A new study shows organic farms store more carbon in the soil and keep it out of the atmosphere longer than conventional farms.
The findings of the study by Northeastern University’s National Soil Project and The Organic Center suggest organic farming could help reduce one of the causes of climate change.
Eighty percent of the Earth’s terrestrial carbon is stored in soils, and human management practices can deplete the soil’s carbon stores by releasing it into the atmosphere. Agriculture in particular has been linked to large losses of soil carbon worldwide, the researchers said.
While other studies have found that soils from organic farms have more soil organic carbon, very little research has been done on the amount of total soil organic carbon found in the form of stable humic substances, the researchers said.
“This study is truly groundbreaking,” said Jessica Shade, director of science programs at The Organic Center.
“We don’t just look at total soil carbon but also 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 soil,” she said.
Total soil organic matter is not necessarily an accurate proxy for understanding long-term, carbon-storage ability in the soil. The study is important because it quantifies the molecules important for long-term carbon storage in soils, the researchers said.
The soil’s total organic carbon is made of two distinct pools — the labile carbon pool and the humic substances pool. The labile carbon pool is short-lived and constantly cycling in and out of plants and entering the atmosphere as carbon dioxide.
The other pool is humic substances, formed when organic matter biodegrades. The carbon molecules from humic substances are not cycled into the atmosphere rapidly and instead are stored in the soil for longer periods and represent a more stable pool of soil carbon.
Humic substances, made up of carbon and other elements, resist degradation and can remain in the soil for hundreds and sometimes thousands of years. The more humic substances, the longer that healthy soil is trapping and keeping carbon out of the atmosphere, the researchers said.
The study measured 659 organic soil samples from 39 states and 728 conventional soil samples from the 48 contiguous states. Researchers measured total soil organic matter and humification — the process by which organic matter is transformed into more stable humic substances.
They found organic soils had higher levels of all soil organic matter and humic substances. The humic substances included in the study were humic acid and fulvic acid.
Humic acid is more stable than fulvic acid and is one of the best measures of the long-term storage of carbon in the soil, they said.
The study found on average soils from organic farms had 13 percent more soil organic matter; 150 percent more fulvic acid; 44 percent more humic acid; and 26 percent greater potential for long-term carbon storage.
“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,” Shade said.