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Managing Soil for Resilient Farmland

Managing Soil for Resilient Farmland

An Interview with Whendee Silver

Whendee Silver is a scientist and environmental educator in California. She earned her MS for Forest Science at Yale School of Forestry and Environmental Studies in 1987 and got her PhD in Ecosystem Ecology from Yale University in 1992. Silver is on the faculty at UC Berkeley, teaching Ecosystem Ecology.

Carbon sequestration is a natural process that can be affected by human activity. Silver explains how different land management strategies can impact the soil quality, including its carbon sequestration, as well as its nitrogen content.

Douglas Gayeton: How can human intervention increase the efficiency of grass landscapes that naturally sequester carbon?

Whendee Silver: The way we manage grassland doesn’t necessarily sequester carbon. most of the grasslands globally are grazed and a lot of grasslands are overgrazed. When overgrazing happens, those ecosystems lose carbon to the atmosphere.

Along with grazing practices, we’re also look at other approaches to bring carbon back into the landscape. Focusing on the waste stream looks very promising. Composting things like our food waste, green waste, and animal waste allows for a slow breakdown.

Composting that waste back into the land can sequester the carbon. Our results are suggesting that in California this has tremendous potential to take carbon out of the atmosphere, while also decreasing waste.

Ranchers and agriculturalists have been using organic amendments and organic waste products as a slow release organic fertilizer for a long time. We got away from that in the United States when we started using just commercial chemical fertilizers that release very quickly. While these chemicals can definitely increase the rates of plant growth, they also tend to increase the greenhouse gas emission into the atmosphere, which contributes to climate change.

The nice thing about using organic waste products is that they break down slowly. This gives the plant a chance to utilize more of those nutrients, while material’s carbon has a chance to get incorporated into the soil before it’s consumed by the soil’s microorganisms and released back to the atmosphere. Slowly the whole process down means that more carbon gets trapped in the ecosystem and it’s more beneficial to the atmosphere in the long run.

Douglas Gayeton: Could you define “carbon sequestration” and “soil carbon pool”?

Whendee Silver: “Soil carbon sequestration” is the storage of carbon in the soil in addition to the carbon that’s already there. Sequestration generally refers to the added carbon or to the added value that you get from changing a land management practice to increase the storage of carbon in soil.

“Soil carbon pool” is the quantity of carbon in the soil. We measure this by find the concentration of carbon in the soils and multiplying it by the volume of soil to give us the total quantity of carbon.

Douglas Gayeton: In addition to carbon, what other nutrient cycles are involved in the rangeland systems of Marin County?

Whendee Silver: Nitrogen is a key nutrient for plant growth and in many of our ecosystems it’s a resource that’s limiting to plant growth. One of the reasons farmers and ranchers use nitrogen fertilizers is that there’s not enough nitrogen present.

The organic waste that we are using is relatively rich in nitrogen, but it’s in a complex form so it’s partially locked away by the rest of the organic material. When that gets out into the soil, it’s broken down by the microorganisms in the soil. They release it very slowly; so this process acts like slow release fertilizer. That’s really important because nitrogen fertilizers are sources of a very potent greenhouse gas, nitrous oxide. While organic waste and compost organic waste can also be sources of nitrous oxide, they’re generally of much lower source than nitrogen fertilizers.