Tree intercropping helps increase the carbon content of the soil and productivity of the land. The placement of trees and crops can vary according to climate, topography, crops and other variations. Examples include alley cropping, which involves alternating rows of trees or hedges and crops, while parkland systems include scattered trees or clumps of trees throughout the land.
This farming system fell out of favor as farming was mechanized, but it can provide many benefits that warrant a second look. In addition to reducing erosion, the trees provide windbreaks and habitats for birds and pollinators, and they also provide shade for light-sensitive crops.
Biochar is a black carbon produced by heating biomass sources (e.g., wood, wood chips, sawdust, yard waste, crop waste, food waste, and even manure or sewage waste) at high temperatures in the absence of oxygen in a controlled process called pyrolysis. All materials are burned, and all volatile gases are removed, releasing little to no contaminating fumes. The resulting product is a crystalized carbon skeleton of biomass.
The end product, biochar, is black, very porous, lightweight and has a large surface area. About 70% of its composition is carbon, and the remaining elements include nitrogen, hydrogen and oxygen, among others. It has a negative charge and holds nutrients like calcium, potassium and magnesium. Additionally, it won’t biodegrade and can last hundreds or thousands of years in the soil.
What are biochar’s applications in agriculture?
For soil amendment, due to its high porosity, large surface area and negative charge, biochar acts like little sponges that help retain more water in the soil, which helps reduce runoff and erosion during times of drought. It also increases the soil biological activity, as the pores in biochar make a perfect habitat for microbes, acting like coral reefs for soil microbes.
Due to its negative charge, biochar can hold onto positively charged ions like calcium, potassium and magnesium, preventing nutrient leaching and reducing the amount of fertilizer needed. This can help improve crop yields and can reduce the use of chemical fertilizers, which are expensive and have higher carbon footprints. Biochar can also be added to manure or compost.
In manure management, through the process of pyrolysis, manure solids can be converted into biochar, helping farms reduce the volume of manure by 75% to 95%, and turning this waste product into a useful byproduct. It can then be used in lagoons, where liquid manure is being stored, to reduce odors, as it absorbs ammonia, hydrogen sulfide and methane. It retains the nitrogen that would otherwise be lost as ammonia, so the manure turns into a richer fertilizer.
Biochar can also be added to cow bedding to help reduce odors, keep stalls dryer and therefore improve hoof health and overall cow health. Because of its porosity and ability to hold ions, it can reduce water pollution, and around silage storage or compost piles, it can be used to absorb nutrient runoff. Overall, biochar can help improve water quality as it can immobilize toxic metals, stabilize nutrients, filter runoffs, reduce groundwater contamination and decrease eutrophication of streams and lakes. In aquaculture, biochar can be used to treat and filter water.
Most biomass decomposes and returns to the atmosphere eventually. When biochar is made, it pulls some of that carbon out of the cycle and sequesters it, so it does not return to the atmosphere. Biomass can decompose into methane or CO2 and can be incinerated to produce CO2.
The climate benefits of adding biochar to soil include carbon sequestration; reduced methane reductions from manure, compost and soils; decreased nitrous oxide emissions from soils; and it can be a source of renewable energy.
Biochar can make cropland more resilient to weather extremes from climate change, as it improves water holding capacity, soil porosity and water filtration.
Regarding the use of biochar in feed additives, there is still debate on whether biochar may improve health and reduce emissions — more research needs to be conducted. It is approved in Europe, Australia, Canada and Japan; however, it has not been approved in the United States of America by the U.S. Food and Drug Administration (FDA). "
Silvopasture, which is a kind of agroforestry, is regenerative agriculture that farms livestock and trees together. For example, a farm might produce cattle alongside soybeans and trees in a symbiotic system. Benefits include:
- The livestock and trees work together to sequester carbon in the trunks, branches and roots of the trees as well as in soil carbon.
- Trees can increase animal welfare by helping protect livestock from extreme weather, such as wind and heat.
- Trees also provide forage for livestock to eat.
- The shelter and improved nutrition from these trees increase animal health as well as the production of meat, milk and offspring. In fact, some research has shown that dairy cows can improve their milk production simply by being in the shade.
- Livestock such as cattle provide natural weed control and fertilizer.
- Farmers reap the financial rewards from this decrease in inputs.
- The trees also provide a more diversified income by producing fruits, nuts or lumber, shielding farmers from financial risk.
Meet Daniel Wolf, who has been implementing silvopasture with his family on their farms in Brazil for more than 10 years.
According to Drawdown, if adoption expands to 720–772 million hectares by 2050 — out of the 823 million hectares theoretically suitable for silvopasture — carbon dioxide emissions can be reduced by 26.6–42.3 gigatons. This reduction is a result of the high annual carbon sequestration rate of 2.74 tons of carbon per hectare per year in soil and biomass. Farmers could realize financial gains from revenue diversification of US$1.7–2.3 trillion, on investment of US$206–273 billion and lifetime operational cost of US$2–3 trillion to implement.