RELATIONSHIP BETWEEN SALINITY AND EFFICIENT WATER-USE

The relationship between salinity and water use efficiency is highly d ependent upon which definition of water use efficiency is used. The tw o 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 effi ciency. An array of models is available to simulate the effects of var ious irrigation management strategies with saline waters. Based on res ults computed from these models, which consider the osmotic and matric potential effects on plant growth, strategies can be developed to eff ectively use saline waters in crop production. The cyclic strategy of using waters of different salinities can effectively be used in mainta ining crop rotations which include both salt-sensitive and salt-tolera nt crops. The major deficiency of the models is that they do not accou nt for the effects of water quality on soil physical conditions with c onsequent effects on crop production. Indeed, the most limiting factor in use of saline waters on soils may be deterioration of soil physica l conditions. The deterioration of soil physical conditions does not r esult from using the high-salinity waters per se but from subsequent r ainfall or low salinity waters. Thus far the emphasis on using saline waters on crop production has centered on yields and less attention ha s been given to the long-term consequences on soil physical conditions . This factor requires further research and should be a focus of atten tion in future experiments. Relatively high saline water tables can be maintained without drainage if a non-saline source of water is availa ble, and irrigation amounts can be controlled. This strategy might inv oke the necessity for shifting irrigation systems from surface to pres surized systems. Eventually, some salt must be removed from the system . It is probably more efficient to allow it to become very concentrate d and remove small volumes to be disposed of in some manner rather tha n apply it to productive land.