16
land, where 70% of fresh water is withdrawn (FAO 2007). Coupled with the
projected climate change, the situation may get worst in the future (De Wit and
Stankiewicz 2006).
Irrigation is very important practice to attain high yield potential and increase
total production. Because irrigated agriculture is the largest fresh water user on the
planet (Gan et al. 2013), irrigation water has been over-exploited and over-used
(Chai et al. 2014). Additionally, irrigated agriculture is practice in many parts of the
world and water resources conservation and sustainability are not taking into consideration in many developing countries (Fereres and Soriano 2007). Some countries, like Egypt is recently transferred from the situation of water abundant to water
deficiency. Egypt has passed the threshold of water scarcity and reached the value
of 600 m
3
/capita/year (Ministry of Irrigation and Water Resources 2014). This value
is expected to reach 500 m
3
/capita/year in 2025, as a result of population increase.
Rapid urbanization in Egypt has caused conflict between the need for water for
agriculture and other sectors.
A strategic change in water resources management is taking place in many parts
of the world, where the supply available for irrigation is limited to what is left after
all other sectors satisfy their needs (Fereres and Soriano 2007). Under such situations, farmers often receive water allocations below the maximum evapotranspiration needs, and either have to concentrate the supply over a smaller land area or have
to irrigate the total area with level below full evapotranspiration (Vörösmarty et al.
2010a). Consequently, water resources available to agriculture will need to be rerationalized to satisfy the developmental needs of other sectors (Vörösmarty et al.
2010b). Deficit irrigation is one of the most important management strategies.
Fereres and Soriano (2007) defined deficit irrigation as an irrigation strategy to
maximize yield with a minimum rate of water application.
In this chapter, we tackled some of the concepts and definitions used in application of deficit irrigation instead of full irrigation as a technology aims at conserving
irrigation water.
2.2 Consequences of Water Stress on Plants
Water stress initiates a complex pathway, starting with the perception of stress,
which trigger a sequence of metabolic responses. Various levels of physiological
responses, both metabolic and developmental occur (Sarto et al. 2016). A reduction
in water availability in plants leads to the reduction of cell solutes, thus plasma
membrane become thicker, affecting the cells turgidity and causing stomatal closure
to prevent dehydration (Sarto et al. 2017). The turgor of the guard cells change to
control the opening and the closing of the stomata by hydropassive (without energy
expenditure) and hydroactive (with energy expenditure) movements resulted in
drastic reduction in transpiration rates (Taiz and Zeiger 2004). Reduction of carbon
S. Ouda and T. Noreldin
land, where 70% of fresh water is withdrawn (FAO 2007). Coupled with the
projected climate change, the situation may get worst in the future (De Wit and
Stankiewicz 2006).
Irrigation is very important practice to attain high yield potential and increase
total production. Because irrigated agriculture is the largest fresh water user on the
planet (Gan et al. 2013), irrigation water has been over-exploited and over-used
(Chai et al. 2014). Additionally, irrigated agriculture is practice in many parts of the
world and water resources conservation and sustainability are not taking into consideration in many developing countries (Fereres and Soriano 2007). Some countries, like Egypt is recently transferred from the situation of water abundant to water
deficiency. Egypt has passed the threshold of water scarcity and reached the value
of 600 m
3
/capita/year (Ministry of Irrigation and Water Resources 2014). This value
is expected to reach 500 m
3
/capita/year in 2025, as a result of population increase.
Rapid urbanization in Egypt has caused conflict between the need for water for
agriculture and other sectors.
A strategic change in water resources management is taking place in many parts
of the world, where the supply available for irrigation is limited to what is left after
all other sectors satisfy their needs (Fereres and Soriano 2007). Under such situations, farmers often receive water allocations below the maximum evapotranspiration needs, and either have to concentrate the supply over a smaller land area or have
to irrigate the total area with level below full evapotranspiration (Vörösmarty et al.
2010a). Consequently, water resources available to agriculture will need to be rerationalized to satisfy the developmental needs of other sectors (Vörösmarty et al.
2010b). Deficit irrigation is one of the most important management strategies.
Fereres and Soriano (2007) defined deficit irrigation as an irrigation strategy to
maximize yield with a minimum rate of water application.
In this chapter, we tackled some of the concepts and definitions used in application of deficit irrigation instead of full irrigation as a technology aims at conserving
irrigation water.
2.2 Consequences of Water Stress on Plants
Water stress initiates a complex pathway, starting with the perception of stress,
which trigger a sequence of metabolic responses. Various levels of physiological
responses, both metabolic and developmental occur (Sarto et al. 2016). A reduction
in water availability in plants leads to the reduction of cell solutes, thus plasma
membrane become thicker, affecting the cells turgidity and causing stomatal closure
to prevent dehydration (Sarto et al. 2017). The turgor of the guard cells change to
control the opening and the closing of the stomata by hydropassive (without energy
expenditure) and hydroactive (with energy expenditure) movements resulted in
drastic reduction in transpiration rates (Taiz and Zeiger 2004). Reduction of carbon
S. Ouda and T. Noreldin