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2347 Irrigation on the Reservation presently flushes some salts from beneath the surface, but water use by natural vegetation on the flood plain appears to cause salt retention in a far greater amount. The net result is that the Reservation is not a contributor of salt to the river. It is estimated that at present the Reservation discharges about 80,000 tons less salt to the river than are contained in surface diversions and subsurface inflow to the Reservation. This estimate is derived from 1974 diversions of about 649 ,000 acre~feet of water containing about 692,000 tons of salt. Irrigated agriculture is quite profitable on the Reservation, and for this reason expansion of irrigated land on the flood plain is anticipated in the foreseeable future. Ultimate development of 93,046 acres of irrigable land on the flood plain is anticipated to be complete by 1994. Because the water supply is limited, this must be accom- panied by a substantial improvement in water use efficiency. This will require structural improvements to the water distribution system (i. e., lateral lining), and improvement of onfarm irrigation effiCiency to at least 71 percent. Even with ultimate development approximately 18,700 acres of natural vegetation would remain, much of which is expected to continue to retain salt for another century or more. Under those conditions, it is estimated that between 60,000 and 80,000 tons of salt will continue to be retained on the Reservation each year for the next two decades. Farther in the future the Reservation will probably approach salt balance. Plans have been formulated for measures to improve water use efficiency on the Reservation. The Bureau of Indian Affairs has planned a program of irrigation system improvements to reduce canal and lateral seepage losses, and operational spills from the system. A voluntary Irrigation Management Services program was initiated in 1973 to assist farm operators to irrigate more efficiently, and the ultimate goal is to attract all farm operators into the program. Because of the economic incentives to develop additional irrigable land, and the necessity of attaining an onfarm efficiency of 71 per~ cent, the general objectives of the Federal salinity control program 3