Evaluation of Effective Parameters for Water Uptake through Roots of Trees

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Evaluation of Effective Parameters for Water
Uptake through Roots of Trees
Hedieh Salamat. University of Urmia, Department
of water engineering, Parastoo Parsamehr.
University of Urmia, Department of water
engineering, Dr.Sina Besharat. University of
Urmia, Department of water engineering,
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• Root water uptake is an important process of
  soil, water and plant relationship and is an
  important component for water balance in the
  field .
• The objective of this paper is to evaluate the
  effective parameters for water uptake through
  roots of trees in order to improve soil water
  content and increase water use efficiency by
  controlling the more important parameters as
  Transpiration.
• among the effective parameters in root water
  uptake, Transpiration (T) had an considerable
  effect.Good measurements of E can be obtained
  using micro-lysimetry, and have been used
  successfully in field studies limited to single
  drying cycles of a few weeks following irrigation
  .
• here we have used the results of one of these
  studies that have been taken in a wheather
  station of california and actual T was estimated
  through governing equations The results showed
  that with the optimised root water uptake
  parameters, simulated and measured Transpiration
  were in excellent agreement for all root Water
  uptake models .this results were used to improve
  soil water content and increase water use
  Efficiency.

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• Water has been labelled blue gold and blue
  gold is destined to be the critical issue of the
  21st Century Water is the lifeblood of plants It
  is the most important factor controlling plant
  growth .
• A plant gets its water by root uptake. Irrigation
  is required when the soil is incapable of
  supplying the plants needs for water.
• From a hydrological perspective, water uptake by
  root systems and their spatial distribution may
  exert a large degree of control on the water
  fluxes to the atmosphere and the groundwater. For
  an improved understanding of the magnitude of
  these fluxes, accurate estimates of the temporal
  and spatial root water uptake patterns are
  needed. In order to optimize water uptake through
  roots, effective parameters should be determined.
• In this paper we have mentioned 3 parts
• 1.effective parameters in root water uptake ,
• 2. measurements and estimation methods ,
• 3. more important parameters according to
  models.
• Water absorption by plant roots from the soil is
  determined by 3 main factors
• 1. the soil properties
• 2. the root system architecture, here considered
  as a network of absorbing
• 3. the absorption capability of roots dependent
  on the soil root interface and the resistance of
  the root to water transfer

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Materials and methods
2.1. Used governing equations and materials
According to researches , the most important
equation that represents the water extraction of
the entire root system is Richards equation
which include a sink term describing transient
multi dimensional water flow that can be
expressed as
(1)
Where (s) is the volumetric water content (L3
L3), K is the unsaturated hydraulic conductivity
tensor (L T-1), h (L)is the soil water matric
head, z (L) is the depth which is included for
vertical flow only, and S is the volumetric sink
term (L3 L-3T-1),representing root water uptake
as a function of both space and time.
(2)
( z) is a shape factor describing the spatial
distribution of potential root water uptake with
depth, Zm (L) is the maximum rooting depth, and
pz and z (L) are empirical parameters. These
parameters are included to provide for zero root
water uptake at z Zm to account for asymmetrical
root water uptake with depth and also to allow
for a maximum root water uptake rate at any
depth, Z0(0lt Z0 lt Zm). The asymmetry in root
water uptake with soil depth is determined by the
ratio between pz for z ltz and the pz value for
z gt z.
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or
(3)

• Denoting the normalized root water uptake Sm (L3
  L -3T-1) as the volume of water extracted per
  unit volume of soil One dimensional description
  Denoting the normalized root water uptake Sm (L3
  L -3T-1) as the volume of water extracted per
  unit volume of soil One-dimensional description

(4)
To provide for root water uptake under
water-stressed conditions, a soil water stress
response function was included
(5)
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• Where h is the soil water matric head at a
  particular spatial location, h50 (L) is the soil
  water pressure head at which root water uptake
  rate is reduced by 50, and p (dimensionless) is
  a fitting parameter
• Finally, the actual root water uptake rate at any
  particular spatial location can be calculated
  from

(6)
(7)
Tpot ET tree -Es

Where S (h, x, y, z) (T-1) is the actual root
water uptake and Es (L T1) denotes soil
evaporation. ETtree defines the potential ET by
trees and is computed from the product of Kc and
ET0, where Kc is the crop coefficient
(dimensionless), and ET0 (L T-1) is the reference
evapotranspiration. Hence the actual
transpiration rate Ta can be computed from
(8)
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• The unsaturated hydraulic properties for all
  three models are defined by

