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<br />feasible. <br /> <br />Five different crops were considered in conjunction with ten <br /> <br />~ <br />..,., <br />o <br />-..l <br /> <br />different combinations of irrigation technologies and management techniques. <br />The model maximizes annual net returns to the fixed resources. land and <br /> <br />water. <br /> <br />This measure is an appropriate social welfare indicator for the <br /> <br />producer case where supply impacts are not large enough to materially affect <br /> <br />commodity prices (Marglin. pp. 40-42). Returns are measured on a pre-tax basis <br /> <br /> <br />with no consideration of federal cOlMlodity programs. The model represents a <br /> <br /> <br />long-run planning horizon. because annualized irrigation improvement costs are <br /> <br />included as an important pol icy variable. The private costs imposed by an <br /> <br />abatement program are defined as reductions in annual net incomes (producer <br />rents) as compared with the baseline (no-program) case. <br /> <br />Model Cropping Assumption". Only the historically observed irrigated <br /> <br />field crops are incorporated into the model: <br /> <br />alfalfa hay. pasture. corn. <br /> <br />edible dry beans and barley. Perennial fruit crops. accounting for slightly <br />over 10lS of the irrigated acreage. are not simulated. Thus. about 50.000 of <br />the valley's estimated 56.000 irrigated acres are represented. The average <br />1977-81 crop mix on the 27.000 acres of lands served by the U.S. Bureau of <br /> <br />Reclamation irrigation project was assumed to be representative for the entire <br />valley. One standard deviation was added and subtracted from these averages to <br />provide upper and lower acreage limits for the model solutions (Miller). <br /> <br />The machinery complements and input use rates are adapted from crop <br /> <br />budgets developed by Leathers and Young and from Extension Service reports. <br /> <br /> <br />Crop prices were based on real five-year average prices received and. similar <br /> <br />to input prices. were expressed in 1982 dollars. The crop budgets represent <br /> <br />costs for the average size (150 acres) of a full-time farm unit in the Grand <br /> <br /> <br />Valley (U.S. Soil Conservation Service). Crop production is a secondary source <br /> <br />6 <br />