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<br />.' <br /> <br />0:00062 <br /> <br />6 <br /> <br />4. Monitor Soil Salinity to Evaluate Irrigation/Drainage Appropriateness <br /> <br />For reasons given elsewhere4, I conclude that the effectiveness of irrigation/drainage <br />design and management and of water-table/salinity control can not be achieved using <br />traditional leaching requirement and salt balance concepts. Direct monitoring of rootzone <br />salinity levels and distributions across fields needs to be undertaken periodically in order <br />to evaluate the effectiveness of salinity, irrigation and drainage management programs, <br />especially those involving drainage water reuse. <br /> <br />Indeed, in my opinion, the proper management of soil and water salinity requires the <br />following: I) an adequate knowledge of the level, extent, magnitude and distribution of <br />rootzone soil salinity in the fields of the irrigation project (a suitable inventory of <br />conditions); 2) the ability to be able to detect changes and trends in the status of soil <br />salinity over time and the ability to determine the impact of management changes upon <br />the conditions (a suitable monitoring program); 3) the ability to identify salinity problems <br />and their underlying/inherent causes, both natural and management-induced (a suitable <br />means of detecting & diagnosing problems and identifying their causes); 4) a means to <br />evaluate the adequacy and effectiveness of on-going irrigation and drainage systems, <br />operations and practices with respect to controlling soil salinity, conserving water <br />supplies and protecting water quality from e){cessive salinization (a suitable mean~ of <br />evaluating management practices), and 5) the ability to determine the areas in fields and <br />in irrigation projects where excessive deep percolation is occurring, i.e., where the water- <br />and salt-loading contributions to the underlying groundwater are coming from (a suitable <br />means of determining areal sources of pollution). I refer to the above set of <br />measurement-related techniques and methods as "salinity assessment". Theory, <br />equipment and practical technology has been developed for this purpose. It is described <br />in a book to be published very soon'. I recommend that salinity assessment programs <br />based on this technology, which provide the kind of required information described <br />above in a timely and efficient way, should be implemented in Colorado. <br /> <br />Conclusions <br /> <br />The seriousness of the increasing salinity problems in Colorado needs to be fully grasped <br />by the responsible leaders and agricultural and water resource managers in the state and <br />appropriate policies and effective programs need to be developed and implemented to <br />deal with this most serious matter. The effectiveness of irrigation needs to be enhanced, <br />the return of drainage waters to fresh-water supplies needs to be curtailed and drainage <br />waters need to be isolated and reused for irrigation to help meet the future water- <br />supply/food production needs and to reduce the degradation of Colorado's soil and water <br /> <br />4 Rhoades, J. D., et aI., 1997. Assessing irrigation/drainage/salinity management using spatially referenced <br />salinity measurements. Agr. WaterMgt. 35:147-165. <br />, Rhoades, 1. D., etal., 1999. Soil Salinity Assessment: Methods of Electrical Conductivity Measurement <br />and Interpretation, Food and Agriculture Organization of the United Nations, Rome, Italy. <br />