New Study Shows Organic Farming Traps Carbon in Soil to Combat Climate Change

Organic farms were found to have 26 percent more long-term carbon storage potential than conventional farms.


When it comes to mitigating the worst impacts of climate change, keeping excess carbon out of the atmosphere is the prime target for improving the health of our planet. One of the best ways to do that is thought to be locking more of that carbon into the soil that grows our food.

The scientific community has been actively debating whether organic farming methods can provide a promising solution. A 2010 paper published in the journal Ambio found that research about increased carbon sequestration due to organic farming methods was inconclusive, while a 2012 study in the Proceedings of the National Academy of Sciences (PNAS) found increased carbon sequestration in organic farm soils—though a 2013 letter in the PNAS disputed those findings, arguing that there were no carbon sequestration benefits related to organic farming.

A new study from Northeastern University and nonprofit research organization The Organic Center (TOC), though, has reached a different conclusion: Soils from organic farms had 26 percent more potential for long-term carbon storage than soils from conventional farms, along with 13 percent more soil organic matter (SOM).

For the study, which Civil Eats got early access to review, chemists Elham Ghabbour and Geoffrey Davies began by analyzing soil samples from over 700 conventional farms in 48 states. They made the alarming discovery that these samples contained little to no humic substances. Humic substances are one portion of soil organic matter, which is made up of decomposing plant and animal matter. Comprised of humin, humic acid, and fulvic acid, humic substances are a major component of healthy, fertile soil, giving it structure and water-holding ability, among other things. They’re built up slowly, over the course of many years, by living materials such as manure that are added to soil.

“They’re important because they’re one of the biggest places carbon can get stored,” said TOC’s Director of Science Programs, Jessica Shade, who is a co-author on the study. And storing carbon in soil provides what Shade calls a whole suite of benefits that are linked to soil health, including supporting beneficial organisms like worms; reducing erosion and compaction; and providing aeration, essential plant nutrients, and water retention.

After some consideration, Ghabbour and Davies hypothesized that the dearth of humic substances was due to the high-input practices inherent to conventional farming, such as tilling and the use of chemical fertilizers and pesticides. They worked with TOC to contact certified organic farmers and enlist them as “citizen scientists” in gathering soil samples from their own operations; in all, 659 organic soil samples were collected from 39 states.

“Because organic farms are regulated by the United States Department of Agriculture (USDA) and use certain practices” such as crop rotation, letting fields lie fallow, fertilizing with compost, and maintaining a buffer between organic and conventional crops, as well as adhering to a three-year waiting period before qualifying for certification, “this was a great control group for testing this hypothesis,” said Shade.

Ghabbour and Davies devised a method for testing not just the overall amount of carbon in the samples—other researchers have already done this, though on a much smaller scale than this nationwide effort—but of those humic substances specifically. Since these can remain in the soil for hundreds, if not thousands, of years, they provide highly stable pools of carbon to support living and growing organisms.

“Soil is the biggest sink of carbon, bigger than the atmosphere and the oceans,” said Davies. And yet so far, “there have been no soil labs in the U.S. doing the kind of testing we’ve done—it wasn’t easy to do it on a big scale. But if they really want to know what the quality of soil is, they’ll want to know how much carbon it’s able to hold.” He and Ghabbour hope their testing methods, along with the importance of the information they’ve yielded, “will transform the industry,” he says.

“We already know that [conventional practices] like using [synthetic] fertilizers contribute to climate change,” said Davies—they deplete soil of carbon, which is then released into the atmosphere. But he and his team at Northeastern hope their new study might actually provide a roadmap to mitigating it.

“No one has ever compared this many organic and conventional soil samples before, or looked at these subsets of total organic matter,” said Michel Cavigelli, a soil scientist at the USDA who was not involved with the study but did review an embargoed copy of the full findings. Though he thinks there may be some criticism of the researchers’ “less rigorous” sampling methods, he said the large geographic coverage of samples makes up for that. Overall, he said, the study was a positive “first step that shows us [where] we need to look in more detail in more controlled studies, and this gives us the impetus to do that.”

