Measuring soil hydrological properties in different climatic and pedological conditions

Marco Bittelli a, Markus Flury b, Paola Rossi Pisa a,

Kurt Roth c and Fiorenzo Salvatorelli a

a Department of Agro-Environmental Science and Technology, University of Bologna, Italy.B Department of Crop and Soil Sciences, Washington State University, Pullman, WA, USA.c Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany.

Also thank to:

Gaylon Campbell Vittorio Marletto Franco Zinoni Gernot Kasper Andrea Pasquali William Pratizzoli Francesca Ventura

Soil Water Content

It controls the partitioning of radiation into sensible and latent heat

It couples the soil compartment to the atmosphere, in the hydrological cycle

It determines the partition of precipitation into runoff and infiltration

It determines soil solute transport (breakthrough curve)

Measurements at different scales

Point Scale (Gravimetry, Gypsum blocks, Neutron Probes, FDR, TDR and other).

Field Scale (Ground Penetrating Radar, Electrical Resistivity).

Regional Scale (Airborne Microwave Radiometry)

Global Scale (Satellite Passive Microwave Radiometry- Satellite Aqua)

Point Scale

1) Measurement in the Arctic

2) Measurement in the Italian Apennines

3) Measurement in the Italian Po valley

(1) ARCTIC(1) ARCTIC::Liquid water and ice content in frozen porous media

Permafrost covers about one fifth of global land areas. It is a relevant terrestrial system because it plays an important role in earth surface temperature and into the calibration of climate models.

Soil freeze-thaw status influence plant growth, carbon exchange between the land and the atmosphere and surface and subsurface hydrology.

Permafrost studies

Experimental station:

- Weather Station- Soil temperature- Soil heat flux

Liquid Water and Ice Content ?

Experimental Station (Svalbard)

From: Ippisch, O. , 2001: Coupled Transport in Natural Porous Media. Ph.D. Dissertation, University of Heidelberg, Germany

Soil

Example of the problem : 3 phase system

= soil minerals

= liquid water

= ice

= liquid water

= soil minerals + ice

EM field

TDR

“ObjectMeasurement”

w

w

i

s

i+s

Dielectric permittivity and relaxation of polarmolecules (H2O)

+ ++ + ++

- --

-

+

H2O

0.01 0.1 1 10 100

Frequency (GHz)

Die

lect

ric

pe

rmitt

ivity

20

40

60

100

80

25 C

= ’- i ’’

Hypothesis

Ice undergoes relaxation at lower frequency (1 to 10 kHz), compared to liquid water.

Ice permittivity at low frequency is higher than at higher frequency (relaxation).

By measuring bulk dielectric permittivity at two different frequencies we can detect the ice dielectric

fingerprint

Measured Ice permittivity

Theory : dielectric mixing model

1991) al., et Roth particle, soil of ondistributi random0.5( parameter lgeometrica

porosity

content ice volumetric

content air volumetric

content waterliquid volumetric

kHz) 100~ of f at 3.2 kHz; 100 f 0 for 4-(100ty permittivi dielectric ice

10)-(3ty permittivi dielectric mineralsdry

(1.005)ty permittivi dielectric air

85)-(75ty permittivi dielectric water

typermittivi dielectric bulk

i

a

w

i

s

a

w

b

Tf

Tf

Tf

Tf

Tf

),(

),(

),(

),(

),(

Theory: system of equations

Solution

,)(

)(

1,1,

2,2,,

sa

sasa

,)(

)(

1,1,

2,2,,

ai

aiai

,)(

)(

1,1,

2,2,,

al

alal

)(

)(

1,1,

2,2,

,si

si

si

Experimental setup (Kirchoff Institute of Physics, Heidelberg, Germany)

Results: dielectric Permittivity vs. Temperature

Results: Ice and Liquid Water Content

Bittelli M., M. Flury and K. Roth, Use of Dielectric Spectroscopy to Estimate Ice Content in Frozen Porous Media. Water Resources Research, Vol. 40, W04212, doi:10.129/2003WR002343.

(2) APENNINES:(2) APENNINES:Liquid water content in Clay deposits

The Italian Apennine mountain chain is characterized by chaotic undifferentiated clay deposits.

Polarization and high dielectric conductivity in samples with high clay content causes dispersion of the electromagnetic wave energy and therefore could prevent measurement.

Technical and theoretical issues needs to be considered to successfully measure soil water content in these conditions.

Aqua Modis

Experimental site

TDR probe Campbell CS610

Effect of high electrical conductivity on the TDR waveform

What to do

c

L2st

1) Reduction of the cable length

2) Reduction of the probe length

3) Covering the probe with plastic material

4) Frequency analysis via Fourier Transformation and separation of the real and imaginary component

(3) PO VALLEY:(3) PO VALLEY:Liquid water content in Alluvial Sand Deposits

The Italian Po Valley is often characterized by Alluvial deposits (conglomerates, gravel, sand)

In these conditions, dielectric conductivity is usually low because sand have low specific surface area and low ions contents.

If the area is under intense agricultural activities, where fertilizations are performed, high electrical conductivity can be due to high soil ionic concentration.

Soil Profile

Paleo A horizon

TDR installation

sand

TDR 100, CR10X and battery charged by a solar panel

Conclusions and future work

TDR is becoming an increasingly utilized methodologies for soil water content measurement.

Its popularity is due to several reasons including time continuous data acquisition, precision, low cost, no risk for

the operator. Knowledge of the dielectric response of the material under

investigation is needed, especially when operating on highly conductive material.

Soil Water Content studies at different scales are needed to elucidate the scale dependent features of these methodologies and provide input data to regional and global scale models.

Thank you for your attention