17
dioxide supply as a result of stomata closure reduces assimilative capacity due to
decreasing photosynthesis, thus, translocation of carbohydrates and plant-growth
regulators decrease, which disturb nitrogen metabolism (Kramer 1983) and reduces
final crop yield (Taiz and Zeiger 2004).
Production of abscisic acid in leaves increases under water stress by about 50-fold,
which cause stomatal closure and the induction of senescence and ethylene production (Taiz and Zeiger 2013). Water stress also affects many important biochemical
processes such as osmotic adjustment, antioxidant enzyme defense system, and lipid
peroxidation (Sarto et al. 2017). However, plants protects themselves from drought
by morphological, physiological, and biochemical processes (Sarto et al. 2016).
These processes are influenced by the level of CO 2 , solar radiation, temperature, and
relative humidity (Grant 1992). The increase in Si in the plant can increase the efficiency of water use by some grasses (Sarto et al. 2016). Under severe stress, the
dehydration in mesophyll cells inhibits photosynthesis, as well as mesophyll metabolism, and water-use efficiency decreases as a result (Taiz and Zeiger 2004).
2.3 Deficit Irrigation Concept and Definitions
English and Nuss (1982) developed the concept of deficit irrigation and define it as
“the practice of deliberately under-irrigating a crop, where its irrigation water supply is reduced relative to that needed to meet its maximum evapotranspiration”. The
concept of deficit irrigation was further developed by English (1990) as “the deliberate and systematic under-irrigation of crops during the entire biological cycle with
acceptance of a certain yield reduction”. His definition also included an analytical
framework to estimate the profit-maximizing level of water use. Fereres and Soriano
(2007) stated that deficit irrigation should be defined in terms of the level of water
supply in relation to maximum crop evapotranspiration and a maximum yield is not
sought. Another terminology for deficit irrigation was developed by Capra et al.
(2008) as the application of irrigation below the full crop evapotranspiration, which
potentially improve efficiency and maximize profits through a reduction in capital
and operating costs. Whereas, Chai et al. (2016) stated that deficit irrigation is considered as an irrigation practice characterized by application of irrigation water
below the full required amounts for optimal growth and yield, aiming at improving
the response of plants to the certain degree of water deficit in a positive manner, and
improving crop’s water use efficiency. Thus, deficit irrigation is looked upon as a
key contributor in water saving technology.
Capra et al. (2008) reported that a number of authors, who have adopted the
“English definition of deficit irrigation”, dealt only with the physiological and agronomical aspects of deficit irrigation, namely crop response to different irrigation
regimes without any economic evaluation, which created some misunderstanding.
2 Deficit Irrigation and Water Conservation
dioxide supply as a result of stomata closure reduces assimilative capacity due to
decreasing photosynthesis, thus, translocation of carbohydrates and plant-growth
regulators decrease, which disturb nitrogen metabolism (Kramer 1983) and reduces
final crop yield (Taiz and Zeiger 2004).
Production of abscisic acid in leaves increases under water stress by about 50-fold,
which cause stomatal closure and the induction of senescence and ethylene production (Taiz and Zeiger 2013). Water stress also affects many important biochemical
processes such as osmotic adjustment, antioxidant enzyme defense system, and lipid
peroxidation (Sarto et al. 2017). However, plants protects themselves from drought
by morphological, physiological, and biochemical processes (Sarto et al. 2016).
These processes are influenced by the level of CO 2 , solar radiation, temperature, and
relative humidity (Grant 1992). The increase in Si in the plant can increase the efficiency of water use by some grasses (Sarto et al. 2016). Under severe stress, the
dehydration in mesophyll cells inhibits photosynthesis, as well as mesophyll metabolism, and water-use efficiency decreases as a result (Taiz and Zeiger 2004).
2.3 Deficit Irrigation Concept and Definitions
English and Nuss (1982) developed the concept of deficit irrigation and define it as
“the practice of deliberately under-irrigating a crop, where its irrigation water supply is reduced relative to that needed to meet its maximum evapotranspiration”. The
concept of deficit irrigation was further developed by English (1990) as “the deliberate and systematic under-irrigation of crops during the entire biological cycle with
acceptance of a certain yield reduction”. His definition also included an analytical
framework to estimate the profit-maximizing level of water use. Fereres and Soriano
(2007) stated that deficit irrigation should be defined in terms of the level of water
supply in relation to maximum crop evapotranspiration and a maximum yield is not
sought. Another terminology for deficit irrigation was developed by Capra et al.
(2008) as the application of irrigation below the full crop evapotranspiration, which
potentially improve efficiency and maximize profits through a reduction in capital
and operating costs. Whereas, Chai et al. (2016) stated that deficit irrigation is considered as an irrigation practice characterized by application of irrigation water
below the full required amounts for optimal growth and yield, aiming at improving
the response of plants to the certain degree of water deficit in a positive manner, and
improving crop’s water use efficiency. Thus, deficit irrigation is looked upon as a
key contributor in water saving technology.
Capra et al. (2008) reported that a number of authors, who have adopted the
“English definition of deficit irrigation”, dealt only with the physiological and agronomical aspects of deficit irrigation, namely crop response to different irrigation
regimes without any economic evaluation, which created some misunderstanding.
2 Deficit Irrigation and Water Conservation