Presentations 2016

Fate of Nitrogen on California Dairies as Measured by Regulatory Reporting

University of California, Davis

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California is the largest dairy producer in the United States, generating over 20% of U.S. milk and cheese. Much of the California dairy herd lives in concentrated animal feeding operations (dairy CAFOs) in the Central Valley. Dairies also manage a significant amount of forage land, typically surrounding the CAFO, where animal waste is recycled. Through expansion and better production, the milk and manure output of Central Valley dairies increased nearly exponentially for five decades, until animal numbers levelled off in the 2000s. Since 2007, the dairy industry has been subject to new nonpoint source groundwater emission regulation in California. In the Central Valley, the dairy industry poses significant concerns for groundwater nitrate levels but also for groundwater salinization. We have digitized and are analyzing annual dairy reports submitted by individual operators to the regulatory agency (Regional Water Board) to assess the fate of nutrients on dairies in the Central Valley. In addition, we are able to assess data completeness and consistency, annual trends over the first eight years of the program, and evaluate the reporting program. Our analysis can be used to determine potential groundwater nitrate impacts based on field nitrogen mass balances.