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<br />21 <br /> <br />o <br />"'-J <br />Ul <br />N <br /> <br />Subroutine ACUS <br /> <br />Vegetation is capable of transpiring at its potential rate only <br /> <br />when the soil moisture storage is adequate. Consequently, the actual <br /> <br />rate of consumptive use is an adjustment to the potential rate based <br /> <br />on considerations of root zone storage, root zone depth, and root zone <br /> <br />supply. Due to the complexity of Subroutine ACUS, a simplified flow- <br /> <br />chart is shown in Fig. 5. The definition of variables is listed in <br /> <br />Appendix A. <br /> <br />Irrigated crops <br /> <br />The assumption has been made that aU irrigation water is <br /> <br />applied to the land use classifications Al through A18 in Table 3 and <br /> <br />consequently, the only water use from the root zone is transpiration <br /> <br />from the crops and evaporation from the soil surface. <br /> <br />From the <br /> <br />evalu1l:tion of crop"llcl_soiLcharacteristics, a value for root zone <br /> <br />depth and soil moisture storage capacity was determined in order th!':t <br /> <br />it would not be necessary to determine a root zone budget for each <br /> <br />;::_op. The total potential consumptive use is compared to the total <br /> <br />root zone supply from irrigation and precipitation. Three alternatives <br /> <br />can occur: <br /> <br />(1) If the root zone supply is insufficient to meet potential use <br /> <br />rate demands but ample water is stored within the root <br /> <br />/', i i <br />zone to meet this requirement, the actual consumptive use <br /> <br />:, <br />