Manure storage and handling techniques must continue to change to meet California's 40 percent dairy manure methane reduction goal and combat climate change, according to new research. After what is being called the most thorough measurement of the state's "whole-dairy" methane emissions, scientists confirmed that manure methane emissions come primarily from wet storage of manure.
"Until now relatively little research has been done to measure and pinpoint specific sources of methane emissions at dairies in California," said Michael Boccadoro, executive director of Dairy Cares, an agricultural sustainability advocacy group. "It is important that we base our strategies on sound scientific measurements from California dairies, and not just on studies conducted in other states."
In the study spearheaded by the Environmental Defense Fund (EDF) and the Dairy Cares coalition, scientists employed a variety of techniques to measure methane emissions at two Central Valley dairies. Data remained consistently similar, regardless of whether instruments were mounted in the ground or deployed in air craft or vehicles, researchers said.
"This important work advances our understanding in two areas - how to accurately measure and estimate methane emissions from California, and how to control them," said Josette Lewis, associate vice president of sustainable agriculture at EDF. "This helps ensure our strategies for reducing these emissions remain on target, and that we can accurately assess our progress."
The research was conducted by a team consisting of scientists from USDA's Agricultural Research Service, Penn State University, University of California - Davis and Aerodyne Research Inc. Claudia Arndt, a postdoctoral fellow at the Tropical Agricultural Research and Higher Education Center, led the team.
"We attributed much of the difference in emissions between dairies to the proportion of manure stored in liquid form," Arndt said. "This suggests that reducing the amount of manure stored in that manner, or the length of time manure is stored in liquid form, could significantly reduce methane emissions."
Additionally, the group found that direct emissions from ruminating animals tend to remain steady year-round. But emissions from manure storage can be highly variable and weather dependent - up to six times higher in the summer as compared to winter.
"This information is critical as the dairy community works with our partners, including EDF, the California Air Resources Board, the California Department of Food and Agriculture and technology providers to reduce emissions in a cost-effective manner," Boccadoro said. "Dairy Cares has always supported strong science to guide farmers in their efforts to improve environmental outcomes, and this research suggests the current strategies are right on target."
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Dairy methane emissions contribute up to 5 percent of the state's carbon footprint. A California law passed in 2016 set the goal for a 40 percent reduction of methane emissions from dairy manure by 2030.
The study confirms that state incentive programs to reduce methane emissions from liquid manure storage are right on track. So far, California has provided $260 million for dairy methane-reducing projects including digesters, which capture methane and convert it to clean renewable energy and fuel. The state is expected to have 100 to 120 dairy digesters operating in the next five years. The Alternative Manure Management Program has awarded funding to 58 California dairy farms to employ technologies and strategies that will reduce the amount of manure solids stored in wet conditions.
Studies are under way to measure changes in emissions on dairies where methane reduction measures have been installed. Ongoing research continues to verify and quantify how technologies can reduce methane emissions while improving overall air and water quality.
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