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<br />o <br />~ <br /> <br />(,...... Water and Salt Budc:ets. Water applications and salt discharge are I:lasec: <br /> <br />on the deta11&d water budgets of Leathers and Young, updated by 1nterviews .ith <br /> <br /> <br />so11 Conservation Service and Agricultural Research Service spec141fsts. Deep <br /> <br />percolaticn was lowered to a leaching fraction of no less than lC: of rect zene <br /> <br />addftions. <br /> <br />Zero deep percolation 15 both unatt.ainable 1n the fteld and <br /> <br />undesirable due to eventual salt accumulation in the 5011. <br /> <br />The contribution to Colorado River salt load per acre of crop acttvit) 15 <br /> <br />found by multiplying deep percolation and seepage by the amount of salt found <br /> <br />1n an acre-foot of subsurface 'fIIater dfsl=laced 1nto the river. <br /> <br />This 1s <br /> <br />estimated by SCS personnel to be five tons of salt per acre-foot of crainafje <br /> <br />water. <br /> <br />Due to lfmited research resources, the analysis assumec so11 <br /> <br />prOductivity and aquifer characteristics to be homogeneous throughout the study <br /> <br />area. <br /> <br />Cost-Effectiveness of Irrigation Options <br /> <br />The cost per ton of reducing salt discharges for each crop under different <br /> <br />technological options was calculated by dividing the difference in returns to a <br /> <br />given crop under each irrigation optfon and the baseline earthen ditch method <br /> <br />by the corresponding difference 1n salt discharge (table 1), For all crops. <br /> <br />cablegation is by far the least-cost way of controlling salt discharges <br /> <br />(assuming no lane levelling). Gated pipe with manual cutback is somewhat more <br /> <br />expensive, closely followad by irrigation from earthen ditches with short sets. <br /> <br />Land retirement of pasture, barlsy, and alfalfa is feasible where crop <br /> <br />rotations permit. <br /> <br />9 <br />