These figures should only be used as a guide because the extent of salinity damage depends on the factors described above. If the salinity of the water to be used is near the upper recommended limit it is advisable to conduct preliminary trials under the specific soil, irrigation and climatic conditions present to determine if crop damage will occur. Changes of water salinity of 20 per cent above or below the indicated salt tolerance value may have little effect because of the modifying effect of soil, climate, and management. The yield loss data in Table 1 depends on several basic assumptions. These figures are applicable to surface irrigation and sprinkler irrigation methods which allow for an extended drying period between irrigations.
Crops can usually tolerate higher salinity of irrigation water under higher frequency irrigation.
These guidelines are likely to be too restrictive for sprinkler irrigation on the very permeable sands of the Swan Coastal Plain. Irrigation on these soils is frequent, often with a leaching fraction over 15 per cent. Sprinkler irrigation of crops with water high in chlorine or sodium may result in crop damage via foliar absorption even though the salinity concentration is below the critical level listed in Table 1 . The guidelines are too restrictive for drip irrigation. Drip irrigation is applied frequently which reduces salinity concentrations in the root zone and, in addition, increases in salinity due to evaporation are minimal.