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Deficit irrigation of alfalfa as a strategy for providing water for nonagricultural uses




Hanson, Blaine, author
Putnam, Dan, author
Snyder, Rick, author
U.S. Committee on Irrigation and Drainage, publisher

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Alfalfa is California's single largest agricultural water user due to its large acreage and long growing season, using 4 to 5.5 million acre feet of water each year. Because of this water use, the California Department of Water Resources is interested in deficit irrigation of alfalfa for providing water for transfer elsewhere. One strategy is to terminate irrigation during July and August when alfalfa yields are relatively small and use the "saved" water for nonagricultural uses. The amount of transferable water would be the difference in the evapotranspiration (ETc) of a fully-irrigated field and that of a deficit-irrigated field; however, no information exists on the potential ETc differences. Evapotranspiration was determined in a commercial field using the eddy covariance and surface renewal energy balance methods in a fully-irrigated part of the field, and the surface renewal method in the deficit irrigated part of the field. In addition, alfalfa yield, applied water, canopy coverage and plant height measurements were made in both parts of the field. Deficit irrigation greatly reduce alfalfa yield in 2003, 2004, and 2005. Yield reductions due to deficit irrigation generally ranged from 41 to 88% of the fully-irrigated treatments. Cumulative ETc in 2005 was 48.1 inches for the fully-irrigated treatment. Deficit irrigation (no irrigation) started on July 25. Cumulative ETc between July 25 and December 6 (end of measurement period) was 20.8 inches for the fully irrigated treatment and 11.4 inches for the deficit irrigated treatment for a difference of 9.4 inches.


Presented at Ground water and surface water under stress: competition, interaction, solutions: a USCID water management conference on October 25-28, 2006 in Boise, Idaho.

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