The Sequestration Solution

Guido Frosini reaches down and wraps his fingers around a clump of orchard grass. He tugs at the foot-tall stalks, snapping them a few inches from the surface and leaving a tidy clump of green stubble. He’s not trying to kill the plant. Rather, Frosini is demonstrating how his cows—currently dining elsewhere—benefit the pasture by grazing it under careful management.

Though not technically a native variety, perennial orchard grass is a welcome sight on this hundred-acre patch of rural West Marin known as True Grass Farms. Cows love the nutritious plant but, more important, it’s also a clear sign that Frosini’s soil is getting healthier. For that, he owes a small debt of gratitude to Whendee Silver.

Since 2018, Frosini, whose family’s ties to the land date to 1867, has overseen the application of thin layers of compost on 12 of his acres. He hopes this will reverse soil compaction, improve water retention, increase grass and tree productivity, and draw atmospheric carbon into the soil.

Though Frosini has never met Silver—a professor in the Rausser College of Natural Resources’ Department of Environmental Science, Policy, and Management (ESPM)—her research has not only informed his soil treatment but also, more indirectly, helped to fund it. By establishing through rigorous science that applying compost to actively grazed rangelands helps sequester atmospheric carbon in the soil, Silver has provided a foundation for programs across the country that pay people like Frosini to spread compost.

“When you add compost to soils, it increases plant growth, helps maintain water-holding capacity and nutrient supply, and reduces erosion,” Silver explains. “You end up with more organically rich soil and more nutrients, so the plants grow better, and those plants are pulling carbon dioxide out of the atmosphere and helping to slow climate change.”

True Grass Farms, which, among other products, sells “grassland-fed and -finished” beef, proves Silver’s point. Frosini received a grant in 2018 from California’s Healthy Soils Program, a four-year-old initiative directly informed by Silver’s work, that helped cover the cost of buying two years’ worth of compost for his first five acres.

“It’s such a long process to build soil, and it takes so little to take it away,” Frosini says. “The function of the carbon farm plan allows us as ranchers to take on certain tasks that may not seem profitable but are necessary if we’re going to sustain food production in a more holistic, continuous way, and not just on a generation-to-generation basis.”

Frosini is already seeing a return on the compost applications—even beyond the arrival of scattered perennial grasses. “From a producer’s standpoint, you can see the direct benefits,” he says, noting that where compost has been spread, he’s seen more-uniform cattle grazing and a general increase in plant productivity and crop production.

Below the surface, there are even more benefits. Petaluma-based nonprofit Point Blue, which is helping to monitor some less-obvious changes resulting from compost applications through the Healthy Soils Program, has already reported less soil compaction compared with untreated plots. It is also measuring increases in carbon levels in Frosini’s soil, but as of press time results were not yet available. Frosini says he plans to continue spreading compost—now produced on-site—across his entire ranch, a quarter inch deep and five acres at a time.

According to a 2018 study in the journal Science Advances by Silver and her colleagues at UC Berkeley and the Lawrence Berkeley National Laboratory, carbon sequestration on agricultural lands through organic soil amendments and other practices—for example, reduced tillage and use of cover crops—could have an appreciable impact on global surface temperatures.

Silver’s team used a combination of climate and ecosystem modeling to determine that, by helping to store new carbon, such agricultural practices could reduce global temperatures by up to a quarter of a degree Celsius by 2100. The greatest cooling effect was achieved when enhanced soil carbon storage was combined with greenhouse gas emissions reductions in other sectors.

A previous study of Silver’s in 2013 found that adding compost to just 5 percent of California’s rangelands could sequester the equivalent of 28 million tons of carbon dioxide over a three-year period, offsetting nearly one year of emissions from the state’s agriculture and forestry sectors.

In recent years, Silver’s work has earned her the attention of such media outlets as the New York Times, Slate, and NOVA. Most articles on her research and the broader practice of “carbon farming,” a concept she has helped to popularize, reference these impressive figures. And inevitably, as in a New York Times headline, the question is raised: Can compost save our planet?

Tempting as it may be to sell it as the solution to what remains humanity’s greatest challenge, Silver herself is more circumspect. “Combined with emissions reduction, it’s part of a portfolio to help slow climate change,” she says. “We need to come up with multiple ways in which we can do that, and this is just one. But it’s one that makes really good sense and has a lot of benefits.”

Coincidentally, the research behind the policies that helped fund the compost applications that are now sequestering atmospheric carbon at True Grass Farms and elsewhere all began about 20 miles from Frosini’s ranch. In 2007, a landowner named John Wick and a rangeland ecologist named Jeff Creque—whom Wick had hired to help him rehabilitate his ranch at the southern end of Marin’s Nicasio Reservoir—reached out to Silver. At the time, she was already established as an expert in soil biogeochemistry: the study of physical, chemical, and biological processes in the soils of different landforms and ecosystems.

Wick wanted to know if Silver could determine whether the carefully managed cattle-grazing program he’d recently implemented on his 540-acre ranch, which appeared to be improving productivity and biodiversity, was also putting carbon in the ground—and if so, how much? Silver agreed to investigate, and the rest is history.

