Climate Change and Agriculture

How can grazing and tilling reduce greenhouse gas emissions?

Differences in nitrous oxide emissions and nitrogen retention can increase the mitigation potential for greenhouse gas reduction in organic systems. Some processes can increase carbon storage in conventional, reduced tillage and no-tillage agricultural systems. Louise Jackson, professor emerita of land, air, and water resources anticipates climate change impacts on agricultural systems and compares ecosystem services across farmscapes and along gradients from intensive, irrigated agriculture to low input, grazed, upland systems in California.

 

What can we learn from historical water records to help predict irrigation needs?

Hydrologic modeling studies can evaluate the long-term impacts of climate change on crop water requirements, soil salinity and groundwater quality. Using historical water availability data, Jan Hopmans, professor of land, air, and water resources, applied a climate change model and sensitivity analysis to show that estimate crop evapotranspiration values are not likely to increase in California’s Central Valley because of the increasing atmospheric carbon dioxide concentrations. However, much uncertainty remains because of the large unknown heat tolerance for the wide range of crops grown in the Central Valley.

 

Can California offset greenhouse gas emissions through increasing carbon dioxide absorption by perennial crops?

Large information gaps exist concerning how much carbon might be sequestered by perennial crops in California, and how management practices for nitrogen fertilizers applied to orchards and vineyards can be utilized in a manner that would reduce nitrous oxide emissions. Researchers in the lab of David R. Smart, associate professor of viticulture and enology, work on several facets of this question, including turnover and decomposition of roots in vineyards and orchards, changes in emissions of carbon dioxide and nitrous oxide following fertilization and irrigation, and quantitative comparisons of carbon and nitrogen emissions in perennial crops with natural ecosystems. One overall objective is to determine how agricultural systems can be managed in ways that partner with State and Federal agencies in order to improve California air quality.

 

How will agriculture be a source and a sink for greenhouse gases under a changing climate?

Agricultural lands are going to be further depleted in soil carbon with global warming. Johan Six, assistant professor of plant sciences, and colleagues work to determine whether agricultural practices such as cover cropping, reducing fertilizers, manuring and conservation tillage are economically feasible practices to increase soil carbon and reduce the emissions of other greenhouse gas. They are integrating ecosystem models with economic models to help the state of California better understand how carbon trading might help energy suppliers comply with future reductions in greenhouse gas emissions.

 

How is projected climate change in California and internationally likely to affect economic prospects for California agriculture?

Dan Sumner, director of Agricultural Issues Center, expects many adjustments in California agriculture over the next several decades — climate change being only one. He observes that market effects caused by changes in supply and demand shifts outside of California may be more important than impact on production in California. California producers will seek comparative advantages by gradually adjusting what they produce, with some crops moving north and new crops introduced. Yields may decline or become more variable, but changes in price caused by climate change outside of California will affect what is produced and the income earned.

 

What is the effect of reduced tillage on greenhouse gas release and sequestration from agricultural fields?

Studies can determine if irrigated agricultural systems are a useful means of mitigating or “offsetting” greenhouse gas emissions. Kyaw Tha Paw U, professor of land, air, and water resources, and colleagues predict the effects of tillage on carbon sequestration in agricultural soils. Paw U has expertise in biometeorology, a branch of atmospheric science that studies the physical processes that govern exchanges between biological surfaces and the lower atmosphere. These exchanges include motion, heat and water vapor, and monitoring various gases from soils and plants in agricultural fields. He has monitored gases from fields that grow wheat, corn, sunflower and chick peas.

 

How do elevated carbon dioxide and ozone levels affect carbon and nutrient dynamics in agroecosystems?

According to research by Valerie Eviner, associate professor of plant sciences, and colleagues have found that elevated carbon dioxide and ozone can alter crop traits, which then alter nutrient and carbon dynamics. These changes in how carbon moves between the atmosphere and crops have the potential to alter long-term productivity and feedback to climate change.

 

What is sustainable agriculture and how is sustainable agriculture research and education adapting to climate change?

Details of sustainability differ from place to place. In California, the economic, environmental and social dimensions of agriculture, food, nutrition and health are interconnected. Leadership in California sustainability focuses on sophisticated science and methods in agriculture, not production of low-cost agricultural products. Thomas Tomich, professor of environmental science and policy, develops proof of concept in methods for improving land, air and water quality. Tomich directs the UC Agriculture and Natural Resources statewide Sustainable Agriculture Research and Education Program (SAREP) and is the founding director of the Agricultural Sustainability Institute.

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