As for how long it might take to see results on farms that undergo a transition to organic practices, Shade offered a reserved response. “To build up humic substances that will impact climate change is going to take decades,” she said. “But the side benefit is that as people start using the [organic] techniques that will sequester carbon, they’ll also be building healthier soil. And those benefits are exciting and tangible.”

Ghabbour and Davies’ full study will be published next month in the journal Advances in Agronomy; meanwhile, the Northeastern researchers are contemplating the next leg of their soil research journey.

“What I’d like to do next is to see if the humic substances in organic soils are the same as in conventional soils,” said Davies. If they differ, he says, that will be another indication that with conventional farming practices such as fertilizer use, “we’re going against nature.”

[Editor’s note: This post has been updated to clarify the scientific findings about farm-soil carbon sequestration.]

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  1. Monday, September 11th, 2017
    Thanks for the good article. You have made an effort to be balanced, but the arguments you cite in favor of chemical farming do not stand up to long-term or global scrutiny. Likewise, organic farming is a step in the right direction, but it alone is not sufficient to address our carbon, soil, food, energy and water problems. The correct solution is access to land, in order to develop perennial mixed gardens which include forest, trees, vegetables, berries, fruit, nuts, seeds, flowers, bees, etc. Not everybody wants to be a gardener, but those who do must be allowed to do it, because it results in a more productive and efficient use of our limited land and resources.

    Here's why the PNAS letter is wrong. It says that organic soil has more C because it applies more manure, and therefore is not an equal measure with chemical farming which does not apply manure. But applying organic compost which returns C to the soil is exactly the point. Chemical farms are not doing that. Therefore the study stands on its original assertion—organic practice increases C in soil. Secondly, its assertion that organic farming produces less than chemical farming is only correct if you ignore the external energy and land costs of producing agricultural chemicals, and also ignore the resulting pollution and emissions which will lower future yields and damage human health.

    They are wrong on another point here, because chemical farming produces less nutrition. There are studies on this but I do not have time to cite them all here now. The result is high levels of micronutrient deficiency including well documented iron-deficiency in India. Whereas traditional farming produced a large mixture of leafy greens, pulses and nuts, industrial monocrops do not provide the correct nutrient mixture for human health.

    I don't think the authors are chemical PR folk, but they are limited in their view. They are anxious to feed people, and think that chemical farming is the best way to do it because it produces more tons of food commodity which can be measured and controlled from their academic ivory tower in the West. It is great to want to feed everyone, but this should be done in a way that 1) provides adequate nutrition and 2) protects future generations. Chemical farming on both points has been decisively and conclusively proven wrong.

    To summarize the literature, studies favoring chemical farming typically ignore the future cost and the external cost of chemical industrial methods. They may be motivated by good intentions, but they are scientifically incorrect.

    Also, the comparison between chemical farming (a.k.a "conventional farming") and organic farming is a straw man. Organic farming is a move in the right direction, but it cannot account for the full needs of a prosperous, sustainable people much more than chemical farming can. To shift into sustainable food production, many more people will have to be involved in growing their own food. Our focus here should be:

    ACCESS TO LAND.

    The equitable distribution of land for the purposes of small, garden-scale agriculture is the only way to feed the global population. Technocratic studies about yields are not necessary to prove the point. Anyone who has seen a productive garden knows that it produces 1000 times more than an equivalent area of cattle pasture or wheat field, and with the correct combination of nutrients. A single mature fruit tree can produce 200kg a year. Even a diet of only fruit provides more nutrition than a diet of only rice. But studies will also validate my assertions, if you care to search for them.

    We must think ahead now. Fruit and nut trees take time to mature, and require constant stewardship by people. People need equitable, secure access to land, in order to cultivate perennial gardens which can supply our needs.

    Discussing organic practice is fine, but it alone will not supply our population with enough food, nor address the broader range of inequity, pollution and emissions which results from logistical costs and mechanized production. Equitable distribution of land, so that each person can establish their own garden, is both possible and necessary. To begin, we should look to underpopulated countries like Australia, Kazakhstan, Canada, Argentina and Russia. Further, we should look to revegetate non-arable areas in order to provide human habitat.

