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<br />Amounts of Salts <br /> <br />Five percent of the average annual salt load from Virgin Valley to <br />Lake Mead is estimated to accrue, between the Littlefield and Riverside <br />stream gages, from excessive deep percolating irrigation water. The <br />remainder is mostly inflow from upstream. The application of water to <br />3,525 irrigated acres in Virgin Valley results in 19,000 acre-feet of <br />deep percolating water which mixes with ground water and carries salts <br />downstream. Surface flow from Virgin Valley carries 346,900 tons of <br />salt annually and ground water carries 76,100 tons for a total of <br />426,000 tons, <br /> <br />Control Potential <br /> <br />Control of salts is limited to those entering Virgin River from <br />irrigation. Control of salt loading from channel erosion and from <br />other natural causes is not economically feasible, <br /> <br />Onfarm - Improved water management efforts will minimize deep <br />percolation of irrigation water which is not beneficial to production <br />of crops, Optimum crop production with water containing salts requires <br />some deep percolation to leach salts below the root zone. <br /> <br />More efficient application of irrigation water can reduce deep <br />percolation and surface runoff. Flexible scheduling and uniform appli- <br />cations of smaller amounts of water are needed to attain higher irrigation <br />efficiencies. Inefficient water application has resulted from the high <br />cost associated with increased labor requirements for more efficient <br />irrigation. Improved water application can be achieved through the use <br />of sem1automated irrigation systems. <br /> <br />Techniques for irrigation automation include clock controlled <br />water control gates and valves, and water measuring devices. Semi auto- <br />mated systems reduce labor requirements, . Moisture and salinity monitoring <br />devices enhance management of an irrigation system, <br /> <br />Inventories of the irrigated land in Arizona show that 605 acres <br />are irrigated by sprinkler systems near Mesquite, 490 acres are sprinkled <br />and five acres are drip irrigated near Littlefield, There are no <br />sprinkler or drip irrigated lands in the Nevada portion of the study <br />area. Analyses of the sprinkler and drip systems were not made since SCS's <br />Irrigation Method Analyses Program (IRMA) assumes a present efficiency of <br />70 percent, This is greater than the efficiency of the surface systems. <br />The areas that are sprinkled receive pumped ground water that is better <br />quality than the surface water. <br /> <br />Increased crop yields and labor savings are not sufficient economic <br />returns to motivate installation of salinity control practices by the <br />landowners, Variations in market prices for low value crops and inflating <br />production costs discourage substantial investments required for automated <br />irrigation, Cost-sharing assistance for onfarm improvement of irrigation <br />systems is needed to accomplish reduction of downstream salinity damages, <br /> <br />33 <br /> <br />r ,I" r. 'r) .~ <br />,:'_ll.....1 <br />