ABSTRACT
Due to population growth, the demand on water resources increases. One option for coping with this is to minimize the use of irrigation practices that are wasteful in their water consumption as well as using brackish water as alternative irrigation water resources especially in arid and semiarid areas. Egypt is considered one of the water scarce arid countries in the Middle East. Water scarcity is forcing Egypt to use brackish water as an alternative source for crop irrigation. The El-Salam Canal is one of the five mega irrigation projects in Egypt and used to irrigate 2.6 billion m2 of new reclaimed areas in the Eastern Delta and North Sinai. Canal water is a mixture of 1.9 billion m3/year of drainage water and 2.1 billion m3/year of fresh water from the river Nile. Recently in Egypt, modern irrigation techniques are being called on to produce more food with less irrigation water. Conventional deficit irrigation (CDI), considering crop tolerance to water stress during its growing stages, is one approach that can diminish water use without distinct yield reduction [15]. Alternate partial root irrigation (APRI) is another water-saving irrigation technique in which irrigation amount can be reduced without significant reduction in crop yield [16]. In this technique, approximately half of the root system is always exposed to drying soil while the remaining half is irrigated as in full irrigation. The wetted and dry sides of the root system are alternated with a frequency according to soil water balance and crop water requirement [13]. Zhang et al. [26] demonstrated that plants with two halves of their roots under alternating drying and wetting cycles developed normally with reduced stomatal opening and without considerable leaf water deficit. Laboratory studies conducted by many researchers [18, 26, 27, 28] manifested that stomatal regulation is managed through chemical signals from plant roots to leaves. These signals depended mainly on the development of abscisic acid (ABA) in plant roots in the drying soil. ABA transported through the transpiration streams and the augment of ABA concentration in plant xylem causes closure of stomata. Thereby, the luxury transpiration was reduced without any effect on photosynthesis [11, 22].
