The Salinity Problem in General, Its Importance, and Distribution with Special Reference to Natural Halophytes

Abstract

A salinity problem is regarded as arising when the concentration of sodium chloride, sodium carbonate, sodium sulphate or salts of magnesium are present in excess, and when the effect becomes increasingly evident the greater the excess. There has, however, been considerable debate over the exact point, in respect of salt concentration, where the salinity problem first appears, i.e. the point where one passes from glycophytic to halophytic conditions and vice versa. At present only sodium chloride of the above alkali salts has really been studied sufficiently, and there is no evidence to suggest any departure from the earlier figure of 0.5% in the soil solution (Chapman, 1966; Chapman, 1974). It is true that there are some economic plants that can be grown satisfactorily using irrigation water containing 1% NaCl provided the substrate has a high permeability, e.g. sand (Boyko, 1966). It is also evident that the effect of increased salinity upon plants is determined not only by the absolute quantity of the ions in excess, but also by the relative amounts of certain other ions, especially SO ⁼₄ (Strogonov, 1964). Some excess is not necessarily deleterious, because Boyko (1966) has suggested that with certain plants, temporary or permanent salinization may give increased resistance to drought and disease, and this led him to propound his concept of “raised vitality”.