ALTERNATE PARTIAL ROOT-ZONE SURFACE DRIP IRRIGATION FOR TOMATO: HYDRUS-2D - Management, Performance, and Applications of Micro Irrigation Systems - page 122

2

( )

()

⎡

m

⎤

l 1 m

Kh = KS 11 − − S

⎢ ⎥

se

⎣

e

⎦

(3)

where: θ (h) is the soil water retention (L 3 L -3 ), θ s is the saturated water content (L 3 L -3 ),
θ r is the residual water content (L 3 L -3 ), α is related to the inverse of a characteristic
pore radius (L -1 ), l is shape parameter, n is a pore-size distribution index, m = 1-1/n,
and Se is the effective saturation given by:

θ−θ
= θ−θ S

r

e

(4)

s r

9.2.6 SOLUTE PARAMETERS
Longitudinal dispersivity (ε L ) was approximated to one-tenth of the profile depth [2,
4]. The transversal dispersivity ε T was set to = 0.1(ε L ). Adsorption isotherm and mo-
lecular diffusion were ignored during simulation. Salinity transport was simulated
based on the hypothesis that the solutes were nonreactive and there was neither net
solubilization nor dissolution.

9.2.7 ROOT WATER UPTAKE PARAMETERS
Root water uptake has a crucial effect on the spatial distribution of water and soil
water salinity in the flow domain. Feddes et al. [6] presented a threshold water stress
response function that describes the water uptake from the soil. The following param-
eters by Feddes et al. [6], model were used in simulation: P o = −1, P opt = −2, P 2high =
−800, P2 low = −1500, P 3 = −8000 cm, r 2high = 0.5 cm.d -1 , r 2low = 0.1 cm d -1 . The osmotic
effects were included using threshold model [19] with threshold = 2.5 dS.m -1 and a
slope of 9.9%. The Vrugt model [24] was used to illustrate the root distribution for
tomato. The root distribution for tomato crop was set as reported by Hanson et al. [8].
It is worthwhile to observe that the assumed root distribution was used for all simula-
tion scenarios because of the lack of information for root distribution under certain
scenarios.

FIGURE 2 Root distribution (percentages of the total roots) used for HYDRUS-2D simulation.

9.2.8 SIMULATION SCENARIOS
Series of simulations were performed including two varying factors; salinity of irriga-
tion water and the interemitter plant distance. Simulations were conducted for loamy