    We enough ingenuity and resources to pursue these possibilities. But it requires a shift of focus from technological, high-density, centralized ideas, towards natural, spread out, decentralized settlement patterns. Technology can help us communicate with one another as we spread, provide water access and energy in difficult regions, but we should ultimately plan to phase out manufactured technological devices, because of the costs involved in their production and disposal.

    In conclusion, your article is good and well-balanced. But the arguments for chemical farming to not stand up to long-term or global scrutiny. Likewise, organic farming in itself is not sufficient to account for all the challenges we face. Access to land to encourage natural mixed gardens is both more productive (output/input) and more efficient (yield/ha). On every development measure (resource use, economy, nutrition, health, sustainability, ecological stewardship, etc.), low-input mixed gardening is a positive program. Not everybody wants to grow their own abundance right now, but the people who do should be given the land and opportunity to do so.
  2. Tuesday, September 12th, 2017
    I am currently living in France where the topics of soil health and the conflict between conventional and organic farming are ubiquitous. I hope to see and hear more talk about the connection between soil health and carbon sequestration.

    Thanks for the good read.

    Elise Rothman d'Hauthuille
  3. Virginia Pact Richter
    Tuesday, September 12th, 2017
    Organic does not mean regenerative. The three core principles of which are: armour on the soil (soil always covered), no-till (don't disturb the soil food web) and biodiversity with living roots in the soil as much of the year as possible.
    Too many organic farms have bare soil and some tilling. Often there is not enough biodiversity to protect the plants from pests and organic pesticides are used.
    Regenerative or Restorative Agriculture has the potential to store much more carbon in a shorter period of time with less labor and higher profit. I call it organic plus!
  4. Stanlee Cox
    Tuesday, September 12th, 2017
    HOW TH HELL DID FACTORY CHEMICAL FARMING BECOME KNOWN AS CONVENTIONAL?????? That is such a farce. It is like calling our Corporate Pharmacology, Traditional Medicine!

    News flash: Organic farming was always the way of farming until less than 50 years ago!! THAT IS CONVENTION. THAT IS TRADITION. Call the farming practices that are ruining our health and our planet what they are! SOULLESS CORPORATE GREED FACTORY FARMS.
  5. Iean Russell
    Tuesday, September 12th, 2017
    Very interesting study. The results need full exposure to scientific debate and complementary work to extend and test the findings. This is an area with huge significance for the future. No need to dispute whether reforestation or soil amelioration through changed farming practices yields the biggest returns. Farmers might change their ways, but they won't be changing wholesale to forest production. We need investments in mitigation for all kinds of land use
  6. Wednesday, September 13th, 2017
    Its difficult to believe that after learning the importance of Carbon for infiltration and storage, that science has dragged its feet on this for so long. Someone has to ask, " was it a deliberate strategy at some point, to sell more inputs" . If it was, it has run the planet dangerously close to ruining a huge amount of prime soils, the really rich ones holding up longer, poorer, already in trouble.
  7. Richard L Scharf
    Friday, September 15th, 2017
    I never had any doubt that soils on organic farms contain higher amounts of organic matter than on conventional farms. My question is, what inputs are required for this? Full carbon accounting is necessary.

    How much in the way of organic matter additions are required? What is the availability of suitable organic matter, and does it limit the potential for the adoption of organic farming methods? What would the fate of those organic amendments be if they weren't used in organic farming? How much in the way of fossil fuels to spread and incorporate it? How do fossil fuel inputs compare to those on conventional farms?

    This ground-breaking study is no surprise. If what has been reported here sums up the study, a lot is missing before anyone should view organic farming as an important way to sequester atmospheric carbon.
  8. Tuesday, September 19th, 2017
    This research did not control for different soil textures nor differences in manure use between conventional and organic farms. Also, conventional farm soils represented 456 more counties than the organic soils meaning the organic soils were relatively concentrated geographically compared to the conventional soils. The conclusions are not justified.