Saturday, 15 July 2006

Measuring Soil Bulk Density Using Vibration-induced Conductance Fluctuation (VICOF).

Andrea Sz. Kishné1, Cristine L.S. Morgan1, and László B. Kish2. (1) Texas A&M Univ, Dept of Soil and Crop Sciences, College Station, TX 77843-2474, (2) Texas A&M Univ, Dept of Electrical and Computer Engineering, College Station, TX 77843-3128

Soil bulk density is a spatially variable soil property characterizing soil structure and compaction that influences water movements, availability of nutrients and chemical applications. In the field it is difficult to determine with excavation of a soil sample or with neutron-gamma surface gauge. A new non-destructive method is suggested for field and laboratory use and experimentally demonstrated for measuring soil bulk density by conductance modulation (fluctuation) measurements of soils while exposed to periodic vibration. The relative fluctuation of the conductivity is expected to depend very weakly on the actual electrical conductivity of soil water. In the laboratory, soil samples including a smectitic clay and sand were prepared to two moisture conditions and three density levels in replicates. The AC electrical conductance response of soils was measured with a lock-in amplifier while applying periodic vibration. The density modulation induced by the vibration produces periodic conductivity fluctuation. This conductance fluctuation was analyzed by measuring the two side-peaks in the spectra representing some of the combination frequencies of the AC voltage and the mechanical vibration. The theory and results of the experiment will be presented and discussed.

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