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<br />. <br /> <br />water, diversions at Headgate Rock Dam, and flows in various parts <br />of the lateral system. <br />There are plans for future construction of two pump-back sta- <br />tions to pump drainage water from the Main Drain back into the canal <br />system. Such arrangements would be equivalent to an increase in <br />system efficiency of several percent, depending on the amount of <br />drain water recovered in this manner. <br />Onfarm Efficiency, The maximum attainable onfarm irrigation <br />efficiency on the Reservation under present conditions or under <br />conditions with onfarm improvements is not known. Some indication of <br />the potential for improvement of efficiency is indicated by studies on <br />the Wellton-Mohawk Irrigation and Drainage District [6], There the <br />onfarm irrigation efficiency was estimated to be 56 percent, and <br />various levels of efficiency improvement were considered, depending <br />upon the amount of onfarm improvements made under a cost sharing <br />program, and the extent to which efficient onfarm water management <br />is practiced in the District. Considering all pertinent factors, it was <br />concluded that onfarm efficiency of 72 percent was probably the high- <br />est that could be attained in that District in the near future, <br />Agricultural practices on the Colorado River Indian Reservation <br />are similar to the District. Consequently, it is assumed for purposes <br />of this report that the necessary 71 percent on farm (~~OO is <br />attainable on the Reservation, <br />Onfarm efficiency could be improved by greater precision in <br />irrigation scheduling, so that the amount of water applied during each <br />irrigation is matched to the needs of the crop, the character of the <br />soil, and the leaching requirements for Colorado River water. The <br />Bureau of Reclamation has a scheduling program called the Irrigation <br />Management Services OMS) Program. It relies on monitoring the soil <br />moisture in the field with a neutron probe, a combined nuclear and <br />electronic device that indicates moisture content directly, By keeping <br />a continual record of the moisture condition of each field or group of <br />fields, it is possible to predict the timing and amount of the next <br />irrigation. <br />An IMS program was begun on the Reservation in 1973 coopera- <br />tively among the Bureau of Reclamation, the Bureau of Indian Affairs, <br />26 <br />