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salt discharges for various crops and irrigation techniques would be impractical. Thus the tax approach is shown as a hypothetical alternative to ~ ~ t- W the other strategies. The estimated response to a salt tax is approached indirectly. The salt constraint in the linear program was reduced parametrically to show changes in the optimal solution. The shadow price on a ton of salt discharge is equivalent to the effluent tax which would optimize salt discharges at each level of pollution by charging the full value of the right to put salt into the river. These effluent tax change points are shown in-the first column of part B of table 2. A tax as low as 50 cents per ton of salt could discourage over 40,000 tons of salt discharge. In the $4.50 to $5.50 range, the use of short sets and gated pipe with manual cutback would allow savings in salt loads of up to 90,000 tons. Additional reductions would be gained with taxes around $7.00, $11.00 and $13.00 per ton. The net social cost for any level of reduction in salt discharges beyond the first increment is much less than for irrigation system subsidies. However, a marginal tax rate which is less than even our revised estimate of downstream marg ina1 damages avoided drives net rents into negative territory. . ...-_. ~------- I. I , l"i3:::';~ I . I The results in part B of table 2 should be interpreted with caution. More extreme changes in farming practices might occur beyond the levels constrained by the model. As the salt tax increases, strong incentives might be exerted to replace unprofitable crops (i.e., barley and pasture) with higher valued crops (i.e., corn and pinto beans). Retiring the most marginally productive lands might also occur. Economic motives would also hasten the adoption of more efficient means of control 1 ing salt discharges. Thus total salt discharges 12