Rangeland covers more than half of California’s land mass. Our rangelands provide a multitude of beneficial uses, including livestock grazing and wildlife habitat. They can also be significant carbon sinks.
New research from UC Berkeley suggests rangeland management practices that could increase the ability of these lands to store atmospheric carbon, our primary greenhouse gas. Dr. Whendee Silver and graduate student, Rebecca Ryals, reviewed the potential carbon storage and forage benefits of compost application to rangelands in their recently published paper in the Ecological Society of America.
The researchers looked at two distinct California grassland types, one near the coast in Marin County and the other in Brown Valley in the Sierra foothills. At the beginning of the three-year study, they applied one surface dressing of commercially available composted organic green waste to their experimental plots at a rate of about 5 pounds of dry matter per square foot (approximately one-half an inch thick). Cattle were grazed in the spring and fall for up four weeks while there was sufficient forage. They took weekly measurements of soil emissions of the greenhouse gases carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). The researchers collected soil samples at the end of each growing season to analyze for carbon content. They also measured the above and belowground biomass at its peak growth to determine changes in grassland productivity. The data were used to calculate net change in carbon storage.
The study found that the addition of compost did not change the soil emissions of N2O or CH4,and though CO2 emissions increased they were offset by gains in grassland productivity. In five of the six research plots, net ecosystem carbon storage was increased when compost was present, and was sustained over the three-year period. Importantly, the sixth plot with decreased carbon storage compared to the control also had lower soil moisture, indicating that compost applications may be most effective for increasing carbon sequestration in wetter regions.
This research will be helpful as ranchers, their allies and policymakers grapple with identifying rangeland management practices that can reduce GHGs and sequester carbon in soil. It will be useful in conducting full life cycle analyses that take into account additional factors outside the scope of the study, including the GHG emissions associated with compost production prior to application on rangelands and the emissions related to the transport of compost to grazing lands. The economic feasibility of widespread application of compost on rangelands will also need to be evaluated to determine the degree to which the practice will be applicable in commercial operations.