Climate

Applying Compost To Soil Can Help Cut Carbon Pollution

CREDIT: AP Photo/Lisa Rathke

People stroll past a pile of organic products at Grow Compost of Vermont, Tuesday, June 17, 2014, in Moretown, Vt.

Applying compost to farmland, even once, increases the soil’s ability to store carbon, according to experiments conducted at a ranch in California.

As the San Francisco Chronicle reports, initial research conducted by UC Berkeley bio-geochemist Whendee Silver on a ranch in Marin County has found that, if compost were applied to 5 percent of California’s land used for livestock grazing, it could result in a year’s worth of emissions from farm and forestry industries being captured. Silver told the Chronicle that theoretically, if compost were applied to quarter of California’s grazing land, it would result in soil absorbtion of three-quarters of California’s annual emissions.

“We need to reduce our fossil fuel emissions — there’s just no way around that problem,” Silver told the Chronicle. “But this is one of the things that we can do that certainly can make a difference. It’s inexpensive, it’s low technology, it’s good land use, it solves multiple problems.”

The research looked at the effect of adding compost made from “green waste” — things like vegetable scraps, grass cuttings, and cow manure — to to the soil of the ranch. John Wick, who owns the ranch where the experiment was conducted, said adding compost has other benefits as well. Since the application, Wick has seen more native birds and plant life, and he says his grass is more resistant to drought. Adding compost to soil, and thus increasing the soil’s ability to store carbon, can help restore soils that have been degraded by years of grazing and poor soil management. This can help increase the soil’s productivity, making it more effective at growing crops.

There are multiple other benefits of adding compost to soil, too. Previous research has found that applying compost to crops results in plants that need 30 to 70 percent less irrigation to grow. Compost also helps provide plants the nutrients they need to grow, thus reducing the need for chemical fertilizers: applying compost on vegetable crops can reduce the need for fertilizers by 33 to 66 percent.

The results of the research are important, because agriculture is responsible for about 10 percent of the U.S.’s total greenhouse gas emissions and about 13 percent of global greenhouse gas emissions, so finding ways for agricultural soils to capture carbon could help offset the sector’s contribution to greenhouse gas emissions. The carbon-sequestering effect compost has on soil has been documented in experiments before: previous trials have found that carbon storage of soils that have been treated by compost increased by 6 to 40 tons of carbon per hectare (2.471 acres).

The act of composting — not just the final product’s application to grazed soils — has been tied to emissions reductions in the past. When vegetable scraps and other green waste is sent to a landfill — an anaerobic, or oxygen-free environment — it produces methane, a potent greenhouse gas. When it’s composted, it’s exposed to oxygen, and produces very little methane, making composting organic material a more climate-friendly choice.

Still, as the San Francisco Chronicle points out, applying compost to a substantial percentage of California’s grazing lands may not be practical, because compost isn’t produced on a large enough scale yet. Some cities, however, have started municipal composting programs: Seattle imposes fines for residents who throw away organic waste, rather than composting it, and San Francisco also requires residents to compost.