Relationship between salinity and efficient water use

The relationship between salinity and water use efficiency is highly dependent upon which definition of water use efficiency is used. The two common definitions, yield per unit evapotranspiration and yield per unit applied water, both have significant deficiencies and can lead to erroneous conclusions. Thus, the analysis of efficient use of saline waters invokes a broader analysis than merely computing water use efficiency. An array of models is available to simulate the effects of various irrigation management strategies with saline waters. Based on results computed from these models, which consider the osmotic and matric potential effects on plant growth, strategies can be developed to effectively use saline waters in crop production. The cyclic strategy of using waters of different salinities can effectively be used in maintaining crop rotations which include both salt-sensitive and salt-tolerant crops. The major deficiency of the models is that they do not account for the effects of water quality on soil physical conditions with consequent effects on crop production. Indeed, the most limiting factor in use of saline waters on soils may be deterioration of soil physical conditions. The deterioration of soil physical conditions does not result from using the high-salinity waters per se but from subsequent rainfall or low salinity waters. Thus far the emphasis on using saline waters on crop production has centered on yields and less attention has been given to the long-term consequences on soil physical conditions. This factor requires further research and should be a focus of attention in future experiments. Relatively high saline water tables can be maintained without drainage if a non-saline source of water is available, and irrigation amounts can be controlled. This strategy might invoke the necessity for shifting irrigation systems from surface to pressurized systems. Eventually, some salt must be removed from the system. It is probably more efficient to allow it to become very concentrated and remove small volumes to be disposed of in some manner rather than apply it to productive land.