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low transpiration, low root density
low transpiration, medium root density
1
1
0
0
0
0
h
mean
-40
-80
-120
-160
-40
-80
-120
-160
h
mean
h
root
h
root
0
10
20
30
40
0
10
20
30
40
time, d
time, d
high transpiration, low root density
low transpiration, high root density
1
1
0
0
0
0
h
mean
-40
-80
-120
-160
-40
-80
-120
-160
h
mean
h
root
h
root
0
10
20
30
40
0
10
20
30
40
time, d
time, d
high transpiration, high root density
high transpiration, medium root density
1
1
0
0
0
0
-40
-80
-120
-160
-40
-80
-120
-160
h
mean
h
mean
h
root
h
root
0
10
20
30
40
0
10
20
30
40
time, d
time, d
Figure 6.5
Simulated pressure head at root surface (
h
root
), mean pressure head (
h
mean
)
and relative transpiration as a function of time for low and high potential transpira-
tion rates and low, medium and high root density in a clay soil (De Jong van Lier
et al.,
2006
).
plant and soil that occur during heterogeneous dry conditions in the root zone, and to
verify simplifying assumptions in operational ecohydrological models.
Macroscopic Models
In the macroscopic approach, the entire root system is viewed as a diffuse sink that
penetrates each soil layer uniformly, though not necessarily with a constant strength
throughout the root zone. This approach disregards the low patterns toward indi-
vidual roots and thus avoids the geometric complications involved in analyzing the
distribution of luxes and potential gradients on a microscale. The major shortcom-
ing of the macroscopic approach is that it is based on gross spatial averaging of the
pressure and osmotic heads. The approach does not consider the decrease in pressure
head and increase in concentration of salts at the immediate periphery of absorbing
roots. However, the macroscopic approach has been very useful to model root water
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