Deficit Irrigation of Pastures Matt Yost, Clara Anderson, Niel Allen, Burdette Barker, Melanie Heaton, Justin Clawson, and Earl Creech
Introduction Deficit irrigation is any irrigation level that does not meet the crop’s full evapotranspiration (ET) demand, meaning evaporation from plant and soil surface and transpiration through plant growth. This strategy is often a last resort for optimizing water use as opposed to those that will not limit production. However, deficit irrigation is often necessary in parts of Utah due to drought or inadequate water supplies. This was especially true in 2021–2022 due to record droughts. Deficit irrigation strategies for pastures have been developed, but they have yet to be compared and evaluated in Utah. This fact sheet summarizes 6 years of research on deficit irrigation of pastures in northern and southern Utah. This research included different periods of irrigation, short-season irrigation, nitrogen fertilizer additions, and different pasture grass species to evaluate how they influenced forage production.
Study Methods Research Site Descriptions
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Nitrogen fertilizer did not increase the ability of grass to handle irrigation deficits in Lewiston, but results were in a single year, and more work is needed. Cache meadow brome and tall fescue in Panguitch responded similarly to deficit irrigation, and both are well adapted to the practice. Irrigation through June usually resulted in similar yield as later irrigations. Be sure to irrigate through June for deficit irrigation. Deficit irrigation may save between 6–16 inches of water per acre in evapotranspiration.
The deficit irrigation studies were conducted in Lewiston, Utah, from 2013–2018 and Panguitch, Utah, from 2016–2020. The Lewiston site, • located at the Utah State University (USU) Lewiston Pasture Research Farm (41°56'57"N, 111°52'16"W), has an elevation of 4,500 feet. The average annual precipitation is 18.5 inches, with the driest months being June through September. The soil texture is a fine sandy loam with a fluctuating water table that averages about 3 feet below the ground surface. The Panguitch site, located at the USU Panguitch Research Farm (37°52'6"N, 112°26'12"W), has an elevation of 6,550 feet. The average annual precipitation is 9.7 inches, with most of the precipitation occurring in July through October. The soil texture is a loam with a deep (> 15 feet) water table and a few gravelly bands. 1