(9)
(10)
where ?s (L3 L-3) is the saturated water
content, (L3 L-3) is the residual water
content, (L-1) and n (dimensionless) are curve
shape parameters, and Ks (LT-1) denotes the
saturated hydraulic conductivity. considering a
one-dimensional steady state flow in a series
network, the liquid flow equation is
(11)
Where T (cm s-1) is the transpiration rate,
hsoil, hroot and hleaf (cm) are pressure heads in
the soil, at the root surface and in the leaves,
respectively, Rsoil and Rplant (s) are liquid
flow resistances of the soil and the plant .
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• Gardners equation, using the modern terminology
  of matric pressure potential instead of suction,
  is

(12)
Where ?b (MPa) is the matric pressure potential
midway between two roots, ?a (MPa) the matric
pressure potential at the plant rootsoil
boundary, q the volume of water taken up per unit
length of root per unit time(m-3m-1s-1), and k is
the hydraulic conductivity of the unsaturated
soil(m2s-1Mpa-1). Another formula was the The
volumetric flux vz is given by Darcys law
(13)
Where k is hydraulic conductivity (cm d-1) and h
is soil water pressure head (cm).
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• Commonly it is assumed that, in an
• unsaturated soil, water flows only in the
  vertical direction z.water flow through roots (
  vroots ) can be calculated as the measured total
  flow through soil and roots ( vtotal ) diminished
  with the calculated flow through the soil (
  vsoil).

(14)
2.2. Parameters and measurement methods
According to our studies the most effective
factor in water uptake through roots of trees is
transpiration, but there is no direct measurement
of the transpiration of apple tree was available
Figure 1 presents the daily estimated boundary
conditions as function of time during the
monitoring period.
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Figure 1. Soil surface boundary conditions during
simulation period (Time 0 corresponds with
September 13).
3. Results and Discussion In water-limited
ecosystems, transpiration can be determined from
two limiting conditions uptake limited by
available energy when soil moisture is plentiful
and by available water under water-stressed
conditions. The conceptual model can be
represented by the following function
(15)
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In Eq. (15) Tact represents total plant uptake as
volume per area per time, Tpot is the potential
rate of daily transpiration, and Umax is the
maximum uptake possibly the plant.Local uptake
from a soil layer of thickness Dz is given by
(16)
Where u (z, t) is local uptake as volume of water
per area per time, W is the soilwater potential
as a function of depth and time, and Wp is the
plant potential . R1 is saturation dependent
Resistance that depends on soil and root
characteristics (saturation is defined as volume
of water per volume of void space), and R2 is
vegetation dependent. Therefore, integrating Eq.
(16) over the root zone (depth ZR) with Wp set
equal to Ww and combining with Eq. (15) gives an
expression for daily transpiration
(17)
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• Fig. 2 presents the maximum rate of local uptake
  versus local saturation for a wood yspecies
  (Burkea africana) in an African savanna.

Fig. 2. Local uptake, relative to Tpot per unit
of roots, as a function of local saturation in
the soil when Wp Ww. The three curves represent
plants with varying degrees of compensation
ability. For this sandy soil, Sw 0.03, S
0.11 and Sfc 0.30.
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• Fig. 3 shows the relationship between average
  root-zone saturation and total plant uptake as a
  soil dries out. Curves are presented for five
  different initial conditions, ranging from the
  entire root zone being at field capacity to just
  the top 20 of the roots being wetted.

Fig. 3. Relationships between transpiration and
average root-zone saturation. d is the fraction
of the soil column initially wetted to field
capacity. (a) Drying curves for vegetation with c
2.0, (b) drying .curves for vegetation with c
1.33.
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The main objective of this paper is to evaluate
effective parameters of root water uptake and the
effect of optimization of these parameters in our
environment and ecologic systems. Finally,
according to governing equations that were
mentioned in part 2, and the relationship between
soil-water-plant the importance of these
parameters can be understood.
4. Conclusions The water uptake through roots is
a function of both space and time. Plant root
systems show a remarkable ability to adapt to
soil depth and to changes in availability of
water and nutrients and the chemical properties
(e.g. ,salinity) in soils. From our researches
we would be able to determine important
parameters efficiency water uptake through root
of trees to control the most important of them
for optimized growth of tree and even other
plants.