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News Release

U.S. Department of the Interior
U.S. Geological Survey

Release: May 21, 2002
William Bidlake
253-428-3600, ext. 2641

Fallowed-fields water use studied at Tule Lake refuge

Resource managers of northern California's Tule Lake National Wildlife Refuge have more water management information as a result of a study published today by the U.S. Geological Survey (USGS), in cooperation with the U.S. Fish and Wildlife Service (USFWS).

USFWS refuge managers needed information about a potentially useful technique called fallowing in which an agricultural field is not used for a growing season. Letting the field rest for a season may save water that would otherwise be taken up by growing crops.

The USGS studied the amount of water lost from fallowed fields by evapotranspiration, which includes evaporation of water from plants and soils, to help the USFWS estimate how much water could be conserved under typical fallowing scenarios. The USGS studied three fields on two fallowed lots that had been irrigated and planted to crops in 1999 and fallowed in 2000. A soil- protecting cover crop was planted in one fallowed field during 2000, and nothing was planted in the other two fields, although weeds and "volunteer" crop plants did grow in those fields during the study.

The study found that total evapotranspiration losses during May to October 2000 were almost equal among the three fields-about 17 inches. However, the study also found that differences among the fields in the timing of evapotranspiration losses were linked to differences in the timing of plant development, growth, and senescence (die-off) in each field. This linkage between evapotranspiration and vegetation points to the important role that vegetation plays in evapotranspiration losses.

"What we've learned in this study is a good start to finding ways to conserve water," said USGS hydrologist William Bidlake, author of the report. "We could look at ways to boost water conservation through such methods as the mowing or tilling of fallowed fields to suppress water-consuming vegetation."

The report, "Evapotranspiration from selected fallowed agricultural fields on the Tule Lake National Wildlife Refuge, California, during May to October 2000," by William R. Bidlake, is published as U.S. Geological Survey Water-Resources Investigations Report 02-4055. Copies of the report are available for reading at the U.S. Geological Survey, 1201 Pacific Avenue, Suite 600, Tacoma, WA 98402. Copies can be purchased from the U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225-0286, telephone 303-202-4200. The report can also be viewed on the Web at

The USGS, a bureau of the Department of the Interior, serves the nation by providing reliable scientific information to describe and understand the Earth; minimize loss of life and property from natural disasters; manage water, biological, energy, and mineral resources; and enhance and protect our quality of life.

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