California Institute for Water Resources
California Institute for Water Resources
California Institute for Water Resources
University of California
California Institute for Water Resources

Suitability of alfalfa for winter groundwater recharge


California’s groundwater has been stressed, most recently by hard-hitting drought. One proposed solution for recharging aquifer is agricultural groundwater banking. Using this approach, farmland is flooded during the rainy winter season to recharge the underlying groundwater. Optimizing agricultural groundwater banking for specific crops can be challenging. The main goal of this project was to better understand how alfalfa, which is grown year round, responds to winter flooding.


Helen E. Dahlke
Assistant Professor in Integrated Hydrologic Sciences
University of California, Davis

Project description:

Groundwater is a big issue in California. During the recent extended drought, the state passed the Sustainable Groundwater Management Act (SGMA), which requires the formation of groundwater agencies and sustainability plans. With this new legislation, it is even more important to develop new recharge technologies, including those that directly utilize irrigated agriculture and excess water to replenish groundwater.

Agricultural groundwater banking – an approach to groundwater recharge where farmland is flooded during California’s rainy winter season to recharge the underlying aquifer – is a promising technology. Using farmland for recharge and groundwater banking potentially provides a wide range of opportunities for long-term water security given the large irrigated acreage and water distribution infrastructure available in California. However, challenges and concerns remain regarding the effect that winter, on-farm flood flow capture could have on permanent cropping systems such as alfalfa.

The main goal of this research was to conduct field studies over two years to increase understanding of the response of alfalfa forage crops to winter water application for groundwater recharge. Specifically, as part of this project, Dr. Dahlke’s team conducted replicated field experiments on two commercial alfalfa fields and one field at the Kearney Agricultural Research and Education Center to test the effect of modest and high amounts of artificially applied winter water on growing season alfalfa yield. The study also considered the effect of fall dormancy rating on alfalfa response. In addition, the study assessed how winter water application affects growing season water balance and irrigation demand under different soils and climate conditions.

Jim Morris, land owner and study collaborator. Photo by Steve Orloff.
Winter flooding in alfalfa fields in Siskiyou County, CA. Photo by Steve Orloff.
Photo by Steve Orloff.

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