20
2.5.2 Regulated Deficit Irrigation
Regulated deficit irrigation was proposed in the first time by Chalmers et al. (1981).
This irrigation strategy reduces water supplies during specific periods characterized
by a less plant sensibility to water stress with minimal effects on yield. Research on
regulated deficit irrigation could also be viewed as research on the crop coefficient
in different phenological phases (Capra et al. 2008). Regulated deficit irrigation has
been adapted successfully for some tree crops (Girona et al. 2005). It has been also
applied to sugar beet (Fabeiro et al. 2003), tomato (Hsiao 1993) and cotton (Snyder
1992). In this strategy, vegetative and reproductive growth are controlled by water
stress through water deficits imposed during crop growing phases that are not yield
reducing (Girona et al. 2005). Du et al. (2014) reported that there is some potential
to practice regulated deficit irrigation on cereal crops in the arid north and northwest of China, where it was shown that regulated deficit irrigation can maintain a
similar yield level under mild water stress during earlier stages and it significantly
enhanced water used efficiency. Other studies on the effect of regulated deficit irrigation indicated that this practice increases root to shoot ratio (Vandoorne et al. 2012).
Chai et al. (2016) identified three main regulated deficit irrigation approaches in
the production of agricultural crops, namely stage-based deficit irrigation, partial
root-zone irrigation and subsurface irrigation or infiltration movement as followed.
2.5.2.1 Stage-Based Deficit Irrigation
The principle behind this approach is that the response of plants to regulated deficit
irrigation varies with growth stages, where less applied water at non-critical stages
cause no yield losses (Hongbo et al. 2005). Assuming that critical growth stages are
determined, this approach could cause insignificant negative impact on plant productivity even though it may reduce normal plant growth (Chai et al. 2016). The
sensitivity of any plant growth stage to water deficit is affected by many factors,
including climatic conditions, crop species and cultivars, where cultivars differ in
photosynthetic rate, stomatal conductance, and transpiration rate, thus they express
different degrees of responses to water stress (Hongbo et al. 2005). Timing and the
extent to which stage-based deficit irrigation is applied plays a critical role in plant
recovery from deficit-induced stress (Chai et al. 2016). Stage-based deficit irrigation could help in improving the adaptability of plants to the stress through a stressinduced acclimatization process.
In wheat, the most sensitive growth stage to lack of water is the flag leaf stage,
followed by the flowering stage (Kirigwi et al. 2004). Rodrigues et al. (1998)
highlighted three critical periods wherein the occurrence of drought most affects the
wheat crop: floral initiation and inflorescence development, anthesis and fertilization, and grain formation. Dias (2008) indicated that the greatest reduction in wheat
grains yield occur when plants suffer from water deficiency during 15 days before
and 5 days after heading. On the other hand, in maize, drought occurring between
S. Ouda and T. Noreldin
2.5.2 Regulated Deficit Irrigation
Regulated deficit irrigation was proposed in the first time by Chalmers et al. (1981).
This irrigation strategy reduces water supplies during specific periods characterized
by a less plant sensibility to water stress with minimal effects on yield. Research on
regulated deficit irrigation could also be viewed as research on the crop coefficient
in different phenological phases (Capra et al. 2008). Regulated deficit irrigation has
been adapted successfully for some tree crops (Girona et al. 2005). It has been also
applied to sugar beet (Fabeiro et al. 2003), tomato (Hsiao 1993) and cotton (Snyder
1992). In this strategy, vegetative and reproductive growth are controlled by water
stress through water deficits imposed during crop growing phases that are not yield
reducing (Girona et al. 2005). Du et al. (2014) reported that there is some potential
to practice regulated deficit irrigation on cereal crops in the arid north and northwest of China, where it was shown that regulated deficit irrigation can maintain a
similar yield level under mild water stress during earlier stages and it significantly
enhanced water used efficiency. Other studies on the effect of regulated deficit irrigation indicated that this practice increases root to shoot ratio (Vandoorne et al. 2012).
Chai et al. (2016) identified three main regulated deficit irrigation approaches in
the production of agricultural crops, namely stage-based deficit irrigation, partial
root-zone irrigation and subsurface irrigation or infiltration movement as followed.
2.5.2.1 Stage-Based Deficit Irrigation
The principle behind this approach is that the response of plants to regulated deficit
irrigation varies with growth stages, where less applied water at non-critical stages
cause no yield losses (Hongbo et al. 2005). Assuming that critical growth stages are
determined, this approach could cause insignificant negative impact on plant productivity even though it may reduce normal plant growth (Chai et al. 2016). The
sensitivity of any plant growth stage to water deficit is affected by many factors,
including climatic conditions, crop species and cultivars, where cultivars differ in
photosynthetic rate, stomatal conductance, and transpiration rate, thus they express
different degrees of responses to water stress (Hongbo et al. 2005). Timing and the
extent to which stage-based deficit irrigation is applied plays a critical role in plant
recovery from deficit-induced stress (Chai et al. 2016). Stage-based deficit irrigation could help in improving the adaptability of plants to the stress through a stressinduced acclimatization process.
In wheat, the most sensitive growth stage to lack of water is the flag leaf stage,
followed by the flowering stage (Kirigwi et al. 2004). Rodrigues et al. (1998)
highlighted three critical periods wherein the occurrence of drought most affects the
wheat crop: floral initiation and inflorescence development, anthesis and fertilization, and grain formation. Dias (2008) indicated that the greatest reduction in wheat
grains yield occur when plants suffer from water deficiency during 15 days before
and 5 days after heading. On the other hand, in maize, drought occurring between
S. Ouda and T. Noreldin