Water is a precious natural resource for mankind. Shortage of freshwater resources is one of the main environmental problems in many regions of the world, and its importance will increase in the near future because of the growing pressure on water resources and the effects of climate change (Shannon et al., 2008; Lado and Ben-Hur, 2009). Agriculture worldwide is heavily dependent on water availability, making water management one of the most important components of modern agriculture. Water is the solvent and transport medium in natural systems. In general, the cultivation of plants is impossible without water. For normal growth and maturation of plants, the availability and preservation of suf‰cient soil moisture during the whole plant maturation period is required (Hamzei, 2011). Water is a major constituent of plants and microbes and a reactant or substrate in many important processes crucial for metabolic activity (Hinsinger et al., 2009). Another role of water is the maintenance of turgor, which is essential for cell enlargement and growth (Kramer and Boyer, 1995). The absorption of water in adequate amount by roots is the main factor for the optimal growth and development of plants.