Soil Carbon Isn’t The Answer. Focus on fossil fuels, land use, and methane instead.
As transport electrification continues, and charging stations like this replace conventional gasoline fueling stations, the need for gasoline additives, like ethanol, will decline, freeing up the early 40 million acres of American cropland currently dedicated to corn for ethanol production.
Soil carbon, especially carbon in agricultural soils, isn’t going to save us.
It isn’t even a big enough climate wedge to get the agri-food sector to reach within-sector climate targets set by The Intergovernmental Panel on Climate Change (IPCC) IPCC, let alone serve as mitigation for other sector’s emissions.
Yet, soil carbon keeps sucking up all the metaphorical oxygen in the corporate climate space. Why is this? And if not soil carbon, what are some other climate wedges that deserve more airtime from corporate agrifood actors?
Agriculture has a critical role to play addressing climate change and adapting to unavoidable climate change already underway. When corporate sustainability staff and conferences oriented towards this audience discuss the biggest climate issues in agriculture today, soil carbon continues to dominate the conversation. In reality, it’s just a piece of the puzzle, with a relatively minor role to play in mitigation (AKA removals). Soil carbon, and the management practices that encourage its accumulation, like cover cropping, intensified crop rotations, perennial crops, and amendment with organic matter sources like manure and compost, will definitely have an increasingly important role to play in making agriculture more resilient to the extreme heat and precipitation brought by climate change. However, these very same issues, especially the heat, will also increase the rate at which soils lose carbon, making the net climate value of this carbon marginal and increasingly risky over the next century.
But, there are other important climate contributions for the agrifood system. Excessive focus on soil carbon limits our collective imagination and energy for more promising paths.
Shifting focus to land use, eliminating fossil fuel use, and greenhouse gas-specific strategies are all more promising avenues.
Tile-drained soils have poor prospects for soil carbon sequestration
Soil carbon sequestration efforts are highly context-dependent. The effectiveness of increasing photosynthesis or reducing soil respiration to manipulate the soil carbon pool depends on historical baseline conditions, management practices, and soil types. In regions with limited native photosynthesis and clay-rich soils, like deserts, implementing irrigation and certain cropping systems might lead to higher rates of photosynthesis, carbon inputs, and soil carbon.
However, those are not the attributes of most of America’s cropland. Rather, our cropland was mostly historically grasslands (or forests), which were drained, increasing soil respiration and liberating carbon stored over thousands of years. Attempts to boost photosynthesis in these systems with inputs contribute to higher fossil carbon greenhouse gas emissions from natural gas combustion used to produce nitrogen fertilizer. These high fertilizer, high yield systems also have high nitrous oxide emissions, the greenhouse gas that constitutes about a third of the sector’s climate impact (the other thirds are methane emissions from ruminants and manure, and carbon dioxide from conversion of forests and grasslands to cropland).
There’s decent coverage of land use change in Brazil, but less discussion of domestic shifts. Most of America’s soils have experienced relatively recent land use change, such as the installation of tile drainage systems, to convert wetland soils into cropland to support expansion of corn and soy production, particularly in the upper midwest. Water inhibits carbon loss, but drainage speeds up soil carbon loss, especially at depth by bringing oxygen down to the microbes that convert organic matter to carbon dioxide. Between 2012 and 2017, more than 7 million acres – concentrated in the Corn Belt and Great Lakes states – had new tile installed, which is a 14% increase. This trend has continued, converting former riparian or wetland soils to cropland. These soils will likely continue to lose carbon, even if “climate smart” annual cropping practices are implemented. These acres are not a smart investment as they are unlikely to deliver any climate returns.
A land use play that needs more air time: Let’s abandon ethanol
So much focus on soil carbon or specific field’s greenhouse gas performance steals focus from systemic land use considerations. Corn ethanol, a fuel that should ideally disappear with transport electrification over the next decade takes up 40 million acres of American cropland. That’s more than 20 times the number of acres dedicated to vegetables in total in the US. In fact, it’s more acres than are dedicated to cultivating fruits, nuts, melons, vegetables, rice, peanuts, beans, lentils, and chickpeas by a factor of 4. Deflating corn ethanol demand would alleviate this burden and facilitate the transition of surplus agricultural land back to forests or prairies, while still leaving plenty of space for growing food crops, even if we expanded food crop production a few times over.
Fossil fuels need to go - focus on fossil methane first
The IPCC is crystal clear: fossil fuel emissions need to be reduced 50% by 2030 and virtually eliminated by 2050. This means all the diesel, propane, and natural gas embedded in both agricultural production and supply chains needs to go. . This decade, scientists urge a focus on methane emissions , and other short-lived more potent industrial emissions like refrigerants. Since fertilizer production relies on natural gas, efforts to shift at least some nitrogen provisioning to biological nitrogen fixation with legume cover crops is a great way to do this high value decarbonization. Similarly, the R&D and and capital investments to electrify production and transport holds substantial potential to reduce emissions and needs to happen now. This shift could yield greater emissions reductions than estimated soil carbon sequestration and provide long-term benefits consistent with the IPCC pathways.
Climate smart focal shifts
While soil carbon sequestration remains an important strategy within agriculture to adapt to unavoidable climate change, we must avoid excessive focus on this single strategy. It is essential to recognize that it is not the panacea we often perceive it to be.
Recognizing the limitations of soil carbon and shifting energy to other critical issues, such as land use, fossil fuel elimination, and high impact gasses like methane and refrigerants, we can develop a more comprehensive and effective approach to a climate smart agrifood sector.
It is imperative that we prioritize research, collaboration, and material (not marginal) solutions to drive IPCC-aligned change in the agri-foodsector, ultimately contributing to a more sustainable future not just for the sector, but for all of us.
