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Can Compost Save the Climate?

A compost experiment that began seven years ago on a Marin County ranch has uncovered a disarmingly simple and benign way to remove carbon dioxide from the air, holding the potential to turn the vast rangeland of California and the world into a weapon against climate change.

Experiments on grazing lands in Marin County and the Sierra foothills of Yuba County by UC Berkeley bio-geochemist Whendee Silver showed that a one-time dusting of compost substantially boosted the soil’s carbon storage.

The research showed that if compost from green waste — everything from household food scraps to dairy manure — were applied over just 5 percent of the state’s grazing lands, the soil could capture a year’s worth of greenhouse gas emissions from California’s farm and forestry industries.

The effect is cumulative, meaning the soil keeps absorbing carbon dioxide even after just one application of compost, the researchers found. In theory, Silver calculates, if compost made from the state’s green waste were applied to a quarter of the state’s rangeland, the soil could absorb three-quarters of California’s total annual greenhouse gas emissions.

“For a lot of people, this sounds a little fantastic,” Silver said. “There’s nothing magic about it.”

Soil is a major source of carbon, “and we’ve been bleeding it into the atmosphere for many, many years through plowing, overgrazing and poor agricultural practices,” Silver said. “So anything we can do to get some of that carbon back into the soil is going to be beneficial.”

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