Agriculture Reference
In-Depth Information
0
W
=
w
⎧
f
max
D
=
(45)
f
P
W
=
w
f
f
max
The transfer of water between adjacent layers (m s
-1
),
F
i,i+1
, is given by
⎡
⎤
−
B
−
B
⎛
⎞
⎛
⎞
ϑ
ϑ
⎜
⎝
⎟
⎠
⎜
⎝
⎟
⎠
⎢
−
⎥
i
i
+
1
ϑ
ϑ
F
=
K
2
Ψ
s
s
+
1
(46)
⎢
⎥
i
,
i
+
1
ef
s
D
+
D
i
i
+
1
⎢
⎥
⎣
⎦
where B is the Clapp Hornberger [43] constant and
F
ef
is effective hydraulic conductivity (m
s
-1
) between soil layers given by
D
K
+
D
K
(47)
K
=
i
i
i
+
1
i
+
1
ef
D
+
D
i
i
+
1
where
F
i
is the hydraulic conductivity (m s
-1
) of the i
th
soil layer determined by the empirical
formula
2
B
+
3
⎛
ϑ
⎞
i
=
⎜
⎝
⎟
⎠
K
K
(48)
i
sat
,
i
ϑ
s
where
K
sat,i
is the hydraulic conductivity at saturation of the i
th
soil layer. The gravitational
drainage from the bottom soil layer is defined as
2
B
+
3
⎛
ϑ
⎞
()
⎜
⎝
⎟
⎠
F
=
K
3
sin
x
(49)
3
si
ϑ
s
where
x
is the mean slope angle [44,45].
The surface runoff
R
0
is computed as
R
=
P
−
min(
P
,
K
)
(50)
o
1
1
sat
while the subsurface runoff,
R
i
(Figure 4), for each soil layer is calculated using the
expressions
R
=
F
−
min(
F
,
K
)
(51)
1
1
,
2
1
,
2
sat
,
1
R
=
F
−
min(
F
,
K
)
(52)
2
2
,
3
2
,
3
sat
,
2
R
=
F
−
min(
F
,
K
)
.
(53)
3
3
3
sat
,
3
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