Transcript Slide 1
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. of Electrical 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. Normalized Resistance Fluctuation vs. Soil Bulk Density 2 10-4 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) 2. Test the measurement principles on packed soil samples 3. Test the effect of salinity and moisture on VICOF at current measurement setup dRs/Rs 1. 1.5 10-4 Principles Driving resistor Measurement circuitry: To the lock-in amplifier R1 10-5 5 U2,1 [f1] ~ Rs Soil resistance (modulated by f2) U2,2 [f1+2f2 and f1-2f2] 0 U1 - U 2,1 (1+ U 2,1 U1 - U 2,1 ) 1. Soils Texture Class Normalized resistance fluctuation (dRs/Rs) U 2, 2 U 2,1 dRs 1 2 Rs U 2,1 U1 U 2,1 Particle Size Distribution Sand Silt Clay --------------%-------------11.2 36.7 52.1 97.6 0.9 1.5 Clay Fine sand 1.0 - - - - 1.2 1.4 1.6 Bulk Density (g cm-3) Materials and Methods * 0.8 Clay, 1000 J kg-1 Clay, 100 J kg-1 Fine sand, 1000 J kg-1 Fine sand, 100 J kg-1 Salinized sand, 100 J kg-1 Electrical contact problem (left out of fitting the model) - 100 0.6 Elec.Cond. (sat.paste) dS m-1 0.6 0.3 SD / Averaged dRs/Rs dRs = 2R1 U 2,2 * * ** Ground Resistance fluctuation (dRs) * * * * Vibration by f2 U1 [f1 =1kHz] AC Voltage generator 1 10-4 Measurement Errors (Normalized to Signal) 1.2 0.6 Instrument noise Within sample Within treatment 0 D W D W D W D W D W D W D W D 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 Clay (g cm-3) 0.8 0.8-0.9 0.9-1.0 1.1 Comp 1 Comp 2 Comp 3 Comp 4 3 kg Fine Sand (g cm-3) 1.1-1.2 1.2 1.3 1.5 • Salinizied Fine Sand: 2 dS m-1 Discussion and Conclusions 1 kg EC in saturated paste Weights compacting the soils by layers 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 3. Experimental setup for the electrical conductivity measurements 1. Electrode (0.3cm diam. & 7.1 cm length) 1 4 2 3 4. Lock-in amplifier 5. Software for averaging signal over time 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) average 2. Antivibration table 3. Periodic vibrator, 60 Hz signal 5 Time period: 30 sec: U1 & U2,1 90 sec: U2,2,0 & U2,2,vibr 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.