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Massive Rangeland Carbon Sequestration Opportunities May Hinge on Urban Compost

by Warren Karlenzig

long-roots.jpg
There's carbon in them thar roots!

Just as San Francisco has made commercial and residential composting mandatory and other cities are considering doing so, a worldchanging application for using compost to dramatically increase carbon sequestration in suburban grasslands has been confirmed by the Marin Carbon Project.

Soil carbon sequestration is the process of moving greenhouse-gas causing CO2 from the atmosphere into the soil. After the ocean, soil is the second largest pool of carbon on the planet, with twice the amount of carbon that is in the atmosphere, according to Whendee Silver, a biogeochemist and professor at University of California at Berkeley.

"Healthy grasslands, which make up 30% of global land and 50% of land in California, put a lot of carbon into roots to lock in nutrients," Silver said. The Marin Carbon Project's research is focused on how to increase that natural carbon sequestering process, or restore it, in the case of damaged rangelands.

Silver and others presented the results of research last night that the Marin Carbon Project has been conducting at about two dozen sites in rural West Marin County, about 45 miles north of San Francisco.

The Marin Carbon Project is a collaborative research effort between the University of California, the USDA, the Marin Agricultural Land Trust and Marin Organic (the nation's first county-wide organic label) and The Nicasio Native Grass Ranch.

The project, which is about a year into a three to five-year process, has determined that an increase of 1 metric ton of carbon sequestration per hectare on 50% of California's managed rangelands could sequester 42 million additional metric tons (MMT) of carbon. This is slightly more than 41 MMT of carbon emissions from the California commercial and residential sector's energy use. This increase in carbon sequestration would also offset the 14 MMT of greenhouse gasses produced by livestock.

In order to make our grasslands and grazing lands better carbon sinks, Silver said, "we need to add compost and manure to the soils to help it sequester."

The Marin Carbon project has tested both manure and compost applications throughout dairy ranches, and while are both are effective at soil carbon enrichment, compost is preferred because it is less likely to contaminate land or watersheds, as improperly applied manure can.

Silver said researcher found that the ability of grassland soil to sequester carbon is not correlated with climate or soil type, but rather is directly related to how grasslands and rangelands are maintained. When trees and shrubs are left in grassland areas, for instance, there is 30% extra carbon sequestration.

Adding compost or manure also greatly increases soil carbon sequestration. "The test plots we added compost to retained over 90% of carbon that was added with no significant increase or methane or nitrogen oxides (two other potent greenhouse gases)." Tilling soil, on the other hand, has a negative impact on carbon sequestration, which doesn't bode well for industrial agriculture (which also uses petroleum based fertilizers as soils inputs) and corn-fed feedlot operations.

The test data from the Marin Carbon Project can now be applied to a more extensive life cycle and economic analyses. This means that other factors will have to be analyzed such as the total carbon produced by livestock, combined with the greenhouse gases that would have been produced if compost were sent to the landfill.

Other locations performing extensive soil carbon sequestration agricultural and rangeland research include New South Wales in Australia and Barritskov, Denmark.

Despite the lack of discussion in Copenhagen on agriculture and food production in relationship to climate change, the results are encouraging for combatting global change through specific actions in organic agriculture and sustainable food production that benefit regional economies.

San Francisco and other urban areas can use their food scraps to not only enrich their region's agriculture, grazing and dairy production--which strengthens the link between urban and rural food systems--but they can directly offset their carbon footprints. 

With the early results from the Marin Carbon Project in, metro-area greenbelts and farming lands now have even greater intrinsic value.

This makes the case even more for containing exurban sprawl around our cities and building smarter and denser communities. By all accounts, increasing protection and stewardship of regional natural resources has benefits that are far greater than most ever knew.

Warren Karlenzig is president of Common Current, an internationally active urban sustainability strategy consultancy. He is author of How Green is Your City? The SustainLane US City Rankings and a Fellow at the Post Carbon Institute.
      
 



This piece originally appeared on Green Flow

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Comments

The lack of increased methane and nitrous oxides after manure/compost application is interesting. This goes against current IPCC assumptions. However, the area is a difficult one, with conflicting results and it would be wrong to draw too many conclusions from one study.


Posted by: John Kazer on 5 Dec 09

i think the battle begins between burning our waste as energy and returning it as carbon stock to the soils? what will win out?


Posted by: shane on 2 Jan 10

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