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

Measurement Principles Driving resistor To the lock-in amplifier R 1 Vibration by f 2 U 1 [ f 1 ] U 2,1 [ f 1 ] ~ R s U 2,2 [ f 1 +2f 2 and Voltage generator Soil resistance f 1 -2f 2 ] (modulated by 2 f 2 ) Ground Fluctuation Normalized Fluctuation " % U 2,2 U 2,1 = 2 U 2,2 U 2,1 dR s dR s = 2 R 1 (1 + ) 1 + $ ' U 1 ! U 2,1 U 1 ! U 2,1 R s U 2,1 U 1 ! U 2,1 # &

Measurement Principles Fourier amplitude spectrum of measured voltage 1000 Hz c ( f ) ~ 0.5 V It needs a lockin amplifier 880 Hz 1120 Hz few microV few microV f

Objectives To improve the normalized VICOF signal to noise ratio • by using blade shape electrodes; To reduce the effect of salinity (and perhaps moisture) • on 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 Longitudinal Transversal

Soils Texture Class Sand Silt Clay Organic C Electr.Conductivity (saturated paste) ---------------------------%----------------------- dS m -1 Fine Sand 0.7 0.4 89.5 8.4 2.1 Soil sample treatments Wetness : -1500 J kg -1 ( Dry ) and -33 J kg -1 ( Wet ) (2%, 4% water on dry mass basis ) 3 kg Compaction : used a 1 kg or 3 kg weight Dry Wet g cm-3 g cm-3 1 kg 1.25 1.12 Comp 1 1.30 1.19 Comp 2 Comp 3 1.36 1.30 Comp 4 1.54 1.48 Salinizied F.Sand : 16 dS m -1 EC in saturated paste Weights compacting the soils by layers

Blade vs. Cylindrical Electrodes Set-up Noise, Normalized to Signal 1 Cylindrical Blades 0.8 0.6 0.4 0.2 0 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 o n

Measured Longitudinal & Transversal VICOF 0.0001 0.0001 2 = 0.70 Longitudinal y = 0.00026 - 0.00016x R Non-saline, dry Transversal 2 = 0.76 y = 0.00023 - 0.00014x R Non-saline, wet 2 = 0.19 y = 3.8e-05 - 2.12e-05x R Saline, wet 2 = 0.04 y = 2.07e-05 - 9.43e-06x R -5 8 10 -5 2 = 0.31 8 10 y = 3.71e-05 - 2.24e-05x R 2 = 0.01 y = 6.8e-06 - 1.57e-06x R -5 6 10 -5 6 10 -5 4 10 -5 4 10 -5 2 10 -5 2 10 0 0 1.1 1.2 1.3 1.4 1.5 1.6 1.1 1.2 1.3 1.4 1.5 1.6 -3 Bulk Density, g cm -3 Bulk Density, g cm 1.6 Transversal/Longitudinal 1.4 1.2 1 0.8 0.6 0.4 0.2 0 1.1 1.2 1.3 1.4 1.5 1.6 -3 Bulk Density, g cm

Conclusions Blade-shape electrodes outperformed the ! cylindrical electrode. According to the theory and simulation, the ratio of ! dR s,T /Rs and dR s,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.