21
2 weeks before and 2 weeks after the silking stage can cause significant reductions
in kernel set and kernel weight (Schussler and Westgate 1991). A short duration of
water deficit during tasselling stage in maize resulted in reduction in biomass production and grain yield by 30 and 40%, respectively (Çakir 2004). Kamara, et al.
(2003) reported that water deficit reduced biomass accumulation by 37% at silking,
by 34% at grain filling period, and by 21% at maturity. A comparison was made
between maize yield resulted from deficit irrigation applied during the vegetative
stage and deficit irrigation applied during the whole growing season revealed that
yield increase by 10–20% in the first case, compare to the second case (Domínguez
et al. 2012). Furthermore, maize plants that recovered from water stress during
seedling-stage were better adapted to soil water deficit occurring later in the life
cycle (Siddique and Bramley 2014). Kuşçu et al. (2014) indicated that application
of full irrigation until the beginning of the fruit ripening stage and the cessation of
irrigation thereafter in tomato resulted in 33% saving in irrigation water and 42%
increase in water use efficiency, in addition to 5% yield loss.
2.5.2.2 Partial Root-Zone Irrigation
Partial root-zone irrigation is a strategy of deficit irrigation that involves irrigating
only one half of the root zone in each irrigation event, while the other half is allowed
to dry, thus both halves are watered alternately (Dry and Loveys 1998). This strategy
is divided into two approaches. The first approach is watering and drying of root zone
are alternated in a pre-set frequency that allows the previously well-watered side of
the root zone to dry down while fully irrigating the previously dried root zones
according to water requirements of the crop species, growth stages, and soil water
holding capacity at the time of irrigation. The second approach is called fixed partial
root-zone irrigation, which depends on irrigation of half of the root system irrigated
in a normal amount each time when irrigation is applied, and the remaining half is
always exposed to drying soil (Chai et al. 2016). In both approaches, it is assumed
that respond of the fraction of the root system under drying soil was done by sending
a root-sourced signal to the shoot where stomata may close to reduce water loss
through transpiration (Liu et al. 2006). Furthermore, reduction in the applied amount
of water to plants cause a small narrowing of the stomatal opening, which helps
reduce water loss with little or no impact on plant photosynthesis (De Souza et al.
2005). The performance of partial-root drying strategy is based on the assumption
that photosynthesis and fruit growth are less sensitive to water deficit than transpiration, where the production of chemical signals is induced, namely ABA in the root
and translocated to leaves causing stomatal closure (Wilkinson and Hartung 2009).
Watering alternation between drying and wetting root zones with partial root-zone
irrigation allows roots to experience mild water stress first, and then, re-watering
provides a compensatory effect in enhancing root activity (Chai et al. 2016).
In a partial root-zone irrigation study for potato, water use was reduced by nearly
50% without reducing potato tuber yield, and water use efficiency was increased by
more than 50% (Xie et al. 2012). Furthermore, a partial root-zone irrigation study
2 Deficit Irrigation and Water Conservation
2 weeks before and 2 weeks after the silking stage can cause significant reductions
in kernel set and kernel weight (Schussler and Westgate 1991). A short duration of
water deficit during tasselling stage in maize resulted in reduction in biomass production and grain yield by 30 and 40%, respectively (Çakir 2004). Kamara, et al.
(2003) reported that water deficit reduced biomass accumulation by 37% at silking,
by 34% at grain filling period, and by 21% at maturity. A comparison was made
between maize yield resulted from deficit irrigation applied during the vegetative
stage and deficit irrigation applied during the whole growing season revealed that
yield increase by 10–20% in the first case, compare to the second case (Domínguez
et al. 2012). Furthermore, maize plants that recovered from water stress during
seedling-stage were better adapted to soil water deficit occurring later in the life
cycle (Siddique and Bramley 2014). Kuşçu et al. (2014) indicated that application
of full irrigation until the beginning of the fruit ripening stage and the cessation of
irrigation thereafter in tomato resulted in 33% saving in irrigation water and 42%
increase in water use efficiency, in addition to 5% yield loss.
2.5.2.2 Partial Root-Zone Irrigation
Partial root-zone irrigation is a strategy of deficit irrigation that involves irrigating
only one half of the root zone in each irrigation event, while the other half is allowed
to dry, thus both halves are watered alternately (Dry and Loveys 1998). This strategy
is divided into two approaches. The first approach is watering and drying of root zone
are alternated in a pre-set frequency that allows the previously well-watered side of
the root zone to dry down while fully irrigating the previously dried root zones
according to water requirements of the crop species, growth stages, and soil water
holding capacity at the time of irrigation. The second approach is called fixed partial
root-zone irrigation, which depends on irrigation of half of the root system irrigated
in a normal amount each time when irrigation is applied, and the remaining half is
always exposed to drying soil (Chai et al. 2016). In both approaches, it is assumed
that respond of the fraction of the root system under drying soil was done by sending
a root-sourced signal to the shoot where stomata may close to reduce water loss
through transpiration (Liu et al. 2006). Furthermore, reduction in the applied amount
of water to plants cause a small narrowing of the stomatal opening, which helps
reduce water loss with little or no impact on plant photosynthesis (De Souza et al.
2005). The performance of partial-root drying strategy is based on the assumption
that photosynthesis and fruit growth are less sensitive to water deficit than transpiration, where the production of chemical signals is induced, namely ABA in the root
and translocated to leaves causing stomatal closure (Wilkinson and Hartung 2009).
Watering alternation between drying and wetting root zones with partial root-zone
irrigation allows roots to experience mild water stress first, and then, re-watering
provides a compensatory effect in enhancing root activity (Chai et al. 2016).
In a partial root-zone irrigation study for potato, water use was reduced by nearly
50% without reducing potato tuber yield, and water use efficiency was increased by
more than 50% (Xie et al. 2012). Furthermore, a partial root-zone irrigation study
2 Deficit Irrigation and Water Conservation