As a result of improved irrigation management and systems, growers in the Lower Murray (Riverland-Sunraysia) horticultural region have improved their water use efficiency (WUE) over the past two decades from about 50% to about 80%. However a negative consequence of this achievement is the emerging risk of salinity build-up in the root zone, threatening the sustainability of the region (Biswas et al. 2005a; Biswas et al. 2005b). The amount of irrigation applied must account for