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<br />c;:) <br />CJ <br />to,) <br />....t <br />N <br />a.l <br /> <br />by personal interviews with 98 farmers, or 28 percent <br />of commercial crop farmers in the study area. The <br />models form a valley.wide characterization of farm <br />sizes, resource levels, cropping patterns and irrigation <br />practices. Measures designed to reduce salt pickup are <br />analyzed in the model by introducing proceases with <br />varying water supplies, application rates, timing or <br />irrigation methods. <br /> <br />The linear program is a conventional short.run <br />land and water allocation model with constraints on <br />cropland, water and acreages of specified crops. The <br />objective function is net return (defined as gross crop <br />sales minus operating costs). Each crop production <br />activity includes a coefficient representing annual <br />deep percolation per acre. The model is solved to find <br />the net income.maximizing situation for each of a <br />number of constraints on deep percolation losses. It is <br />assumed tbat salt is picked up at the rate of 5 tons of <br />dissolved solids per acre foot of deep percolating <br />water. This rate represents an average for the valley <br />and reflects a compromise among conflicting esti. <br />mates. <br /> <br />It could not be conclusively established that crop <br />yields would be adversely affected by the more <br />efficient irrigation practices, so no such cost is <br />included. The 15 percent of the acreage in deciduous <br />fruit orchards and other specialty crops are omitted <br />from the analysis reported here. Net income losses <br />due to hypothesized imposition of discharge standards <br />are computed. <br /> <br />Results <br /> <br />Some of the more important results of the <br />analysis are summarized in Table 27. The initial <br />solution or "bench mark condition" with respect to salt <br />pickup, net crop income, and irrigation water applied <br />to crops is reported in part A. From the results <br />summarized in part B, given our assumptions, it is <br />readily apparent that improved irrigation efficiency <br />can inexpensively hring about substantial reductions <br />in that portion of salt pickup due to on.farm irrigation. <br />The model indicates that about 80 percent of the initial <br />salt load in return flows due to percolation from fields <br />can be avoided at an incremental cost of less than <br />$2.20 per ton. <br /> <br />The results of crop substitution on salt pickup, <br />summarized in part C, show appreciably higher <br />estimated costs. Only about 40 percent of the initial <br />salt load can be removed, and the incremental cost <br />exceeds $60 per ton at that level of removal. By <br />comparison, recent cost estimates of control by canal <br />lining in the Grand Valley range from $14 to $100 per <br />ton. Program benefits (present downstream damages <br />avoided) are summarized elsewhere in this report. <br /> <br />No detailed study of the important issues <br />concerning the incidence of control costs or the <br />mechanisms for financing abatement programs was <br />undertaken. In generallties, the costs estimated here <br />of crop substitution and mucb of those for changing <br />irrigation practices would be borne by farmers <br />themselves. Some portion (up to 75 percent) of tbe <br /> <br />Table '7. Consequences of implementing on.farm, <br />nonstructural salinity controu. in the <br />Grand Valley: Selected results of the <br />linear programming model <br /> <br />Sail <br />Discharge <br />in Irrigation <br />Return Flows <br /> <br />Irrigation <br />Water <br />Requirementa <br /> <br />Incremental <br />Direct <br />Cost of Salt <br />Removal <br /> <br />Tutal <br />Net Farm <br />Income <br /> <br />-TONS.. -$.. ..Acre Feet- ..$ Per Ton- <br />A. Initial Condition (Both Cases) <br />146,510 5,962,301 214,745 <br />B. Case I, More Efficient Irrigation Practices <br />Adopted: <br />137,500 5,949,651 212,469 <br />100,000 5,897,019 202,995 <br />75,000 5,858,839 196,177 <br />50,000 5,807,160 180,015 <br />37,500 5,779,383 170,015 <br />C. Case II, Modification of the Cropping <br />Pattern : <br />5,797.679 <br />5,563,304 <br />4,854,002 <br />4,014,064 <br /> <br />1.40 <br />\.40 <br />1.53 <br />2.G7 <br />2.22 <br /> <br />125,000 <br />112,500 <br />100,000 <br />87,500 <br /> <br />219,012 <br />221,185 <br />227,348 <br />232,673 <br /> <br />7.65 <br />18.75 <br />56.74 <br />67.20 <br /> <br />aIncludes crop consumptive use, on.farm losses, and' <br />system delivery losses. <br /> <br />cost of changing irrigation systems can usually be <br />obtained through ASCS cost sharing programs. The <br />administrative and enforcement costs would be <br />absorbed by either the state or federal enforcement <br />agency. <br /> <br />ConelusloDs <br /> <br />Several limitations should be recognized in <br />interpreting this analysis. First, neither the amount of <br />drainage water associated with specified irrigation <br />practices nor the rate of salt pickup per unit of <br />drainage water are well established. In fact, <br />considerable disagreement is found on these points <br />among hydrology and soils specialists. Second, it may <br />not be possible to increase irrigation efficiency to the <br />degree assumed without some sacrifice in crop yield. <br />Finally, the regulatory and social costs of imposing <br />water quality standards have not been dealt with <br />where the effluent of individual irrigators is not <br />identifiable. Present water distribution policies in the <br />area' and Colorado water law do not provide any <br />incentive for reducing feturn flows, and relatively <br />drastic measures might be required to implement <br />nonstructural controls. These and other political! <br />administrative aspects remain to be studied. The <br />structural measures may be expensive, but they <br />would be relatively straightforward to implement <br />within present institutions. <br /> <br />Of the nonstructural control measures examined. <br />a sirilple modification in present irrigation practices <br />would apparently achieve a substantial reduction in <br />salt pickup at a cost relatively low in comparison to <br />other alternatives. However, this alternative might be <br />difficult and expensive to implement, monitor, and <br />administer. Substituting crops to avoid salt loading <br />would be more costly and limited in scope. <br /> <br />26 <br />