Centuries of unsustainable agriculture have squeezed massive amounts of nitrogen and carbon out of soils, and Ohio State’s Rattan Lal, a professor of soil science who has presciently spoken out about restoring forests and soils for carbon mitigation and sequestration, says we can pull about 10 percent of our greenhouse gasses out of the air and inject them into soils just by switching to climate-safe agriculture – a practice that could also increase farmers’ yields and save on fertilizer costs.
“Soil,” which better than “dirt” connotes the rich biodiversity and dynamic chemistry it houses, is finally getting the attention it deserves, both in mainstream media like the New York Times and in global climate talks, as the costs and benefits come more clearly into focus.
One reason for the renewed attention is the French government’s “4 per 1000” initiative, which is a voluntary effort to increase carbon in soils by four parts per 1000 of soil annually, or a 0.4 percent annual increase of soil carbon, globally. Essentially, 4 per 1000 strategizes soils as a carbon sequestration front, with soils holding on to carbon that would otherwise reside in the atmosphere. While the 4 per 1000 website offers varied and nuanced information, it does offer a bold main thrust of the program: “An annual growth rate of 0.4% in the soil carbon stocks…would halt the increase in the CO2 (carbon dioxide) concentration in the atmosphere related to human activities.”
This high ambition has engendered a push-back from quite a few soil scientists who believe that 4 per 1000, however auspicious, might be over-promising soil as a climate change mitigation and sequestration measure. These soils scientists welcome global efforts to improve soil quality – and increased carbon content is central to bettering soils health – but they aver that sustaining the .4 percent increase over many years is too high in terms of soil ecology. They also point out that there are real economic challenges that need to be considered if soils are to emerge as an important climate mitigation and sequestration strategy as well as a promising global focus for sustainable agriculture.
Nonetheless, soils, which fall within the advisory Intergovernmental Panel on Climate Change’s (IPCC) “Land use, Land-Use change, and Forestry” (LULUCF) category, can eventually become a cost-effective contribution to the Paris Accords goal of limiting global temperature rise to 1.5- 2.0 Centigrade degree increase relative to pre-industrial levels, even if not at the 4 per 1000 level.
Natural resource economist Dominic Moran, who is on the faculty at Scotland’s Rural College (SRUC), has worked on the economics of climate mitigation for years, and he sees both hurdles and promise for large scale soils carbon sequestration. He points out LULUCF accounts for approximately twenty-five percent of global ghg emissions and there is no reasonable way to achieve the Paris Accord goal without addressing LULUCF. And, Moran says, carbon sequestration in soils is a promising LULUCF mechanism – even as a negative emissions technology, by which atmospheric carbon is pulled down into the Earth. “Because there is a lot of soil in the world and a lot of it can be improved, there is a lot of abatement potential,” says Moran.
This points to the role natural resource economists will play to make soils sequestration viable at a large scale. In the meantime, soil ecologists are offering central economic as well as ecological considerations, which natural resource economists can follow and provide fuller guidance.
Soil Ecologists Posing the Economic Questions
Agricultural ecologist David Powlson, with the famed Rothamsted Research, at Harpenden UK, considered the seminal large field agricultural research center, is one agroecologist who has caveats as to four per thousand goal for soil. Powlson co-authored the January 2018 Global Change Biology paper, “Major Limitations to achieving ‘4 per 1000’ increases in soil organic carbon stock in temperate regions: Evidence from long-term experiments in Rothamsted Research, United Kingdom.”
For the Global Change Biology paper, Powlson and co-investigators looked at a unique data set of soil samples going back over 150 years that are connected with Rothamsted experiments that varied soil management. For example, one Rothamsted experiment rotated crops with eight years of grass and clover covering the fields followed by two years of arable crops. Soil organic carbon matter, Powlson explains, “changes generally quite slowly in response to change of management, and so these long-term experiments are valuable for looking at what a certain change in management will do for soil carbon content.”
Powlson says an impetus of his Global Change Biology paper was that he and other soil scientists were concerned about hopes raised by the 4 per 1000 mil initiative. So Powlson and colleagues looked at their long-term experiments to assess the carbon soil increase rate in connection to land management. They found that in general soil carbon does increase but generally reaches a plateau, after not a long time.
There are also questions of excessive costs for attaining the increases. Powlson says their study indicates that “if you make really pretty drastic changes in land management then you could in fact get more than the four per mil rate.” But the measures were quite extreme for the real world, such as adding huge amounts of manure every year or going from a continuous arable cropping to a rotation with very long fallow periods or taking the land out of agriculture and letting it revert to forests or prairie. “In a world where we have to grow quite a bit of food, taking much land out of agriculture doesn’t seem like a feasible thing to do – perhaps on a small scale where you have erosion problems but not over huge areas of land.”
Increasing the manure distribution on land is obviously challenging (e.g. storing and transporting large amounts) but it can also bring about nitrate leaching and phosphorus pollution. The release of the potent nitrous oxide ghg also comes with manure deposition. Most fundamentally, transferring carbon from manure to soils does raise soil carbon content and brings about important benefits for agriculture, but it transfers existent carbon between stocks, so the mitigation benefits are questionable. However, letting crop residue reside in soil instead of burning it – one much highlighted soil carbon measure – is a clear mitigator on balance. Other measures such as no-till, are, on balance, true mitigators. Another recent study on tropical soils, “Soil carbon stock changes in tropical croplands are mainly driven by carbon inputs: A synthesis” in the March 2018 issue of Agriculture, Ecosystems and the Environment” was similar to Powlson’s European Rothamsted study in cautioning of overpromising on soil for carbon concentration abatement, but did mention significant soil carbon retention potential through enhanced crop rotation, with particularly strong carbon retention in the root zones of rotated crops systems.