Preliminary research throughout Marin and Sonoma Counties indicated that ranches using organic soil amendments (primarily manure but also compost) had higher levels of carbon in their soil. Spreading manure isn’t attractive as a sequestration tool because it releases lots of nitrous oxide as it decomposes. But compost doesn’t pose that problem.

In 2008, Wick, Creque, and Silver formed the Marin Carbon Project to further study soil carbon and its sequestration through compost applications, with Silver serving as lead scientist. The first applications began that year on two grassland study sites: one on Wick’s coastal ranch and another in the Sierra foothills.

Five years later, early data indicated that it had worked, paving the way for new incentives for composting and carbon farming through both California’s Healthy Soils Program and the federal Environmental Quality Incentives Program.

Subsequent research led by Silver through the Marin Carbon Project has also proved influential. It has informed policies that will help California develop adequate supplies of compost. It convinced the state to include rangeland soil carbon sequestration in its climate change mitigation activities for the first time, implementing concrete targets for emissions reductions from natural and working lands. And it has supported initiatives similar to the Healthy Soils Program in other states.

“Whendee’s research opened the window on an understanding that there was real potential to sequester significant quantities of carbon on working landscapes through management,” Creque says. “While the original research focused on compost, once we saw the potential, we realized there are many, many ways to increase carbon capture on working landscapes.”

While completing her PhD, Rebecca Ryals, PhD ’12 ESPM, worked closely with Silver on field experiments, reviews of existing scientific literature, and five published articles. This early work laid a foundation for ongoing research in Silver’s lab as well as Ryals’s early career as a faculty member at UC Merced. She now teaches agroecology and continues to study innovative ways of mitigating climate change through soil and nutrient management. “When we first started [working together], we got a lot of skepticism about the use of soil carbon as a climate strategy,” Ryals says. “Now that project has shown that it’s possible.”

More recently, she says, it’s been gratifying to see so many people (and media outlets) talking about compost application and climate change—an evolution that has given her hope for other unconventional ideas that may also play a role. “I’ve been trying to use that model to understand other untapped, unstudied solutions,” she says—for instance, using biochar or sanitized human waste to improve soil health and reduce atmospheric carbon, or applying compost on steep slopes and in Central Valley orchards.

In 2015, Silver began collaborating with graduate student and lab member Allegra Mayer, now in the final year of her PhD. Mayer served as lead author of the 2018 Science Advances paper modeling global temperature decreases and is currently working on a follow-up project with a focus on California.

She is also collaborating with Silver and researchers at the Lawrence Livermore National Laboratory on a study that will use carbon isotopes and a process called accelerator mass spectrometry to gain insight into a central question about which little is known: “Once you sequester carbon in soil, how long will it stay there, assuming that you’re not specifically disturbing it?” Mayer says.

Finally, results from Silver’s 10-year resurvey of the original study plots on Wick’s ranch and in the Sierra foothills are also pending. Originally set to be submitted for publication earlier this year, the paper has been delayed by lab closures associated with COVID-19. Preliminary results, however, are promising. Silver says she can’t discuss the findings publicly until they are released.

In the meantime, she has plenty to keep herself and her lab of 18 members occupied. For one, Silver also serves as co–principal investigator of the UC Working Lands Innovation Center, a multicampus program established in late 2018 with a three-year, $4.7 million grant from the state of California. Its charge is to research and deliver scalable, “shovel ready” methods of using soil amendments—including compost, ground rock, and biochar—on agricultural lands to capture carbon in soil and reduce emissions of carbon dioxide and other greenhouse gases. This in turn supports the state’s official goal of bringing net carbon emissions to zero by 2045.

Along with her high-profile work on soil carbon sequestration, Silver has long led research into many other areas of biogeochemistry and ecology, in both the U.S. and tropical regions.

Over the past three decades, she has written or coauthored more than 170 papers. The complex interactions between soil and ecosystem dynamics, greenhouse gas emissions, land-management decisions, weather events like hurricanes and droughts, and climate change have long been on Silver’s mind. But about 15 years ago, she says, she came to the sudden realization that simply studying and measuring climate change wasn’t enough.

“I looked up and said, ‘You know, we need to do something about this. We need to dedicate some of our research to figuring out ways in which we can slow climate change,’ ” says Silver. “So we added that into our research program, to begin looking at what lowers greenhouse gas emissions in natural and managed ecosystems. Can we understand that thoroughly enough to have it become standard management practice?”

In this sense, it’s not compost or even soil that motivates Silver. What drives her is something bigger, something she mentions again and again: solving the climate crisis. Her urgent yet holistic perspective is reflected in her teaching at Berkeley, particularly a class called Bending the Curve. Offered at several UC campuses, this completely online course about climate change solutions may eventually be brought to Rausser College as a regular offering. For her work in both the field and the classroom, Silver was recognized as UC Berkeley’s first Faculty Climate Action Champion in 2015.

“We have to realize that emissions reduction alone—just driving less or keeping the lights off or other forms of emissions reduction—is no longer sufficient to solve the climate crisis,” Silver says. “We have to combine emissions reduction with carbon dioxide removal.”

Compost holds promise as a sequestration tool and offers a host of other benefits to boot. “This is one of those no-brainers that we should be doing anyway.”