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Time Domain Reflectometry Probe for Simultaneous Measurement of Soil Matric Potential and Water Content

^a Department of Agronomy, Iowa State University, Ames, IA 50011-1010 USA
^b Greenhouse and Processing Crops Research Centre, Agriculture and Agri-Food Canada, Harrow, ON Canada N0R 1G0

View larger version (27K): [in a new window]   Fig. 1 Schematic of the – TDR probe

View larger version (23K): [in a new window]   Fig. 2 Examples of TDR waveforms from Probe 1 in a clay loam soil with different matric potentials. Apparent probe lengths for the gypsum and the soil are represented by La,g and La,s, respectively

View larger version (23K): [in a new window]   Fig. 3 Calibration of the TDR-measured dielectric constant of the gypsum and the soil against matric potential for the – TDR probes. Bars indicate ± one standard deviation of measurement. For the gypsum, a calibration curve was established with r2 = 0.998 using fitted parameters, r = 3.158, s = 21.452, = 0.0207, n = 3.150, and m = 0.228

View larger version (23K): [in a new window]   Fig. 4 (A) Relationship between TDR-determined dielectric constant and gravimetrically-determined water content. The calibration curve was determined using only the data obtained by Probes 1 and 2. (B) Comparison of water characteristic curves for the clay loam determined by the – TDR probes with that determined by the conventional-pressure apparatus

View larger version (23K): [in a new window]   Fig. 5 Response time of the dielectric constant of the gypsum and the soil during (A) desorption from saturation to = -100 kPa followed by (B) water absorption