88
5. Calculation of production without investing the saved water in adding new
area: Under application of deficit irrigation, we assumed that the saved water
will be assigned to increase the cultivated area of another winter crop.
Water productivity values for each crop were calculated under the five studied
production alternatives. 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). In our assessment, we used crop water productivity to
compare between the five studied production alternatives because both production
amount and the applied irrigation water to produce this amount are included.
5.2 Onion Production and Deficit Irrigation
Onion plants have slow growth rate, shallow roots system and its above ground
biomass is small. Drinkwater and Janes (1955) reported that because onion plants
are a shallow-rooted, most of the roots were found in the top 0.18 m of soil and only
a few roots were found deeper than 0.31 m, thus the maximum root penetration was
found at 0.76 m. This trait limits the amount of soil water available to onion plants,
especially when grown on coarse-textured soils. Therefore, sprinkler and drip irrigation systems are well suited for this crop (Al-Jamal et al. 2001).
5.2.1 Effect of Water Stress on Onion
Onion plants were found to be sensitive to water deficit during the whole growing
season, rather than specific growth stage (Kadayifci et al. 2005). Patel and Rajput
(2013) indicated that it is better to maintain moderate stress during the whole growing season, rather than creating a stress during non-critical growth stages. Pelter
et al. (2004) indicated that the total onion yield was reduced as a result of imposed
soil water stress at any growth stage, but the greatest effect was found at the 5-leaf
and, 7-leaf stages, which reduced yield by 26% compared with the non-water stress
control. Furthermore, the reproductive stage is the most critical stage for water
stress because it strongly affect final yield (Patel and Rajput 2013).
5.2.2 Effect of Deficit Irrigation on Onion
Nagaz et al. (2012) reported that applying 60% of crop evapotranspiration caused
significant decreases in fresh yield, dry matter, bulbs per hectare, and bulb weight of
onion, compared to those under both full irrigation (100% ETc) and regulated deficit irrigation (80% ETc). Taha et al. (2019) indicated that saving 20% of the applied
S. Ouda et al.
5. Calculation of production without investing the saved water in adding new
area: Under application of deficit irrigation, we assumed that the saved water
will be assigned to increase the cultivated area of another winter crop.
Water productivity values for each crop were calculated under the five studied
production alternatives. 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). In our assessment, we used crop water productivity to
compare between the five studied production alternatives because both production
amount and the applied irrigation water to produce this amount are included.
5.2 Onion Production and Deficit Irrigation
Onion plants have slow growth rate, shallow roots system and its above ground
biomass is small. Drinkwater and Janes (1955) reported that because onion plants
are a shallow-rooted, most of the roots were found in the top 0.18 m of soil and only
a few roots were found deeper than 0.31 m, thus the maximum root penetration was
found at 0.76 m. This trait limits the amount of soil water available to onion plants,
especially when grown on coarse-textured soils. Therefore, sprinkler and drip irrigation systems are well suited for this crop (Al-Jamal et al. 2001).
5.2.1 Effect of Water Stress on Onion
Onion plants were found to be sensitive to water deficit during the whole growing
season, rather than specific growth stage (Kadayifci et al. 2005). Patel and Rajput
(2013) indicated that it is better to maintain moderate stress during the whole growing season, rather than creating a stress during non-critical growth stages. Pelter
et al. (2004) indicated that the total onion yield was reduced as a result of imposed
soil water stress at any growth stage, but the greatest effect was found at the 5-leaf
and, 7-leaf stages, which reduced yield by 26% compared with the non-water stress
control. Furthermore, the reproductive stage is the most critical stage for water
stress because it strongly affect final yield (Patel and Rajput 2013).
5.2.2 Effect of Deficit Irrigation on Onion
Nagaz et al. (2012) reported that applying 60% of crop evapotranspiration caused
significant decreases in fresh yield, dry matter, bulbs per hectare, and bulb weight of
onion, compared to those under both full irrigation (100% ETc) and regulated deficit irrigation (80% ETc). Taha et al. (2019) indicated that saving 20% of the applied
S. Ouda et al.