“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.”
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.”