From Waste to Wonder: Using Compost to Restore Carbon to Soil

By Nicole Block, Climate Communications Student Writer 

Carbon is one of the building blocks of life on Earth, but when carbon dioxide builds up in the atmosphere, it threatens life as we know it. UC Berkeley Climate Champion and professor of ecosystem ecology and biogeochemistry, Whendee Silver, is researching a solution to offset the 15 million metric tons of carbon dioxide emitted each year from cattle. She is using compost to help remove carbon dioxide from the atmosphere while also revitalizing grasslands and farmlands. Whendee Silver smiles while standing next to compost and recycling bins indoors

Compost is made up of decomposing biodegradable materials that come from plants and animals. When food scraps, grass clippings, and manure are composted and applied to grasslands–as opposed to dumped in a landfill–they become tools to lower carbon dioxide and other greenhouse gas emissions while helping farmers improve their soil quality to grow more food or grass to sustain livestock.

While many farming practices like tilling, driving tractors and manure management emit greenhouse gases into the atmosphere, there is a process that naturally stores carbon in the soil. Soil carbon sequestration is the process of capturing carbon from the air mostly through plant photosynthesis. This process provides nutrients for the soil while reducing the amount of carbon dioxide in the atmosphere.

When compost is added to soil, it contributes to this process. However, when organic material is instead placed in a landfill, it will emit greenhouse gases like carbon dioxide and methane as a result of decomposing anaerobically (without oxygen).

Carbon-Conscious Farmers

Whendee works with the Marin Carbon Project, a group located in the San Francisco Bay Area that seeks to enhance carbon sequestration in rangeland, agricultural, and forest soils to improve farm productivity and local ecosystem health while mitigating climate change. This group of farmers, researchers, county and federal agencies, and nonprofits is optimistic that they can improve soil quality and offset carbon dioxide emissions produced by agriculture by putting compost on grasslands. 

The project started in 2007 when Silver was approached by a rancher who was concerned about the impacts of climate change on their lands. Preliminary research showed that dairy farms had more carbon in their soils than the surrounding grasslands because ranchers disposed of manure by spraying it on fields. When a colleague suggested trying compost, she was skeptical of how effective this method would be or how she would even be able to measure it.

A large compost pile next to green hills.

A compost pile for the Marin Carbon Project.

Photo courtesy of Whendee Silver

Compost piles are made up of organic waste, which includes manure, leaves, grass clippings, wood, and food waste like fruits, vegetables and egg shells. After several months, the materials decompose and become a nutrient-rich organic fertilizer.


“It was ranchers and land managers who first proposed using compost as a soil amendment to us,” said Whendee. “They had observed the benefits of using compost on their lands; we came along and measured the biogeochemistry and found the climate change benefits.”

For nine years now, Silver and her lab have been working with the Marin Carbon Project and they have found that applying composted organic waste to grasslands and rangelands does improve agricultural productivity and sustainability, while actively mitigating climate change.

Sharing Their Results

Grasslands cover 40% of California’s land area and over 30% of worldwide land area. They have the potential to store carbon in their soil, but most of them are depleted of their carbon and carbon-storing capabilities because of overuse. Overgrazing, erosion, fires, and various land management techniques can disturb the soil to the point that it can no longer absorb carbon.

Whendee’s research has since led to the implementation of spreading compost on several ranches in Marin County and beyond, and has become the model for a widely implemented carbon farming program. The first three sites, Stemple Creek Ranch, Straus Dairy, and Corda Ranch each underwent extensive baseline soil sampling and assessment of their land before applying compost to about 100 acres of each farm. About 4,000 cubic yards of compost was applied in total.

In Silver’s research, applying composted agricultural and green waste to these grasslands was able to sequester carbon at rate of 1 metric ton each year for three years. The fields treated with compost had higher forage production, water holding capacity, and fertility than the control groups. Ranchers received these significant benefits, as well as the perk of using a sustainable method that helps the environment.

With this data scaled to 25% of California’s grasslands, the carbon stored at this approach would be 21 million metric tons, more than offsetting carbon dioxide emissions from cattle or most of the 21.6 million metric tons from the commercial sector.

“We use our data and that of others to improve models,” Whendee said. “One modeling project is looking at how climate change scenarios might interact with soil carbon storage with and without compost across the state. Another modeling project is aimed at determining the full life cycle of waste from a greenhouse gas perspective.”

Test plot with compost applied to it versus control plot with none.

The field on the left was treated with compost while the control field on the right was not, illustrating that the organic materials applied to the grass promoted more growth. Photo courtesy of Whendee Silver.

“We should be doing this now”

Applying compost to grasslands holds great potential not just for farmlands, but also for other uninhabited lands that could restore carbon to the soil, reduce greenhouse gas emissions and efficiently dispose of green waste. Whendee has been working with students, staff and faculty to explore UC Berkeley’s options for reducing their carbon footprint, which could expand on the Marin Carbon Project model.

“There is tremendous potential for our campuses to do a better job capturing and composting organic waste (as well as reducing waste overall),” said Whendee. “This is likely to save us money, make the campuses more sustainable, contribute to zero waste goals, reduce food insecurity, all while helping to mitigate climate change. We should be doing this now.”