Agricultural Carbon Sequestration
We are experiencing anthropogenic climate change. Our industrial and agricultural practices, specifically those involved in the creation and release of greenhouse gases (namely carbon dioxide, methane, and nitrous oxide), has resulted in global climate change. While the burning of fossil fuels such as coal, methane gas, and petroleum, is the most commonly discussed form of greenhouse gas (GHG) emissions, significant amounts of carbon dioxide and nitrous oxide have been emitted due to agricultural and land management practices.
In our fight against global climate change, the easiest and most readily available solutions typically come in the form of GHG emission reduction. That is to say, finding ways to produce and release fewer GHGs in our energy generation, transportation, manufacturing, etc. Unfortunately, if we seek to mitigate anthropogenic climate change to a degree in which our global climate and ecosystems can still recover, we need to do more than limit our GHG emissions. We need to actively remove GHGs, namely carbon dioxide, from the atmosphere.
This is where “Carbon Sequestration” comes in. This process is the recapturing of carbon dioxide from the atmosphere back into the earth (with “the earth” being plants, our soil, or our oceans). Our earth currently sequesters about 55% of the carbon we emit into it, but that still leaves 45% of a gargantuan amount of carbon dioxide to build up year after year. While efforts to sequester carbon from the atmosphere take many forms, including afforestation (the planting of trees where there previously wasn’t) and reforestation, wetland restoration, and even artificial carbon filtering, in this article we’ll be focusing on those related to agriculture. Agriculture is the one major sector of human development that has the potential to switch from a net emitter of GHGs to a net sequesterer. While our agricultural practices are responsible for significant GHG emissions, they also hold incredible promise in the realm of sequestration. In this article, we’ll discuss how agricultural carbon sequestration works, how it’s being implemented, why it’s an important part in our fight against anthropogenic global climate change, and what the future may hold for it.
How does it work
When rich natural land such as forests, grasslands, and woodlands are converted to agricultural lands, the organic carbon within the soil reduces significantly (by up to 40%) as a result of the removal of organic content. While the modification of land use from natural environments to agroecosystems can deplete the soil organic carbon levels, the deficit created over time presents an opportunity to sequester carbon through careful land management practices. Natural carbon sequestration happens through biological, chemical, and physical processes. In most agroecosystems, this happens either via photosynthesis, in which carbon dioxide is absorbed by plants and chemically altered before being stored in the soil, or by the natural degradation of organic material (which contains carbon) into the soil. In agricultural carbon sequestration (and any terrestrial carbon sequestration for that matter), soil carbon is the name of the game. While natural landscapes like forests and stable grasslands are considered prime terrestrial carbon sinks due to their stability and “permanence” in structure, agricultural soils still carry significant potential as carbon sinks and need to be heavily considered as such since our populations couldn’t survive if we converted them all back into forests and grasslands.
How is it implemented
A variety of practices have and can be implemented at scale in agricultural settings to address emissions and enact significant sequestration efforts. Some of these include non-tillage or conservation tillage, organic production, the reduction of soil inputs (fertilizers, pesticides), cover cropping, and crop rotations. In most cases, these practices work to drastically increase the amount of carbon stored in our soils by employing methods that involve ‘minimal disturbance’ of soil.
No-Till and Conservation Tillage
These methods work to grow and harvest crops in the residue of previous harvests, which have been left on the top soil to naturally degrade. Not only does this practice reintroduce carbon back into the soil, but the minimal disturbance of the soil itself mitigates processes that release carbon already stored within. All of this works to increase the soil’s capacity to absorb carbon, and stop any additional carbon from being released. As with many other sequestration enhancing practices, no-tillage and conservation tillage has the added benefit of improving soil quality, and reducing fuel and water consumption.
Planting cover crops on bare fields reduces the rate of soil erosion, allows it to absorb carbon far more rapidly, and allows it to retain far more water. The result of which is soil that not only sequesters far more carbon than it otherwise would, but also enriches soil health for future crops.
Responsible Land Use
Allowing for crop rotations and more sustainable grazing practices (such as rotational/seasonal grazing and the implementation of sustainable stocking rates) can increase levels of annual pasture biomass production and redistribute carbon throughout pastures, thus resulting in both the reintroduction of carbon into the soil, as well as an increase in the soils capacity to absorb atmospheric carbon.
Composting is a means of taking organic materials including both carbon and nitrogen, and locking it into soil (as opposed to allowing it to release into the atmosphere via other means of degradation). Additionally, this process offers the co-benefit of enriching soil quality and aiding in the growth of new crops tremendously.
Organic Systems
Many organic systems operate by utilizing composted animal manures and cover crops to improve soil quality naturally. As a result, carbon can be reintroduced and stabilized within the soil, and the improvement in soil quality can enhance its ability to absorb carbon from the atmosphere. Additionally, as an added benefit, synthetic fertilizers (which require vehicle emissions and create emissions of their own) are reduced.
Annual plants require cycles of tillage and seed planting to ensure adequate productivity year-round. Perennial plants on the other hand, can survive several seasons on their own and thus require less soil disturbance over time. Additionally, since they are planted for longer periods of time, their root structures are often larger and deeper, allowing carbon to penetrate further into the ground and consequently stay there longer.
