Vibration-Induced Conductivity Fluctuation Measurement for Soil Bulk - - PowerPoint PPT Presentation

Vibration-Induced Conductivity Fluctuation Measurement for Soil Bulk Density Analysis

Andrea Sz. Kishné and Cristine L.S. Morgan

• Dept. of Soil and Crop Sciences, Texas A&M Univ.

Hung-Chih Chang and László B. Kish*

• Dept. of Electrical and Computer Eng., Texas A&M Univ.

*speaker

Background Soil bulk density

• applications to many soil studies: e.g. estimating

water budgets, nutrient availability, soil carbon sequestration in the plant root zone.

• varies across landscapes;
• its measurement is time consuming and difficult in

field conditions.

• volumetric ring, paraffin sealed clod, gamma ray

attenuation techniques, TDR

!Background, continued

• A novel method was introduced to measure soil

porosity and bulk density non-destructively.

• Normalized vibration-induced conductivity

fluctuation (VICOF), a mechano-electrical-transport method, was demonstrated on clay and fine sand soils using cylindrical electrodes (2006).

Measurement Principles

Electrodes Soil container Soil Forced oscillations Antivibration table Vibrator sin(!t +") !"(t) # a(t) # sin($t +%) First harmonic of !"(t) is at 2#

Measurement Principles

Ground

To the lock-in amplifier

Soil resistance (modulated by 2 f2) R1 U1 [f1] Rs

~

U2,1 [f1] U2,2 [f1+2f2 and f1-2f2] Voltage generator Driving resistor Vibration by f2

dRs Rs = 2 U2,2 U2,1 1+ U2,1 U1 !U2,1 " # $ % & ' dRs = 2R1 U2,2 U1 !U2,1 (1+ U2,1 U1 !U2,1 )

Fluctuation Normalized Fluctuation

Measurement Principles

c( f ) f

1000 Hz ~ 0.5 V 1120 Hz few microV 880 Hz few microV

It needs a lockin amplifier Fourier amplitude spectrum of measured voltage

Objectives

• To improve the normalized VICOF signal to noise ratio

by using blade shape electrodes;

• To reduce the effect of salinity (and perhaps moisture)
• n the determination of bulk density by positioning the

blade electrodes longitudinally and transversally to the direction of the induced vibration, and calculating their ratio.

• Such data are independent from the strength of

vibration (in the elastic limit), which is a further advantage.

Measurement Set-up

Positioning the Electrodes

Transversal Longitudinal

Soils

1 kg 3 kg

Weights compacting the soils by layers Wetness: -1500 J kg-1 (Dry) and -33 J kg-1 (Wet) (2%, 4% water on dry mass basis) Compaction: used a 1 kg or 3 kg weight Comp 1 Comp 2 Comp 3 Comp 4 Salinizied F.Sand: 16 dS m-1 EC in saturated paste

Soil sample treatments

Dry Wet

g cm-3 g cm-3

1.25 1.12 1.30 1.19 1.36 1.30 1.54 1.48

89.5 8.4 2.1

• --------------------------%-----------------------

Texture Class Fine Sand Electr.Conductivity (saturated paste) dS m-1 0.4 Sand Silt Clay Organic C 0.7

Blade vs. Cylindrical Electrodes

0.2 0.4 0.6 0.8 1

Set-up Noise, Normalized to Signal

Cylindrical Blades Dry Wet Dry Wet Dry Wet Dry Wet Compact 1 Compact 2 Compact 3 Compact 4 Treatments

Simulation

V i b r a t i

• n

Measured Longitudinal & Transversal VICOF

2 10

• 5

4 10

• 5

6 10

• 5

8 10

• 5

0.0001 1.1 1.2 1.3 1.4 1.5 1.6

Longitudinal

Non-saline, dry Non-saline, wet Saline, wet y = 0.00026 - 0.00016x R

y = 3.8e-05 - 2.12e-05x R

y = 3.71e-05 - 2.24e-05x R

Bulk Density, g cm

• 3

2 10

• 5

4 10

• 5

6 10

• 5

8 10

• 5

0.0001 1.1 1.2 1.3 1.4 1.5 1.6

Transversal

y = 0.00023 - 0.00014x R

y = 2.07e-05 - 9.43e-06x R

y = 6.8e-06 - 1.57e-06x R

Bulk Density, g cm

• 3

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.1 1.2 1.3 1.4 1.5 1.6

Transversal/Longitudinal

Bulk Density, g cm

• 3

Conclusions

!

Blade-shape electrodes outperformed the cylindrical electrode.

!

According to the theory and simulation, the ratio of dRs,T/Rs and dRs,L/Rs is independent of moisture and salinity effects.

Conclusions, continued

!

There is an inverse correlation between the bulk density and normalized VICOF for both longitudinal and transversal cases shown by measurements on dry fine sand.

!

More studies are planned to improve the electrode material and the vibration method. Fundamental studies of the vibration effect on the mechano- electrical soil responses are needed.