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<br />Water and Salt 8udaets. Water applications and salt discharge are based <br />on the detailed water budgets of Leathers and Young, updated by interviews with <br />.;.. soil Conservation Service and Agricultural Research Service special ists. Deep <br />~ <br />1-' percolation was .lowered to a leaching fraction of no less than 10:: of root zone <br />o <br /> <br />additions. <br /> <br />Zero deep percolation is both unattainable in the field and <br /> <br />undesirable due to eventual salt accumulation in the soil. <br /> <br />The contribution to Colorado River salt load per acre of crop activity is <br />found by multiplying deep percolation and seepage by the amount of salt found <br />in an acre-foot of subsurface water displaced into the river. This is <br />estimated by SCS personnel to be five tons of salt per acre-foot of drainage <br /> <br />water. <br /> <br />Due to limited research resources, the analysis assumed soil <br /> <br />productivity and aquifer characteristics to be homogeneous throughout the study <br /> <br />area. <br /> <br />Cost-Effectiveness of Irrigation Options <br />The cost per ton of reducing salt discharges for each crop under different <br />technological options was calculated by dividing the difference in returns to a <br />given crop under each irrigation option and the baseline earthen ditch method <br />by the corresponding difference in salt discharge (table 1). For all crops, <br />cablegation is by far the least-cost way of controlling salt discharges <br />(assuming no land levelling). Gated pipe with manual cutback is somewhat more <br />expensive, closely followed by irrigation from earthen ditches with short sets. <br />Land retirement of pasture, barley, and alfalfa is feasible where crop <br />rotations permit. <br /> <br />9 <br />