Incentives
So, why would farmers go to the trouble of enacting these practices, practices that in many cases require more effort on their part, reduce productivity, and can be costly?
Subsidies and other Financial Programs
Many governments and companies incentivize carbon sequestration efforts by offering subsidies and/or credits proportional to the amount of carbon sequestered, and now more than ever, these financial incentives can be significant. A company called Nori has developed an incentive program that pays farmers based on the amount of carbon they sequester annually.
Soil Quality
Many of the practices involved in increasing the soil’s capacity to absorb carbon from the atmosphere are also incredibly beneficial to the health and quality of the soil itself. Practices like no-till or conservation till farming, crop rotations, cover cropping, and the use of compost, all work to make soil more nutrient dense, more structurally stable (or, erosion resistant), better able to retain water, and denser in organic matter. This is great news for farmers who know that healthy soil is the foundation for healthier and more productive crops.
Resource Conservation
As a result of increased soil quality and use of the organic matter left over by prior crops, agricultural fields that enact carbon sequestration practices often have higher quality soil and are able to retain more water. As a result, these fields can sometimes require less inputs of water and fertilizers, which not only reduces resource consumption from those buckets directly, but also reduces the power and vehicular emissions related to their application in the field.
Why it’s important
As previously mentioned, we simply will not meet our climate change mitigation goals if we do not increase efforts to actively remove GHGs from our atmosphere. While efforts are needed in every sector, it has been estimated that nearly 10% of global sequestration requirements (with respect to the amount needed to avoid the 2ºC warming-threshold) could be achieved via agricultural sequestration. This is a huge contribution to the overall goal, and must be included as a serious component of our plans moving forward.
While erratic weather patterns and rises in global sea levels are amongst the most commonly addressed impacts of climate change, there are many that impact our agricultural systems directly. Drought and intensified heat waves may seems like the main concerns, but the impacts can be far more nuanced when a global agricultural system is so finely tuned to our specific climate. A report from the USDA and the National Sustainable Agricultural Information Service list some of the following:
With increased carbon dioxide and higher temperatures, the life cycle of grain and oilseed crops will likely progress more rapidly.
The marketable yield of many horticultural crops, such as tomatoes, onions and fruits, is very likely to be more sensitive to climate change than grain and oilseed crops.
Climate change is likely to lead to a northern migration of weeds. Many weeds respond more positively to increasing carbon dioxide than most cash crops.
Disease pressure on crops and domestic animals will likely increase with earlier springs and warmer winters.
Projected increases in temperature and a lengthening of the growing season will likely extend forage production into late fall and early spring.
Climate change-induced shifts in plant species are already under way in rangelands. The establishment of perennial herbaceous species is reducing soil water availability early in the growing season.
Higher temperatures will very likely reduce livestock production during the summer season, but these losses will be partially offset by warmer temperatures during the winter season (Backlund et al., 2008).
The Future
Concerns
Many believe that many efforts to sequester carbon in these ways vastly overestimate the amount of carbon actually being removed from the atmosphere for a variety of reasons. Companies and research institutions around the world are working to improve both the research that informs carbon sequestration efforts, as well as tools to measure conditions and impacts on a case by case basis. Unfortunately, much of this science is still relatively young and many fear that efforts to fuel these practices may be more futile in nature than we wish to believe.
The benefits of many practices like no-tillage farming are explicitly dependent on the practice being sustained for the long term. The benefits offered by these practices can otherwise be quickly reversed if they’re abandoned in a short time frame. Many of the subsidies and other financial programs that incentivize farmers to take on carbon sequestration programs (while consequently reducing their agricultural outputs) fall victim to this pitfall when contracts or programs expire.
An unfortunate downside to some carbon farming operations is a reduction in agricultural productivity. This can often incentivize new farmland to crop up elsewhere. The result of this land use change, often from forests or grasslands, is that large amounts of sequestered carbon stored in those plants and soil are released in the turnover. Whats more, as an added consequence, this also speeds up the destruction and degradation of natural ecosystems.
Many sequestration efforts like no-tillage farming require pesticides/herbicides and GMO seeds to meet standards of productivity. While this isn’t inherently harmful, public concerns regarding pesticides and GMOs can make this path increasingly difficult for farmers to pursue.
Paths forward
Financial Incentives: Financial incentives, be it through private companies or government programs, seem to be the most powerful driving force propelling these efforts forward. Private companies are developing funds aimed toward paying farmers credits for their sequestration efforts, and many government programs are working to offer subsidies for the same. While the private sector is beginning to step up to the plate and help solve this problem, we need our governments to put more effort toward subsidizing sustainable agricultural practices rather than just large commodity-crop farming. This is how change happens.
Policy: Additionally, policies that include agricultural carbon sequestration in their climate-action plans are gaining significant traction. This is beginning to happen at all levels of government, and will likely be a significant player in our fight against global climate change.
Education: It’s critical that continued energy and resources be given to research regarding sequestration efforts, the co-benefits they may offer farmers, and the options available to consumers as we continue this fight. There are many farmers and agricultural experts who are sharing their deep passion for land stewardship with their peers to make important and necessary change.