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Measuring Soil Bulk Density by Using Vibration-induced Conductivity Fluctuation

Normalized Resistance Fluctuation vs. Soil Bulk Density. Normalized Resistance Fluctuation vs. Soil Bulk Density. 2 10 -4. 2 10 -4. 1.5 10 -4. 1.5 10 -4. 1 10 -4. 1 10 -4. dR s /R s. dR s /R s. Clay, 1000 J kg -1. *. Clay, 1000 J kg -1. *. Clay, 100 J kg -1. *. -.

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Measuring Soil Bulk Density by Using Vibration-induced Conductivity Fluctuation

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  1. Normalized Resistance Fluctuation vs. Soil Bulk Density Normalized Resistance Fluctuation vs. Soil Bulk Density 2 10-4 2 10-4 1.5 10-4 1.5 10-4 1 10-4 1 10-4 dRs/Rs dRs/Rs Clay, 1000 J kg-1 * Clay, 1000 J kg-1 * Clay, 100 J kg-1 * - Measurement circuitry: 5 10-5 5 10-5 Driving resistor To the lock-in amplifier Clay, 100 J kg-1 * Fine sand, 1000 J kg-1 R1 - Fine sand, 1000 J kg-1 ~ * Fine sand, 100 J kg-1 - * Fine sand, 100 J kg-1 Vibration by f2 * * Salinized sand, 100 J kg-1 * * - U1 [f1 =1kHz] U2,1 [f1] U2,2 [f1+2f2 and f1-2f2] Salinized sand, 100 J kg-1 Electrical contact problem (left out of fitting the model) * - Electrical contact problem (left out of fitting the model) 0 100 0 100 * Rs AC Voltage generator Soil resistance (modulated by f2) 0.6 0.8 1.0 1.2 1.4 1.6 Bulk Density (g cm-3) Bulk Density (g cm-3) Ground Resistance fluctuation (dRs) Normalized resistance fluctuation (dRs/Rs) Measurement Errors (Normalized to Signal) 1.2 Instrument noise Within sample SD / Averaged dRs/Rs 0.6 Within treatment 1. Soils Texture Class Clay Fine sand Particle Size Distribution Elec.Cond. (sat.paste) dS m-1 0.6 0.3 Sand Silt Clay --------------%-------------- 0 11.2 97.6 36.7 0.9 52.1 1.5 D D W W D D W W D D D D W W W W Comp1 Comp2 Comp3 Comp4 Comp1 Comp2 Comp3 Comp4 Clay Fine Sand 2. Soil sample treatments • Wet Soil: -1000 J kg-1 (D) and -100 J kg-1 (W) • (clay: 0.20-0.35 cm3 cm-3, sand: 0.03-0.09 cm3 cm-3) • Compacted Soil: used a 1 kg or 3 kg weight • Comp 1 • Comp 2 • Comp 3 • Comp 4 • Salinizied Fine Sand: 2 dS m-1 EC in saturated paste 3 kg Clay (g cm-3) Fine Sand (g cm-3) 0.8 0.8-0.9 0.9-1.0 1.1 1.1-1.2 1.2 1.3 1.5 1 kg Weights compacting the soils by layers 3. Experimental setup for the electrical conductivity measurements 1. Electrode (0.3cm diam. & 7.1 cm length) 1 average 2. Antivibration table 4 2 5 signal 3. Periodic vibrator, 60 Hz 3 4. Lock-in amplifier Time period: 30 sec: U1 & U2,1 90 sec: U2,2,0 & U2,2,vibr 5. Software for averaging signal over time Measuring Soil Bulk Density by Using Vibration-induced Conductivity Fluctuation A. Sz. Kishné, C. L.S. Morgan Dept. of Soil and Crop Sciences, Texas A&M University, College Station, TX, USA L. B. Kish Dept. ofElectrical and Computer Engineering, Texas A&M University, College Station, TX, USA Results Justification Quantification of soil bulk density under field conditions is time consuming and difficult. A novel method for quantifying soil bulk density in the field involves using recent advances in fluctuation and noise research. Theoretically this method can be made independent of soil salinity and moisture. Possible application of this method is explored. Objectives • Introduce a new, non-destructive method for measuring soil bulk density by exposing soils to a periodic vibration and measuring the vibration-induced conductivity fluctuation (VICOF) • Test the measurement principles on packed soil samples • Test the effect of salinity and moisture on VICOF at current measurement setup Principles * * 0.6 0.8 1.0 1.2 1.4 1.6 Materials and Methods Discussion and Conclusions • A curvilinear, inverse relationship exists between normalized vibration-induced resistance fluctuation and soil bulk density that is specific for soil texture. • Soil moisture and salinity effects this relationship at 60 Hz vibration frequency, but these effects may be eliminated by taking measurements at multiple frequencies. • Instrument noise increases with increasing bulk density. Error ratio and soil-electrode contact is expected to improve with the use of a blade-shaped compared to the current needle-shaped electrode. • According to preliminary result, salinity (2 dS m-1) has a minimal effect on the measurement References • Kish,L.B., C.L.S. Morgan and A.Sz. Kishné (2006). Vibration-induced Conductivity Fluctuation Testing of Soils. Fluctuations and Noise Letters. Submitted • Texas A&M University patent disclosure (November 2005) Acknowledgements • Appreciation is expressed to Dr. K. McInnes and Dr. T. Hallmark(TAMU) for their valuable suggestions for compacting and salinizing the soil samples, respectively. • The research was supported by Texas Agricultural Experiment Station.

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