33
crop water requirement depends on them, namely reference evapotranspiration and
seasonal crop coefficients.
3.2.2.1 Reference evapotranspiration
Reference evapotranspiration (ETo) is the total amount of water lost from the field
by both soil evaporation and plant transpiration (Gardner et al. 1985). It is a key
component in irrigation scheduling for crops and water requirement calculation.
Various equations have been developed to estimate ETo. The Penman-Monteith
equation (Allen et al. 1998) is widely recommended because of its detailed
theoretical base and its accommodation of small time periods. It was also indicated
that the Penman-Monteith method exhibited excellent performance in both arid and
humid climates (Shahidian et al. 2012).
Ouda and Noreldin (2017) indicated that there is evidences of an increasing trend
in ETo values calculated from 30-year interval (1986–2015) illustrated by higher
mean values of ETo in the 10-year interval (2006–2015), compared to the mean
value of 20-year time interval (1996–2015) (Fig. 3.2).
3.2.2.2 Seasonal Crop Coefficients
Seasonal crop coefficients (Kc) takes into account the relationship between atmosphere, crop physiology, and agricultural practices (Snyder et al. 2004). Multiplication
of ETo by Kc values results in the value of crop evapotranspiration (ETc, or water
consumptive use by the crop). Table 3.3 presents the values of Kc (initial, middle
and end season) and ETc value of different crops cultivated in the winter season. The
table indicated that spring sugarcane has the highest ETc values as a result of its long
Table 3.2 Planting and harvest dates for the selected summer field and vegetable crops
Crop
Planting date
Harvest date
Season length (days)
Cotton
15-Mar
15-Aug
154
Maize
15-May
1-Sep
110
Rice
15-May
16-Sep
125
Sorghum
15-May
1-Sep
110
Soybean
15-May
25-Aug
103
Sunflower
15-May
15-Aug
93
Wheat
15-Nov
18-Apr
155
Spring sugarcane
15-Feb
14-Feb
365
Cucumber
15-Mar
15-Jun
93
Eggplant
1-Apr
1-Aug
130
Pepper
1-Apr
8-Aug
130
Potato
1-Aug
28-Nov
120
Tomato
1-May
1-Sep
124
Source: Ouda (2019)
3 Egypt Faces Water Deficiency, and Food Insufficiency
crop water requirement depends on them, namely reference evapotranspiration and
seasonal crop coefficients.
3.2.2.1 Reference evapotranspiration
Reference evapotranspiration (ETo) is the total amount of water lost from the field
by both soil evaporation and plant transpiration (Gardner et al. 1985). It is a key
component in irrigation scheduling for crops and water requirement calculation.
Various equations have been developed to estimate ETo. The Penman-Monteith
equation (Allen et al. 1998) is widely recommended because of its detailed
theoretical base and its accommodation of small time periods. It was also indicated
that the Penman-Monteith method exhibited excellent performance in both arid and
humid climates (Shahidian et al. 2012).
Ouda and Noreldin (2017) indicated that there is evidences of an increasing trend
in ETo values calculated from 30-year interval (1986–2015) illustrated by higher
mean values of ETo in the 10-year interval (2006–2015), compared to the mean
value of 20-year time interval (1996–2015) (Fig. 3.2).
3.2.2.2 Seasonal Crop Coefficients
Seasonal crop coefficients (Kc) takes into account the relationship between atmosphere, crop physiology, and agricultural practices (Snyder et al. 2004). Multiplication
of ETo by Kc values results in the value of crop evapotranspiration (ETc, or water
consumptive use by the crop). Table 3.3 presents the values of Kc (initial, middle
and end season) and ETc value of different crops cultivated in the winter season. The
table indicated that spring sugarcane has the highest ETc values as a result of its long
Table 3.2 Planting and harvest dates for the selected summer field and vegetable crops
Crop
Planting date
Harvest date
Season length (days)
Cotton
15-Mar
15-Aug
154
Maize
15-May
1-Sep
110
Rice
15-May
16-Sep
125
Sorghum
15-May
1-Sep
110
Soybean
15-May
25-Aug
103
Sunflower
15-May
15-Aug
93
Wheat
15-Nov
18-Apr
155
Spring sugarcane
15-Feb
14-Feb
365
Cucumber
15-Mar
15-Jun
93
Eggplant
1-Apr
1-Aug
130
Pepper
1-Apr
8-Aug
130
Potato
1-Aug
28-Nov
120
Tomato
1-May
1-Sep
124
Source: Ouda (2019)
3 Egypt Faces Water Deficiency, and Food Insufficiency