Biochar aids soil fertility, keeps carbon in earth Charcoal holds promise as a way to keep soil rich and carbon out of the atmosphere

Biochar Illustration Biochar Illustration Photo: Harley Soltes Photo: Harley Soltes Image 1 of / 5 Caption Close Biochar aids soil fertility, keeps carbon in earth 1 / 5 Back to Gallery

After many afternoons digging in The Chronicle's garden, I've grown accustomed to the strong winds that blow through the intersection of Fifth and Mission. Yet I couldn't help but notice the dusty, depleted soil that barely clumped in my palm. With 6-year-old dirt harboring very little organic matter, our planters were looking more like dust bowls.

Like many container gardeners, we've struggled to maintain soil fertility on our San Francisco rooftop. Typical potting soil contains a mixture of sand, compost and perlite. After just a few years, nutrients leach out with water and what's left is spent compost and soil looking as if it belongs in a sandbox. Some may say, "Bring out the Miracle-Gro," but if the soil can't retain the nutrients, it's only a temporary pick-me-up.

I sought guidance from our mentor, S.F. master gardener Fred Bové, who was already two steps ahead when he arrived. He plopped down two hefty bags of biochar, pulled out a handful of dark dirt speckled with fragments of charcoal, and introduced me to an organic alternative for gardeners looking to enhance fertility.

"Think of it as a savings account for your soil," he said.

The benefits don't stop there. This high-quality charcoal is also being hailed as a tool to fight climate change and produce renewable energy. It's the subject of the U.S. Biochar Conference, which brings scientists, policymakers, farmers and entrepreneurs to Sonoma State University in July.

To me and perhaps much of the local population, the word "biochar" is just as foreign as the Brazilian turf from which it originates. Near the end of the 19th century, researchers found highly fertile sites in the Amazon that contained astounding levels of carbon compared with surrounding soils.

Beneficial microbes

According to studies compiled by Cornell University, pre-Columbian Indians created the rich dark earth revered as terra preta de indio. The Indians smoldered crop waste and leftover food in pits where there was little oxygen. Rather than burn it to ash, the low temperatures converted the waste into carbon-rich charcoal whose porous structure provides a haven for beneficial microbes and stores nutrients.

Today the process is simulated by pyrolizing organic material - heating it at relatively low temperatures in a closed container. As the waste heats up, it gives off gas that can be captured and used as clean energy. The charcoal left behind, biochar, is gaining attention for its ability to hold carbon back from the atmosphere by storing it in the soil.

When plant waste decomposes, the carbon dioxide retained during photosynthesis is normally released back into the atmosphere.

Trapping carbon

"Biochar production interrupts the natural carbon cycle by taking the plant material with its embodied carbon and processing it into a form that is very stable and will not decay anywhere near the natural rate," said Ray Gallian, director of the Sonoma Biochar Initiative, a nonprofit promoting biochar use in Sonoma County and host of the upcoming U.S. conference.

Biochar's porous nature also helps soil retain water, thereby reducing fertilizer runoff.

"Fertilizer regularly washes away with the rain. However, if the soil has high carbon content from compost or char, the fertility is bound in the soil and available to plants for a longer time. The carbon works like a buffer, allowing your fertilizer to stretch over longer periods of time," said Trip Allen, president of Energy Anew, a San Rafael company that manufactures Biocharm and, along with Sonoma Compost Co. in Petaluma, sells it to home gardeners.

Gallian and Allen are just two of many local advocates for biochar. Having previously used Biocharm, the Regenerative Design Institute of Bolinas, a pioneer in sustainable agriculture, now uses homemade biochar to revive vegetable beds.

"We grind the biochar up and put it in worm castings. We also make biochar balls to put around the plant's roots," said Penny Livingston-Stark, the institute's co-founder. "In general, it perks up the plant. Edibles that were once not doing so well went from dull to vibrant."

Still in its experimental phase, biochar is not widely available. However, its potential as a source of renewable energy and soil rehabilitation has caught the attention of entrepreneurs and venture capitalists as well as organizations looking to aid farmers in developing countries and discourage deforestation.

Not a cure-all

Amid all this enthusiasm, some environmental experts, including Albert Bates, author of "The Biochar Solution" (New Society Publishers, 2010), warn that biochar production should not be viewed as a cure-all and does not come without risks. If transported long distances or produced in a large kiln, the process could generate more CO2 than the biochar sequesters. The closer you can get it to the farm the better, says Bates.

He also warns that without standardized criteria, companies can use inorganic, potentially toxic feedstock or genetically modified tree plantations during production.

"USDA and other authorities have left a large void unfilled, and businesses will fit it the cheapest way they can," says Bates. However, in May the International Biochar Initiative drafted protocol and material requirements that would dictate what deems a substance biochar.

Vandana Shiva, an environmental activist, physicist and founder of Navdanya International, a network of seed keepers and organic producers, cautions that industrial biochar production shouldn't be proposed as a magical solution to climate change. She advises proponents to avoid a reductionist carbon mentality and keep in mind that plants, like humans, need all the essential micronutrients and trace elements.

"We need to remember that calcium, magnesium and copper, the mycorrhizae and the earthworm are also part of the soil's life, not just carbon," Shiva said.

Will Bakx, soil scientist and co-owner of Sonoma Compost Co., also stresses that biochar alone will not guarantee healthy soil.

"Biochar works as a hotel for microorganisms. If there are no guests, the hotel will be empty," he said. "A good supply of compost will provide the guests."

Keeping these facts in mind, we've prepared a future fava bean plot with a compost-biochar blend, while testing remedies such as adding Epsom salt to our magnesium-starved lemon trees and worm castings to our grape vines.

There is no one way to revive the soil. By combining the advice of these experts, we hope to keep The Chronicle's garden thriving for years to come.

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