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<br />· GJ.L~n <br /> <br />. <br /> <br />. <br /> <br />A similar analysis comparing SCS-BC TR-21 alfalfa monthly coefficients to SCS-BC <br />monthly coefficients derived by Hill et aI., 1989, and Pochop and Burman was also <br />performed. The monthly coefficients derived in their studies are shown in Table 5. The <br />average monthly coefficient as calculated at the Colorado weather station and the <br />comparison is shown in Table 6. The results do not show a consistent overestimation or <br />underestimation, which indicates local calibration on a monthly basis is needed. <br /> <br />~ <br /> <br />. <br /> <br />Verify or Correct Consumotive Use Procedures on Alfalfa Short and Pasture Short. <br />Hill et aI., 1989, demonstrates that evapotranspiration does not stop on the day that <br />irrigation stops. Because the back-up engineering used to develop their cutoff flow and <br />cutoff dates is missing, it is unknown if the USBR assumes that ET stops on the day the <br />irrigation stops. The ET procedure on the shortage acreage should inClude some method <br />for accounting for the ET of irrigation water that occurs after irrigation ceases. In the <br />reference crop ET procedure, the amount of ET that occurs as the soil moisture dries out <br />is accounted for. It is recommended that the USBR should preform some site specific <br />studies to verify or correct their ET procedure on alfalfa short and pasture short areas. <br /> <br />. <br /> <br />. <br /> <br />~ <br /> <br />. <br /> <br />Include Contribution of Stored Soil Moisture. The USBR's term NIB is equal to crop <br />consumptive use minus effective precipitation. SCS 1970 defines Consumptive Irrigation <br />Requirement (CIR) as "the depth of irrigation water, exclusive of precipitation, stored soil <br />moisture or ground water that is required consumptively for crop production." NIR does <br />not include any contribution from stored soil moisture or groundwater. The inclusion of <br />contribution to crop ET from groundwater by the plants is not recommended for several <br />reasons. The primary reason is that the source of the groundwater that is consumed in all <br />probability is deep percolation of irrigation water; therefore, indirectly it is accounted for <br />in NIR. Another reason is that the ET of groundwater probably occurs only in small <br />localized areas. Additionally, the task of determining groundwater ET could be very <br />burdensome as the basic data required to determine it is probably not available. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />It is recommended that in their calculation of NIR the USBR should include the <br />contribution from stored soil moisture, particularly the soil moisture that is stored as a <br /> <br />11 <br /> <br />. <br />