19
Water productivity is a quantitative term used to define the relationship between
crop produced and the amount of water involved in crop production (Igbadun et al.
2006). Valipour (2014) defined water productivity as the ratio of yield or marketable
product to net income, or to water used by the crop. Optimization of irrigation strategy is necessary to increase water productivity and minimize yearly fluctuations of
crop production. Under limited water supplies, the farmer’s goal should be to maximize net income per unit water used rather than per unit land (Fereres and Soriano
2007). Water productivity increases under deficit irrigation, relative to its value
under full irrigation, as shown experimentally for many crops (Fan et al. 2005).
2.5 Strategies of Deficit Irrigation
2.5.1 Sustained Deficit Irrigation
Fernandes-Silva et al. (2018) defined sustained deficit irrigation as “an irrigation
strategy based on the distribution of a reduced water volume, controlled by a water
stress indicator or as a percentage of the full water requirements for a crop throughout the whole irrigation season, so that the water deficit is intended to be uniform
over the whole crop cycle to avoid the occurrence of severe water stress at any particular moment that might have unfortunate results”. Whereas, Sofo et al. (2012)
indicated that sustained deficit irrigation distributes a reduced water volume, as percentage of crop evapotranspiration, throughout the whole irrigation season. Many
studies assessed the effects of application of sustained deficit irrigation to crops.
Noreldin et al. (2015) tested the effect of reducing the applied irrigation water to
wheat by 25 and 20% under drip and sprinkler systems, respectively and they found
that wheat yield was reduced by 20 and 18%, respectively. Furthermore, Abdelraouf
et al. (2013) indicated that application of 75% of wheat water requirements under
sprinkler irrigation in sandy soil resulted in only 3% reduction in wheat yield as a
result of applying 100% of NPK via fertigation pump, which reduced the leaching
of fertilizer, improved plants growth and reduce yield losses under deduction of
25% of the applied irrigation water. In the same token, Taha and Ouda (2016) indicated that application of deficit irrigation to wheat, where 11% saving in the applied
water under sprinkler system and fertigation in 80% of irrigation time resulted in
2% yield losses. Whereas, fertigation in 60% of irrigation time resulted in saving the
same amount of irrigation water with higher yield losses, namely 8%. Other studies
compared irrigation regimes based on different levels of crop evapotranspiration
restitution and their influence on fruit and oil quality of different olive cultivars.
Berenguer et al. (2006) found that a restitution ranging from 66% to 75% of crop
evapotranspiration is enough to obtain good yields similar to those harvested from
fully irrigated olive trees. However, Dabbou et al. (2010) indicated that phenolic
compounds in oils significantly decreased under the highest irrigation levels.
2 Deficit Irrigation and Water Conservation
Water productivity is a quantitative term used to define the relationship between
crop produced and the amount of water involved in crop production (Igbadun et al.
2006). Valipour (2014) defined water productivity as the ratio of yield or marketable
product to net income, or to water used by the crop. Optimization of irrigation strategy is necessary to increase water productivity and minimize yearly fluctuations of
crop production. Under limited water supplies, the farmer’s goal should be to maximize net income per unit water used rather than per unit land (Fereres and Soriano
2007). Water productivity increases under deficit irrigation, relative to its value
under full irrigation, as shown experimentally for many crops (Fan et al. 2005).
2.5 Strategies of Deficit Irrigation
2.5.1 Sustained Deficit Irrigation
Fernandes-Silva et al. (2018) defined sustained deficit irrigation as “an irrigation
strategy based on the distribution of a reduced water volume, controlled by a water
stress indicator or as a percentage of the full water requirements for a crop throughout the whole irrigation season, so that the water deficit is intended to be uniform
over the whole crop cycle to avoid the occurrence of severe water stress at any particular moment that might have unfortunate results”. Whereas, Sofo et al. (2012)
indicated that sustained deficit irrigation distributes a reduced water volume, as percentage of crop evapotranspiration, throughout the whole irrigation season. Many
studies assessed the effects of application of sustained deficit irrigation to crops.
Noreldin et al. (2015) tested the effect of reducing the applied irrigation water to
wheat by 25 and 20% under drip and sprinkler systems, respectively and they found
that wheat yield was reduced by 20 and 18%, respectively. Furthermore, Abdelraouf
et al. (2013) indicated that application of 75% of wheat water requirements under
sprinkler irrigation in sandy soil resulted in only 3% reduction in wheat yield as a
result of applying 100% of NPK via fertigation pump, which reduced the leaching
of fertilizer, improved plants growth and reduce yield losses under deduction of
25% of the applied irrigation water. In the same token, Taha and Ouda (2016) indicated that application of deficit irrigation to wheat, where 11% saving in the applied
water under sprinkler system and fertigation in 80% of irrigation time resulted in
2% yield losses. Whereas, fertigation in 60% of irrigation time resulted in saving the
same amount of irrigation water with higher yield losses, namely 8%. Other studies
compared irrigation regimes based on different levels of crop evapotranspiration
restitution and their influence on fruit and oil quality of different olive cultivars.
Berenguer et al. (2006) found that a restitution ranging from 66% to 75% of crop
evapotranspiration is enough to obtain good yields similar to those harvested from
fully irrigated olive trees. However, Dabbou et al. (2010) indicated that phenolic
compounds in oils significantly decreased under the highest irrigation levels.
2 Deficit Irrigation and Water Conservation