ALTERNATE PARTIAL ROOT-ZONE SURFACE DRIP IRRIGATION FOR TOMATO: HYDRUS-2D - Management, Performance, and Applications of Micro Irrigation Systems - page 121

9.2.3 BOUNDARY CONDITIONS
No flux was allowed through the vertical sides of the soil domain due to symmetry. A
free drainage boundary was set at the bottom boundary because the water table is situ-
ated far below the domain of interest (about 1.50 m below the soil surface). Variable
flux boundary condition was assumed at the top boundary in the location of trickle
emitter during irrigation time and no flux in fallow time. The remaining part of the top
boundary was assigned atmospheric boundary condition allowing for crop evapotrans-
piration (ETc). Crop ETc was calculated with the Penman-Monteith equation for a
reference crop (ETo) values obtained from the weather conditions and crop coefficient
(Kc) value. ETc was computed from the product of ETo and the crop coefficient (for
tomato, Kc = 1.05 from FAO, 5). During simulation, potential evapotranspiration was
partitioned into potential evaporation (Ep = 0.05ETc) and potential transpiration (Tp
= 0.95ETc).
Bonchela et al. [3] concluded that evaporation from emitter zone in olive orchards
with 36% ground cover ranged from 4 to 12%. The effect of saline irrigation water was
simulated by assuming a third-type boundary condition at the emitter location and the
solute was accompanied with the irrigation water. In this study, the salinity of irriga-
tion water was taken equal to 0, 1.00, and 2.00 dS/m (the salinity of El-Salam Canal
water ranges from 1.00 to 2.00 dS/m).

9.2.4 INITIAL CONDITIONS
Uniform initial water content of 0.199 m 3 m -3 was set throughout the flow domain and
initial solute concentration was set equal to 2.00 dS/m. Soil salinity measurements
in El-Salam Canal cultivated land (study area) in previous field experiments were
conducted by Abou Lila et al. [1] and they found the soil salinity range of 0.70 to 3.50
dS/m.

TABLE 1 Hydraulic parameters of simulated soil.

Soil Type θ r θ s α n ks (cm/day) L

Loamy sand 0.074 0.453 0.045 1.72 288.5 0.5

9.2.5. SOIL PROPERTIES
Soil hydraulic properties used for model execution (Table 1) were estimated using
standard laboratory methods (Pressure plate extractor set) for soil samples collected
from El-Salam Canal cultivated land. The soil hydraulic properties in HYDRUS-2D
are based on the van Genuchten-Mualem model [23]:

(2)