Research Report No. 213

Utah Agricultural Experiment Station Research Report No. 213
Verification of Trufgrass Evaportranspiration in Utah

Robert W. Hill
J. Burdette Barker

The continued competition for water in Utah necessitates accurate estimates of water needs and management requirements for legal water allocation as well as hydrologic considerations. Competition for water is due to increased urban and rural development as well as declining ground water levels and recurring drought conditions. This highlights the importance of careful water management including urban water conservation, particularly along the Wasatch front and in high growth areas of Utah. The majority of urban water use in the summer is from irrigation of landscaped areas, mostly turf. Thus, it is important to accurately estimate turfgrass water use to support water conservation efforts.


Previous statewide estimates of irrigated crop water use (evapotranspiration, or ET) in Utah relied on a combination of near state-of-the-art methodology (Penman type ET equation, 1982 Kimberly, ID version) at the time coupled with a calibrated Blaney-Criddle equation (Hill, 1994). A crop coefficient value for turfgrass ET of 0.56 was used with the 1982 Kimberly Modified Penman Combination alfalfa reference ET equation. This coefficient value was based on two years of data, as of 1993, from lysimeters installed in the Logan Golf and Country Club golf course. Ervin and Koski (1998), reporting a Colorado study, suggested that water could be conserved by irrigating turf every three days with a Kc of 0.7 (reference alfalfa, ETr, basis) for Kentucky bluegrass and 0.6 for turf type tall fescue. These coefficient values for fescue and bluegrass were about 7 to 25 % higher, respectively, than the Report # 145 value. This, plus other concerns, suggested that the coefficients derived from the Logan Golf and Country Club site in Cache Valley may not be applicable throughout Utah. Thus, site specific verification in a range of conditions was indicated to increase confidence in turfgrass water use estimates.

The originally anticipated product of this research was to determine verified crop coefficients, Kc, (Wright, 1982) for use with the 1982 Kimberly Penman ETr equation (Jensen, Burman and Allen, 1990) along with daily weather data to estimate near real time turfgrass water use in urban areas of Utah. However, subsequent to the initiation of this work, the American Society of Civil Engineers (ASCE) and the Irrigation Association adopted a “standardized” form of the Penman-Monteith ETr equation (Allen, et al., 2005). The desire among Utah’s state water agencies to use the “standardized” method provided an opportunity to calibrate it for use in estimating turfgrass consumptive use throughout Utah.

The primary purpose of this work was to verify turfgrass crop water use coefficients for use with either a grass reference ET (ET0) or an alfalfa reference (ETr) equation value. Specifically, the two main objectives were:

A. Study turfgrass water use by measurement with lysimeters including collection of sufficient weather data at each site for use with a Penman type combination reference ET equation.

B. Analysis of previously collected turfgrass irrigation and soil water content data at the BYU Agronomy Farm near Spanish Fork, Utah. Neutron probe and other data were collected during 1990 ? 1992 (or 1993, approximately) from the BYU turf plots. However, usable concurrent weather data, soil water measurements, and irrigation data were not obtained for any time period for these studies. Thus, this portion of the study, as included in the original proposal, was abandoned.

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