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<br />Amount of Salts <br /> <br />Fifty three percent of the annual salt load of 74,300 tons from <br />Moapa Valley comes from the springs in Upper Moapa Valley. An increase <br />of 3,000 tons of salt in the Upper Valley results from irrigation, <br />addition of saline ground water and erosion. Salt loading increases <br />in the Narrows from natural sources. <br /> <br />Surface flow from Lower Moapa Valley carries 17,100 tons of salt <br />annually and ground water carries 56,300 tons. <br /> <br />Control Potential <br /> <br />Control of salts is limited to those entering the river system <br />from irrigation and accelerated erosion due to man's activities. Control <br />of naturally caused salt loading does not appear to be economically <br />feasible. <br /> <br />Onfarm - Improved water management can minimize deep percolation of <br />irrigation water which is not beneficial to crop production. Optimum <br />crop production using saline water requires some deep percolation to leach <br />salts below the root zone. <br /> <br />The present application of water to irrigated lands in Lower Moapa <br />Valley results in 6,300 acre-feet of water percolating below the crop <br />root 'zone. This water mixes with the ground water and carries 21,300 tons <br />of salt downstream. Average irrigation efficiency is 45 percent. More <br />efficient application of irrigation water can reduce deep percolation and <br />surface runoff. Flexible scheduling and uniform applications of smaller <br />amounts of water are needed to attain higher irrigation efficiencies. <br />Inefficient water application has resulted from a lack of available <br />technical information and the high cost associated with increased <br />labor requirements for more efficient irrigation. Through the use of <br />semi automated irrigation systems improved water application would be <br />feasible. <br /> <br />Techniques for irrigation automation include clock controlled water <br />control gates and valves, and water measuring devices. Such methods <br />reduce labor requirements. Moisture and salinity monitoring devices <br />also enhance management of an irrigation system. <br /> <br />Increased crop yields and labor savings do not provide sufficient <br />economic returns to motivate installation by the land owners. Variations <br />in market prices for low value crops and inflating production costs <br />discourage the substantial investments required for automating irrigation. <br />Cost-sharing assistance for onfarm improvement of irrigation systems is <br />needed to accomplish reduction of downstream salinity damages. <br /> <br />Off-Farm - Improvements of the irrigation delivery system further <br />enhances benefits attainable with improved onfarm irrigation systems. <br />In Upper Moapa Valley, some modifications of the five delivery systems <br /> <br />0027~9 <br /> <br />29 <br />