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Economic Damages to Irrigated Agriculture 27 N c:.-, "" .....1 about 3.5 times higher than average damages in the 800-1100 mgIL range. Gardner comments that, "This higher estimate serves to illustrate the nonlinear nature of the salinity function, Salinity damages increase as salinity increases, . _ ." The regression formulas for yield vs. salinity are as follows, with coefficients rounded (y = yield; t=TDS in mgIL): Lettuce: y(cwtJacre) = 298.60 - 9.36(1O.2)t Alfalfa hay: y(tons/acre) = 9.34 - 2.39(1O-3)t Onions: y(cwtJacre) = 367.19 - 9.05(10-2)t Carrots: y(cwtJacre) = 681.56 - 0.4211 Orangesffangerines: y(cwt/acre) = 155.51 - 0.3511 + 2.09(10-2)t2 LemonslLimes: y( cwt/acre) = 191.09 - 8.46(1O-2)t Grapefruit: y( cwtfacre) = 561.42 - 0.5611 Table grapes: y(tons/acre) = 16,70 - 1.60 (1O-2)t No meaningful regression formula was obtained for avocado yield because of limited data. Computer Model Calculations of Agricultural Damages Data on yieldffDS relationships for the nine salt sensitive crops have been taken from the extrapolated regression curves and entered in the computer program input data. The com- puter program will display these TDS/yield relationships for each of the crops, and will per- mitthe user to modify these data if better data become available. The program also displays data on various geographic areas using Colorado River water for irrigation: Central Arizona Project, AZ Yuma County, AZ (includes Gila Project, Yuma Mesa, and Wellton-Mohawk Divisions) Imperial County, CA Riverside County, CA (includes Coachella Valley and Palo Verde Irrigation Districts) LaPaz County, AZ (includes Colorado River Indian Reservation) The program also includes a "Future Agricul- tural Area," i.e., a space for potential future expansion of the program. The program also permits any of the areas to be eliminated, e,g" the Central Arizona Project for those years before Colorado River water is delivered. The program displays, for each of the above listed areas, data on current and baseline TDS levels (as selected by the user), unit value of each crop, and acreage planted in eacb crop. The program permits eacb of these values to be updated as new data become available. Tbe program automatically calculates economic damages for each crop for each area, for various selected future years. For agricul- tural forecasts it is not expected that anyone can accurately forecast future crop acreages or future crop values. However, provision is made for sucb changes if desired by the user. Other- wise tbe current (1986) and future damages will be based on 1985 crop prices, on 1984 crop acrcages planted, and on the differential yields in crop between a forecasted TDS level (from Figures 3-5) and a selected baseline TDS level. The program does not take into account manage- ment practices, market impacts, or natural forces such as pests, floods, or drought. Other Agricultural Costs Related to Saline Irrigation Water The autbors of this report have attempted to obtain estimates of economic damages to agricul- ture, other than those resulting in decreases of crop yield. Tbese other forms of damage include: (a) loss of crop value because of removal of land from production as a result of salt build-up from irrigation with saline water; (b) costs of extraordinary agricultural prac- tices required to compensate for salinity, such as installing tile drains, cleaning drains, and adop- ing sucb farm practices as land levelling, sprinkler/drip irrigation, etc., when such adop- tion is due to salinity alone and not otber economic factors; (c) losses in crop production value due to necessary shifts fom non-tolerant higb-value crops to lower-valued salt -tolerant crops.