Salinity and Avocado Production, A Review

Salinity refers to the occurrence of high concentrations of dissolved major inorganic ions in solution; including Na +, Mg 2+ , Ca 2+ , K + , HCO 3-, SO4 2-and Cl - (Mwai, 2001).The most common ions in the soil and at high concentrations are Na + and Cl - (Soussi et al., 1998).Saline soils are characterized by having an electrical conductivity higher than 4 dS m1 (where 4 dS m1 40 mM NaCl), which many crops are unable to tolerate (Qadir et al., 2000).It is formed under hot, arid conditions due to an accumulation of salts in the topsoil and form naturally or as a result of poorly managed irrigation (Mwai, 2001).Saline soils also occur where the supply of salts, for example from rock weathering capillary rise, rainfall or flooding, exceeds their removal; for example by leaching or flooding (Landon, 1991).Salinity is one of the most significant environmental challenges limiting plant productivity, particularly in arid and semi-arid climates.It is one of the major abiotic constraints on agriculture worldwide, and the situation has worsened over the last 20 years due to the increase in irrigation requirements in arid and semi-arid regions.Salinization due to injudicious irrigation is recognized as being responsible for the loss of large tracts of agricultural land for cultivation (Mwai, 2001).Soil salinity affects about 7% of the world's total land area (Musyimi, 2005) and 800 million hectares of arable lands worldwide (Munns and Tester, 2008).Salinity/Salt stress is a global problem that limits crop production.It is also one of the major factors reducing plant growth and productivity (Musyimi, 2005).It also cause decreases in photosynthesis (Netondo et al., 2004a).Three major hazards associated with salinity are: -osmotic stress, ion toxicity and mineral deficiencies (Hasegawa et al., 2000; Netondo et al., 2004a).Soil salinity not only delays but also reduces flowering and yield of crop plants.Avocado is known to be the most salt-sensitive cultivated fruit tree.Even low levels of salt inhibit the vegetative growth of the avocado shoot (Bernstein et al., 2001;Mickelbart and Arpaia, 2002).