THE "DIRT" ON GLOBAL WARMING.

• Author: Mcneil, Maggie
• Position: Carbon sequestration by organic soil

Organic soil cuts agriculture's contribution to climate change.

Soils on organic farms store away appreciably larger amounts of carbons--and for longer periods--than typical agricultural soils, according to a study directed by Northeastern University in collaboration with The Organic Center, which provides a significant proof point that organic agricultural practices build healthy soils and can be part of the solution in the fight on global warming. The data was published in Advances in Agronomy.

One of the largest field studies of its kind, the study pulls together more than 1,000 soil samples from across the nation. One of its most-compelling findings is that, on average, organic farms have 44% higher levels of humic acid--the component of soil that sequesters carbon over the long term--than soils not managed organically.

Agriculture is one of the main causes of the depletion of carbon in the soil and the increased presence of carbon in our atmosphere. Organic farming can play a key role in restoring soil carbon and in reducing the causes of climate change.

Working with Elham Ghabbour and Geoffrey Davies, leaders of the National Soil Project at Northeastern University, The Organic Center contacted organic farmers who acted as "citizen scientists" to collect organic soil samples from throughout the country to compare with the conventional soil samples already in the National Soil Project's data set. Altogether, the study measured 659 organic soil samples from 39 states and 728 conventional soil samples from all 48 contiguous states. It found that all components of humic substances were higher in organic than in conventional soils.

'This study is truly groundbreaking," says Jessica Shade, director of Science Programs for The Organic Center. "We don't just look at total soil organic carbon, but 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.

'To our knowledge, this research is also the first to take a broad view of organic and conventional systems, taking into account variation within management styles, across crops, and throughout the U.S. It gives a large-scale view of the impact of organic as a whole, throughout the nation."

Adds Davies: 'We were focused on developing and adopting reliable methods of soil analyses for this national project. It was a huge, cooperative effort involving hundreds of sample...