|Howell T A,|
|Steiner J L,|
|Schneider A D,|
|Evett S R,|
Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 7, 1994
Publication Date: N/A
Interpretive Summary: Water use by irrigated winter wheat is important for irrigation management and for computer models. This paper summarizes daily and seasonal water use measurements by irrigated winter wheat grown in the Southern High Plains in a semi-arid climate. The water use was measured using large tanks of soil on scales called lysimeters. The mean water use of the wheat twas 893 mm (35 in) and the mean harvested grain yield was 505 g/m**2 (75 bu/ac). Water use coefficients, called crop coefficients in irrigation scheduling models, varied from 0.88 to 1.00 at peak ground cover for wheat during the three seasons. Other information was provided to be used in computer models for wheat growth simulation and for irrigation management models. The climatic regime in the Southern High Plains was shown to be an important factor in determining how well certain models would work in this environment.
Technical Abstract: Models of water use for irrigation scheduling and for crop growth simulation require validation of the evapotranspiration (ET) submodel. In this study, ET was measured for irrigated winter wheat (Triticum aestivum L.) at Bushland, Texas, in the semi-arid Southern High Plains for the 1989-90, 1991-92, and 1992-93 winter wheat cropping seasons using weighing lysimeters that contained undisturbed monoliths 3 m by 3 m by 2.3 m deep o Pullman clay loam soil (Torrertic Paleustolls). Weather data from a nearby station were used to compute daily ET values for a reference alfalfa crop (hypothetical) using the ASCE Manual No. 70 equations based on the Penman-Monteith equation and several other widely used "potential" or "maximum" ET models. Linear regressions between ET estimated from widely used equations and the reference alfalfa ET equation indicated that direct comparisons with computed ET values could not be reliably predicted with simple ratios. For the computed reference alfalfa ET base, peak basal cro coefficients (Kcb) varied from 0.88 to 1.00 for the three seasons and were lower than those reported from other locations. Peak mean corp coefficients (Kc) varied from 0.83 to 0.94 for the three seasons. Seasonal ET varied from 786 to 957 mm for the three seasons. ET and crop coefficients for winter wheat varied considerably with season.