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o.DOU~" 2 Substantial programs have not been implemented to rejuvenate the irrigated lands in Colorado that have become degraded by salinity. Programs have been implemented to reduce salinization of the Colorado River with some success, but not of the Arkansas or South Platte Rivers. Some Guiding Principles of Salinity Control There is usually no "single-way" to achieve salinity control in irrigated lands and associated waters. Many different approaches and practices can be combined into satisfactory control systems; the appropriate combination depends upon economic, climatic, social, as well as edaphic and geohydrologic situations. However, some important principles and strategies of salinity management exist that should be understood and used to develop appropriate "packages" of management for purposes of increasing water use efficiency in irrigation, reducing the drainage discharges which cause waterlogging and soil/water salinization and optimizing the usability of irrigation water supplies. These principles and strategies will now be briefly reviewed in terms of four important management element-objectives; they are discussed more fully elsewhere2. 1. Deliver Water Uniformly to Fields in Correct Amounts and Timing A key element of salinity control is efficient irrigation. This requires that consumable water must be applied uniformly, without undue excess. to fields to provide the individual plants with water as needed to meet evapotranspiration requirements and to avoid salinity stress. Thus, careful control of irrigation timing, of application uniformity and of amount of water applied and stored in the rootzone are prerequisites in this regard. This calls, optimally, for water delivery to the field on demand, which, in turn, requires close coordination between the irrigator and the organization that delivers the water. It also calls for measurement of water flow <rates and volumes), feedback devices that measure the status of water and salinity in the soil, ways to predict or measure the content of available soil moisture, ways to detect or predict the onset of plant stress, and ways to control of volume delivered to each field and its distribution within it. It also calls for the prevention of seepage from the distribution and drainage-discharge canals. 2. Minimize Deep Percolation and the Need for Drainage To prevent the excessive accumulation of salt in the crop rootzone from irrigation, a relatively small amount of extra water (or rainfall) must, over the long term, be applied in excess of that needed for evapotranspiration (ET) and this excess must pass through the rootzone in a minimum net amount. This amount; in fractional terms, is referred to as the "Ieaching requirement" (L,., the fraction of infiltrated water that must pass through the rootzone to keep salinity within acceptable levels for crop production). In fields irrigated 2 Rhoades, J.D., A Kandiah, and AM. Mlshali. 1992. The Use of Saline Waters for Irrigation. FAO Irrigation and Drainage Paper No. 48, Food and Agricultural Organization of the United Nations, Rome, Italy and Rhoades, J.D. 1999. Use of saline drainage water for irrigation. Drainage Monograph, Amer. Soc. Agron. (in press). .