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<br />00 <br />r- <br />r..o <br /> <br />,-' <br />..- <br />.-- <br /> <br />-, <br />'--.' <br /> <br />Consumptive Use <br /> <br />Consumptive use, or evapotranspiration, is defined as the volume of <br /> <br />water used for vegetative growth in the transpiration and building of plant <br /> <br />tissue, plus the amount of water evaporated from plant foliage and ground <br /> <br />surfaces. <br /> <br />The climatological data used in the Jensen-Haise method of estimating <br /> <br />consumptive use were monthly average temperature and solar radiation recorded <br /> <br />at Walker Airfield near Grand Junction. <br /> <br />Consumptive use studies by various researchers indicate that during <br /> <br />recent years consumptive use ranges between 2.2 and 2.4 acre-feet per acre <br /> <br />during the irrigation season. During 1976, the crop-weighted irrigation <br /> <br />requirement for the Reed Wash study area was calculated to be 1.9 acre-feet <br /> <br />per acre (0.4 acre-feet per acre from precipitation). .This value has been <br /> <br />verified by lysimeter data (ARS, 1977) and cross checked by the Modified <br /> <br />Penman and Blaney-Criddle methods. <br /> <br />Tailwater <br /> <br />The ARS on-farm studies indicate the average tailw..ter runoff was about <br /> <br />43 percent of the field delivery (ARS, 1977). However, at the ARS intensive <br /> <br />study site where strict management was applied, a significant reduction was <br /> <br />accomplished with considerable expertise and more than usual labor to monitor <br /> <br />applications. Even though the tailwater runoff is relatively large, the <br /> <br />chemical analysis of the tailwater showed no significant difference.in <br /> <br />electrical conductivity or chloride concentrations from those in the <br /> <br />delivered irrigation water. <br /> <br />17 <br />