Organic Farming Stores Carbon Better Than Trees

The Rodale Institute’s 23-year comparison of organic and conven­tional cropping systems confirms that organic methods are far more effec­tive at trapping and holding carbon dioxide, a greenhouse gas, in the soil as beneficial organic matter.

Launched in 1981, the Farming Systems Trial (FST) is a 12-acre, side-by-side experiment, comparing three agricultural management sys­tems: one conventional, one legume-based organic, and one manure-based organic. In 23 years of continuous recordkeeping, both organic systems have shown an increase in soil car­bon of between 15-28%, while the conventional system has shown no statistically significant increase. For the organic systems, that translates into more than 1000 lbs of captured carbon or about 3670 lbs of CO2 per acre-foot per year, not even count­ing the reductions in CO2 emissions represented by the organic systems’ lower energy requirements.

An analysis of FST energy inputs, conducted by Dr. David Pi­mentel of Cornell University, found that organic farming systems use only two-thirds of the energy required by conventional farming systems, largely because of the massive amounts of en­ergy required to synthesize nitrogen fertilizer.

In the FST, soil carbon levels increased more in the manure-based organic system than in the legume-based organic system, presumably because of the incorporation of ma­nures. The study also showed that soil carbon depends on more than just total carbon additions to the system — cropping system diversity or the carbon-to-nitrogen ratio of inputs and their decay rates may have an effect.

The work of another Rodale re­search collaborator, Dr. David Douds of the Agricultural Research Service, suggests that healthy mycorrhizal fungi populations in the organic sys­tems also slow down the decomposi­tion of organic matter, thus retaining carbon.

The carbon cycle

Scientists are developing an increasingly sophisticated picture of the global carbon cycle. Total carbon storage provided by different parts of the global system — terrestrial veg­etation, the surface ocean, the deep ocean — have been quantified, as have the annual fluxes of carbon among them. CO2 emissions from hu­man and animal activities now stand at about 8.9 billion US tons per year, while net atmospheric CO2 accumula­tion is 3.5 billion US tons. In other words, 40% of annual human-induced carbon emissions contribute to build-up, while the remaining 60% are ab­sorbed by the oceans and plants.

Farmlands beat forests as a carbon “sink”

Proposals to expand natural carbon sinks as a partial remedy for global warming initially focused on reforestation. Changes in land use, including the loss of forests to till- age and grazing, were known to be a major contributor to the greenhouse effect. As recently as the 1970s, total accumulated carbon emissions from changes in land use exceeded total emissions from the burning of fossil fuels. Politicians hoped that escalat- ing fossil fuel consumption could be balanced by vast forests breathing in all that CO2. Data like those emerging from the Farming Systems Trial, however, are revising that idea. The soil itself may make more of a difference than what’s growing in it. On a global scale, soils hold more than twice as much carbon (an estimated 1.74 trillion US tons) than does terrestrial vegetation (672 billion US tons). Practices like re- duced tillage, the use of cover crops, and incorporation of crop residues can further dramatically alter the carbon storage of arable lands.

From a net loss of soil carbon to a net gain in one easy step

Dr. David Pimentel calculates that US agriculture currently emits about 925 billion pounds of carbon dioxide each year from crop and livestock production. So, what would happen if all those US acres converted to organic production? The British Royal Society has estimated potential carbon dioxide (CO2) sequestration on the world’s 2.5 billion acres of agricultural soils at 6.1 to 10.1 billion US tons per year for the next 50 years. Another estimate puts the total amount of CO2 that could be captured in developing countries at 1.7 billion US tons over the next dec- ade. In short, carbon sequestration via adoption of organic agriculture could have a substantial impact on global warming. Organic farming incidentally also reduces erosion, minimizes impact on native ecosystems, and improves farmer livelihoods. Compared to for- ests, moreover, agricultural soils may be a more secure sink for atmospheric carbon, since they are not vulnerable to logging and wildfi re.

Carbon credits for organic

The Rodale Institute and the Pennsylvania state departments of ag- riculture and environment have joined forces to explore mechanisms by which farmers and landowners could quantify the carbon sequestered on their properties and receive a payment from the state or federal government for “ecosystem services provided.” Farmers might even participate in emerging ‘carbon-trading’ markets around the world. Such markets are rapidly expanding in the European Union and elsewhere. (See, for exam- ple,, a greenhouse gas brokerage fi rm based in London.) However, the whole business of credit for carbon-sequestration activi- ties under the Kyoto accord is prob- lematic, because of the lack in 1997 of good carbon inventory data that could be factored into the nation-by-nation emissions-reduction targets. Unfortunately carbon sequestra- tion by organic farming, like carbon capture through reforestation, is a short-term or ‘bridge’ solution, a way of buying time for more fundamental changes. Ultimately, global climate change can only be fully addressed through rationalization of energy policies, reductions in fossil fuel con- sumption, and improvements in emis- sions-control technologies. Among the possible short to medium term solutions, however, organic farming has a lot going for it. Compared to expensive, ex- perimental, high-technology projects like underground injection, global transitioning to organic farming looks cheap and easy. It’s a step toward solving carbon build up and climate change that brings with it a wealth of other environmental benefi ts.

Fast Facts

n If only 10,000 medium sized farms converted to organic production, they would store so much carbon in the soil that it would be equivalent to taking 1,174,400 cars off the road.

n Converting the US’s 160 million corn and soybean acres to organic produc- tion would sequester enough carbon, 293 million tons of CO2, to satisfy 73 percent of the Kyoto targets for CO2 reduction in the US.

n American agriculture as currently practiced emits a total of 1.5 trillion pounds of CO2 annually into the atmosphere. Converting all US cropland to organic would give a net INCREASE in soil carbon of 734 billion pounds.

Adapted with permission from the original article, available in full at All material ©2003, The Rodale Institute

[From WS March/April 2004]

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