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<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
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