Evaluation of Effective Evaluation of Effective Parameters for Water Parameters for Water

Uptake through Roots of Uptake through Roots of TreesTrees

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,

Root water uptake is an important process of soil, water and plant Root water uptake is an important process of soil, water and plant relationship and is an important component for water balance in the fieldrelationship and is an important component for water balance in the field. .

The objective of this paper is to evaluate the effective parameters for water 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 uptake through roots of trees in order to improve soil water content and increase water use efficiency by controlling the more important increase water use efficiency by controlling the more important parameters as Transpirationparameters as Transpiration..

among the effective parameters in root water uptake, Transpiration (T) had among the effective parameters in root water uptake, Transpiration (T) had an considerable effect.Good measurements of an considerable effect.Good measurements of E E can be obtained using can be obtained using micro-lysimetry, and have been used successfully in field studies limited micro-lysimetry, and have been used successfully in field studies limited to single drying cycles of a few weeks following irrigationto 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 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 a wheather station of california and actual T was estimated through governing equations The results showed that with the optimised root governing equations The results showed that with the optimised root water uptake parameters, simulated and measured Transpiration were in water uptake parameters, simulated and measured Transpiration were in excellent agreement for all root Water uptake models .this results were excellent agreement for all root Water uptake models .this results were used to improve soil water content and increase water use Efficiencyused to improve soil water content and increase water use Efficiency..

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 A plant gets its water by root uptake. Irrigation is required when the soil is incapable of supplying the plant’s needs for waterincapable of supplying the plant’s needs for water..

From a hydrological perspective, water uptake by root systemsFrom a hydrological perspective, water uptake by root systems and their spatial and their spatial distribution may exert a large degree of control on the water fluxes to the distribution may exert a large degree of control on the water fluxes to the atmosphere and the groundwater. For an improved understanding of the atmosphere and the groundwater. For an improved understanding of the magnitude of these fluxes, accurate estimates of the temporal and spatial magnitude of these fluxes, accurate estimates of the temporal and spatial root water uptake patterns are needed. In order to optimize water uptake root water uptake patterns are needed. In order to optimize water uptake through roots, effective parameters should be determinedthrough roots, effective parameters should be determined..

In this paper we have mentioned 3 parts: 11..effective parameters in root water uptakeeffective parameters in root water uptake , ,

22 . .measurements and estimation methodsmeasurements and estimation methods, , 33 . .more important parameters according to modelsmore important parameters according to models..

Water absorption by plant roots from the soil is determined by 3 main factors:

1 .the soil properties2 .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

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)

Materials and methods:

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(0<= Z0 <= Zm). The asymmetry in root water uptake with soil depth is determined

by the ratio between pz for z <=z* and the pz value for z > z.*

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 Denoting the normalized root water uptake Sm Sm ((LL3 3 LL -3T-1) as the volume of water extracted per unit volume of soil One-dimensional description -3T-1) as the volume of water extracted per unit volume of soil One-dimensional description

or )3(

)4 (

To provide for root water uptake under water-stressed conditions, a soil water stress response function was included

)5 (

Where hWhere h is the soil water matric head at a particular spatial location, h50 (L) is 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 the soil water pressure head at which root water uptake rate is reduced by 50%, and p50%, and p (dimensionless) is a fitting parameter(dimensionless) is a fitting parameter

Finally, the actual root water uptake rate at any particular spatial location can be Finally, the actual root water uptake rate at any particular spatial location can be calculated fromcalculated from::

(7)

(6)

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)

The unsaturated hydraulic properties for all three models are defined by

(9)

(10)

where θs (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.

Gardner’s equation, using the modern terminology of matric pressure Gardner’s equation, using the modern terminology of matric pressure potential instead of suction, ispotential instead of suction, is

(12)

Where ψb (MPa) is the matric pressure potential midway between two roots, ψa (MPa) the matric pressure potential at the plant root–soil 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 Darcy’s law:

(13)

Where k is hydraulic conductivity (cm d-1) and h is soil water pressure head (cm).

Commonly it is assumed that, in anunsaturated 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.

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)

In Eq. (15) Tact represents total plant uptake as volume per area per time, Tpot is the 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.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 byLocal 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 soil–water 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)

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.

•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.

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.