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INTRODUCTION N c..:> .t::a. CJl salinity problems in the arid and semiarid areas of the United States Cu.s.) are a critical concern to those involved in the management of our natural resources. The salinity problem can take two forms. One is a salinity buildup in the soil root zone that reduces or precludeS an economic return from growing agricultural crops. The other is excessive salinity in ground- water, lakes, streams, and rivers that reduces or precludes their use for irrigation, domestic, municipal, and industrial water supply or for fish and wildlife habitat. Irrigation specialists agree that improved irrigation efficiency, in many circumstances, offers an effective approach towards reducing the contribution to salinity in river systems from irrigation. Frequently, it is the most cost effective option identified. The USDA has gained considerable experience in the Colorado River Basin Salinity Control Program during the past several years. Starting in about 1973, the U.S. Salinity Laboratory at Riverside, California, the U.S. water Conservation Laboratory at Phoenix, Arizona, and the Irrigation water Management Research ,unit in Fort Collins, ColoradO, have conducted field research and demonstration projects in this field. These were aimed directly at evaluating various existing options for increasing irrigation efficiency-- thus reducing the salt load in the return flow to the Colorado River--and to develop additional new technology. This work, supported in part with funds from the EPA and the USBR and complemented by work of the University of Arizona and Colorado state University, had a substantial impact on the' development of the technical assistance and cost-sharing programs of USDA. USDA has performed detailed studies in several high priority irrigated areas which are potential contributors to the salinity problem of the Colorado River. These studies and the resulting reports quantify the salinity contribution from onfarm irrigation: recommend an implementation plan: and identify the costs, benefits, and effects of implementing the plan. Implementation of the first plan began in 1974 in the Well ton-Mohawk Drainage and Irrigation District in Arizona. Implementation in two additional units, the Grand Valley in Colorado and the Uinta Basin in Utah, is now underway. Initial implementation schedules are for 10-year periods but will be readjusted based on available resources. Backqround The Colorado River Basin encompasses portions of seven states: colorado, wyoming, Utah, Nevada, New Mexico, California, and Arizona. The river is 1,400 miles long, with its headwaters in wyoming and colorado. It empties into the Gulf of California and serves some 14.5 million people on its way. It is one of the most physically developed and regulated rivers in the Nation. In 1964, the waters were totally consumed and flows no longer reached the Gulf of california. The river flow is apportioned among Upper and Lower Basin States and the Republic of Mexico. There are some 2.6 million acres of private irrigated 3