When land becomes salinized it is abandoned. Over the last decade, efforts have been made to reclaim salinized land for some sort of economic return. Halophytic plants have been investigated for this purpose. Halophytes are the native flora of saline soils, and can complete their life cycle at salinities above 250 mM NaCl. Most halophytes need at least 1 mM NaCl to grow well, many need 10-50 mM NaCl to reach maximum growth, and a few grow best at 200-300 mM NaCl (Flowers et al., 1986). Many halophytes are very slow-growing even at their optimal salinity, but a few are suitable for reclamation. For instance, tall wheat grass (Thinopyrum ponticum, a decaploid form of Agropyrum elongatum) is widespread in many continents and now planted as a fodder species in saline soil. Another species being planted for fodder is the dicotyledenous halophyte, Atriplex amnicola, a saltbush species native to Western Australia. Some halophytes are more tolerant than this, but A. amnicola shows the growth maximum at low salinity and the extended growth at very high salinities that is typical of many dicotyledenous halophytes.
Recently there has been strong interest in the salinity tolerance of trees that are not halophytes but have good salinity tolerance and high transpiration rates that can be planted in saline soils to lower water tables. Such species need also to be tolerant of waterlogging as secondary salinity occurs with rising water tables, so the ability to withstand periods of waterlogging and to continue high transpiration rates is essential. In Australia, river red gum (Eucalptus camaldulensis) has been the most widely used. However there are a number of other species that are better able to tolerate saline and waterlogged soils. Many Acacia, Casuarina and Melaleuca species are tolerant of high salinity; for example A. stenophylla did not suffer a 50% growth reduction until an ECe of 20 dS m-1, equivalent to about 200 mM NaCl (Marcar et al., 1995). Such species are recommended for reclamation of land that has become saline because of irrigation, as they provide some income to farmers as fodder and fuelwood.
