2017-09-12 |

Organic farms store more carbon in the soil and for longer, study finds

Soil Organic soils have higher levels of soil organic matter and humic substances (Photo: CC0)

Soils on organic farms sequester more carbon and for longer periods of time than soil from conventional farms, new research suggests. A large-scale field study conducted in the United States shows that organic soils have significantly higher levels of humic substances, which are very effective in locking away carbon in long-term reserves. The study, directed by The National Soil Project at Northeastern University in collaboration with The Organic Center, found that soils from organic farms had 26% more long-term carbon storage potential than soils from conventional farms. The results will be published on October 1 in the peer-reviewed journal Advances in Agronomy. According to the authors, this is the first time scientific research has given an accurate picture of the long-term soil carbon storage on organic versus conventional farms throughout the U.S., since most studies focus only on individual farms or total soil organic carbon.

The researchers at Northeastern University compared over 1000 soil samples from organic and conventional farms across the US, taking into consideration different farming methods, crops and soil types. They used data from the National Soil Project, which has been measuring the organic soil content of primarily conventional soils since 2008, as well as soil samples of organic farmers who acted as so-called “citizen scientists”. In 2015 and 2016, those farmers collected 659 organic soil samples from 39 states. Similar to previous studies, the result was that soils from organic farms have 13% more soil organic matter. But the research team also measured humic substances, in particular their main components fulvic and humic acid. “We don’t just look at total soil organic carbon, but also the components of soil that have stable pools of carbon – humic substances, which gives us a much more accurate and precise view of the stable, long-term storage of carbon in the soils,” said Dr. Jessica Shade, Director of Science Programs for The Organic Center. The study showed that fulvic acid and humic acid were consistently higher in organic than in conventional soils. On average, organic farms had 44% higher levels of humic acid, the component of soil that sequesters carbon over the long term, and 150% more fulvic acid than soils not managed organically.

The authors highlight that organic agriculture can make a real difference in climate change mitigation due to the higher levels of humic substances. These substances resist degradation and can remain in the soil for hundreds and sometimes thousands of years. The more humic substances in a soil, the longer that healthy soil is trapping and keeping carbon out of the atmosphere. “These results highlight the potential of organic agriculture to increase the amount of carbon sequestration in the soil, and by doing so help decrease a major cause of climate change,” said Dr. Shade. According to Dr. Tracy Misiewicz from The Organic Center, practices commonly used in organic farming such as the use of manure and legume cover crops, extended crop rotations, fallowing and rotational grazing, are likely involved in increasing humic substances in soil. Dr. Geoffrey Davies, leader of the National Soil Projects, told Civil Eats: “What I’d like to do next is to see if the humic substances in organic soils are the same as in conventional soils. If they differ, he said, that will be another indication that with conventional farming practices such as fertilizer use, “we’re going against nature.” (ab)


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