Fundamentally, Powlson hopes that increasing soil carbon could be appreciated as a Sustainable Development Goal (SDG), pointing to understandings articulated by Canadian soil biochemist Henry Janzen, that it is the unique relationship of soil carbon and microorganisms who break down carbon in soil that gives soil good and porous structure, all the while transferring the suns energy captured via photosynthesis into the below ground earth, all plusses for agronomy.
Janzen has written that “soil organic matter is far more than a potential tank for impounding excess CO2: it is a relentless follow of C atoms, though myriad streams – some fast, some slow, wending their way through the ecosystem, driving biotic processes along the way”
A return to mixed landscapes where animal husbandry and plant agronomy occur near each other is one way to increase soil carbon that Powlson hopes will be promoted. “But if we are claiming,” says Powlson, “that we are actually going to cancel out CO2 from burning fossil fuels, actually we can’t do that.”
Colorado State University soil ecologist Keith Paustian, who specializes on soil carbon and also soil carbon monitoring, agrees with Powlson that increased sequestering carbon in soils can never be the central mitigation program and cannot offset fossil fuel emissions. However, Paustian remains bullish on soil carbon and feels it is a very promising component in an abatement portfolio for the future that would combine reducing emissions with measures to draw down atmospheric carbon . “There is a lot of land area where you could practice better land management practices and get benefits,” says Paustian, adding that existing conservation practices, such as cover crops and crop rotations, are effective. He adds that there are not technological barriers to increasing soil carbon.
Like Powlson, Paustian emphasizes effective soil carbon measures depend on the setting, but he believes soils carbon abatement might very well be economically promising in the long run. “There is no cheapy easy solution,” he says. “If we do direct air capture and maybe it costs 200 dollars a ton for CO2, how much can we change our land management systems if the value of storing additional carbon was $200 per ton of CO2?” Paustian reflects, “I think we can actually do a lot. I think potentially one can imagine a very different managed landscape.”
This future landscape would include breeding crops for deeper, more efficient carbon storage to supplement the conventional and well-supported breeding that focuses on yield increases and pest resistance. “In order to do things differently…that requires additional investment, but I think probably the breeders could do a lot on something they have not been asked to do,” says Paustian.
Inevitably, farmers will be asked to change practices, adding expenses to their already stretched account balances. It won’t be easy, but it is possible. “Farmers for many of these practices are going to need incentives at least to get the ball rolling. It is not going to happen by itself ; it will have to be incentivized,” Paustian adds.
Natural Resource Economics: A Starting Point For Soils
As an economist, Moran, too, is quite attentive to what farmer will do for soils health. He agrees with Paustian that policy incentives will be needed. There will also be behavioral challenges that industry psychologists can help with.
Moran outlines four steps for how to approach the economics of soil carbon for mitigation and sequestration. First, Moran says the beginning question to be addressed is what’s the technical potential. How much soil carbon can be sequestered in an unconstrained world. Secondly, how much of this technical potential is cost effective, that is it passes an economic potential test. Within this second inquiry are considerations of labor cost-effectiveness, opportunity costs (where other land uses are cheaper or more expensive). The third consideration is whether there is a behavioral barrier to realization of either of the first two considerations. Can you get farmers or herders to do it? The fourth step to consider that Moran offers for making soil carbon abatement viable on a large-scale is very key (and certainly lacking) and that is how much of what remains can be implemented or supported by a viable or sensible policy. “If farmers won’t see a benefit, they won’t do it,” Moran explains. “And even if that’s the case, generally farmers need a policy incentive, prod or nudge, so is there a policy incentive for helping them do it.”
“These are about four hurdles we probably have to step through to make sense of how much abatement we are actually going to get from soils,” Moran says.
Moran also adds three other major refinements are essential for soil carbon economics. First, property rights need to be tweaked or transformed to promote soil carbon. He explains: “Governments have been changing property rights in the U.K. and United States for last several decades, making farmers do more things which is subtly changing their property rights to their own land water pollution. We need that to pervade carbon emissions.” Moran adds that this raises questions of how fast can you change legal rights. But it can be done, with carrots and sticks, which resource economists and psychologists can help with.
Additionally, Moran says much more work needs to be done on monitoring carbon and soils and emissions from land, and this will be hard but necessary. It is a technical area that Paustian works on, which both Moran and Paustian feel is improving, but more research and development and more consistent monitoring, especially on farms, are essential. Currently, agroforestry is way ahead of soils in terms of MRV, monitoring, reporting verification.
Finally, Moran says “the other big glaring elephant in the room that would make this happen is global carbon pricing.” But in the meantime, there are other incentives for other public goods that could serve as models for moving the economic incentive for soil mitigation forward, like programs for wetlands mitigation and low grazing. Moran adds one idea is to reform agricultural subsidies to include carbon and another idea is to get more buy-in from the private sector on this would be a start.
Right now, Moran says, “we are in a space in which we are dislocated from the ultimate position.” And for the soil carbon future, natural resources economists have yet to weigh in mightily, and help nudge soil carbon mitigation and abatement to a viable future. But the day may come. “I think potentially there are ways that we can imagine a fundamentally different looking agricultural landscape in the future where healthy soils and carbon sequestration was a major goal that also drove investment…Those frontier technologies could be game changers,” Paustian says. “Looking a little bit longer term, if we reimagine our agricultural landscapes then the possibilities become much greater.”