Developing New Electrical Conductivity Technique for Measuring Soil Bulk Density

Transcription

1 Developing New Electrical Conductivity Technique for Measuring Soil Bulk Density 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 Engineering, Texas A&M Univ.

2 Background Soil bulk density applications (e.g. estimating water budgets, nutrient availability, soil carbon sequestration) varies across landscapes; measurements: volumetric ring, paraffin sealed clod, gamma ray attenuation techniques, TDR Time consuming and difficult in field conditions.

3 Background, continued Novel method, introduced to measure soil porosity and bulk density non-destructively. Kish et al. (2006) Vibration-induced conductivity fluctuation (VICOF) testing of soils. Fluctuation and Noise Letters 6(4) L359-L365. Normalized vibration-induced conductivity fluctuation (VICOF) demonstrated on clay and fine sand soils using cylindrical electrodes. Kishné et al. (2006) Measuring soil bulk density using vibration-induced conductance fluctuation (VICOF). Poster, WCSS 18 th Philadelphia, PA.

4 Measurement Set-up

5 Positioning the Electrodes Longitudinal Electrodes L = 7 cm W= 2 cm D = 0.15 cm Transversal Kishné, A.Sz., C.L.S. Morgan, H-C. Chang, and L.B. Kish (2007) Vibration-induced conductivity fluctuation measurement for soil bulk density analysis. Fluctuation and Noise Letters, accepted.

6 Objectives To reduce the effect of moisture and salinity on the EC determination of bulk density by using VICOF with blade electrodes. To test the normalized VICOF measurement for bulk density determination on clay, sand and salinized sand soils.

7 Soils Texture Fine Sand (Padina) Clay (Houston Black) Sand Silt Clay Organic % C Electr.Conductivity (saturated paste) ds m Treatments Wetness: Wet (-33 J kg -1 ) clay: 40 % sand: 4 % Dry (-1500 J kg -1 ) clay: 27 % sand: 3 % 3 kg Compaction: Comp 1 Comp 2 Comp 3 Comp 4 Clay wet Clay dry Sand wet Sand dry g cm kg Salinization (Sand): 16 ds m -1 EC in saturated paste Compacting the soils by layers

8 Measurement Principles Driving resistor R 1 To the lock-in amplifier ~ U 1 Voltage generator R s Vibration by f 2 Soil resistance (modulated by 2 f 2 ) U 2,1 U 2,2 ±2 f 2 Ground

9 Measurement Principles Driving resistor R 1 To the lock-in amplifier ~ U 1 Voltage generator R s Vibration by f 2 Soil resistance (modulated by 2 f 2 ) U 2,1 U 2,2 ±2 f 2 R s = R 1 U 1 U 2,1 U 2,1 Ground

10 Measurement Principles Driving resistor R 1 To the lock-in amplifier ~ U 1 Voltage generator R s Vibration by f 2 Soil resistance (modulated by 2 f 2 ) U 2,1 U 2,2 ±2 f 2 R s = R 1 U 1 U 2,1 U 2,1 Ground Fluctuation dr s = 2R 1 U 2,2 U 1 U 2,1 (1 + U 2,1 U 1 U 2,1 )

11 Measurement Principles Driving resistor R 1 To the lock-in amplifier ~ U 1 Voltage generator R s Vibration by f 2 Soil resistance (modulated by 2 f 2 ) U 2,1 U 2,2 ±2 f 2 R s = R 1 U 1 U 2,1 U 2,1 Ground Fluctuation dr s = 2R 1 U 2,2 U 1 U 2,1 (1 + U 2,1 U 1 U 2,1 ) Normalized Fluctuation dr s = 2 U 2,2 1 + R s U 2,1 U 2,1 U 1 U 2,1

12 Results VICOF dr soil (longitudinal), Ohm clay, dry clay, wet non-saline sand, dry non-saline sand, wet salinized sand, dry salinized sand, wet Rs R soil, Ohm

13 VICOF vs. Soil Resistance dr soil (longitudinal), Ohm VICOF Rs R soil, Ohm clay, dry clay, wet non-saline sand, dry non-saline sand, wet salinized sand, dry salinized sand, wet dr soil /R soil (longitudinal) Normalized VICOF Rs R soil, Ohm

14 Normalized VICOF vs Bulk Density dr soil /R soil (longitudinal) Bulk Density, g cm -3 Bulk Density, g cm -3 clay, dry r 2 =0.22 clay, wet r 2 =0.77 non-saline sand, dry r 2 =0.78 non-saline sand, wet r 2 =0.20 saline sand, wet r 2 =0.37

15 Conclusions Normalized VICOF: promising theory and experiments to assess bulk density of soils with reduced effect of moisture and salinity; Inverse correlation between soil bulk density and the normalized VICOF was clear on fine sand at J kg -1 moisture conditions and clay at -33 J kg -1 moisture; Contact between the electrodes and soil needs improvement.

16 Research to Be Continued Improving the electrode - soil contact, and the vibration method; Basic research for relating the conductivity fluctuation modulated by vibration to the soil matrix, adsorbed cations, soil solution and their exchange processes at microscopic scale.

17 Acknowledgement The research was supported by Texas Agricultural Experiment Station. Dr. Kevin McInnes (suggestions in the soil compaction), Dr. Thomas Hallmark (guidelines in salinization), Mr. Richard Epting (blade electrodes, electrode insertion guide).

18 Questions? Comments?