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A New Resistance Sensor for Monitoring Soil Matric Potential

State Experimental Station of Agro-Ecosystem in Fengqiu; State Key Lab. of Soil and Sustainable Agriculture Inst. of Soil Science, Chinese Academy of Sciences, Nanjing 210008, People's Republic of China

View larger version (31K): [in this window] [in a new window]   Fig. 1. Schematic of the prototype resistance sensor. All measurements are in millimeters.

View larger version (21K): [in this window] [in a new window]   Fig. 2. Effect of polyacrylamide (PAM) on reproducibility of resistance measurements with the same sensor: (a) with PAM, (b) without PAM. Arrows indicate sequence of measurements (drying); the sensor was installed in the soil sample and water was removed by air drying.

View larger version (14K): [in this window] [in a new window]   Fig. 3. Measured resistance as a function of soil temperature for two sensors. Each data point represents an average of two measurements. RT/R25 is the ratio of the measured resistance at a temperature T (°C) and 25°C.

View larger version (13K): [in this window] [in a new window]   Fig. 4. Measured resistance as a function of electrical conductivity for three sensors.

View larger version (11K): [in this window] [in a new window]   Fig. 5. Calibration function between electrical resistance (R) and soil matric potential ().

View larger version (17K): [in this window] [in a new window]   Fig. 6. Comparison of soil matric potentials measured with resistance sensors vs. tensiometers in the sandy soil. The first wetting–drying cycle was used for sensor calibration and the subsequent cycles for sensor validation.

View larger version (19K): [in this window] [in a new window]   Fig. 7. Soil matric potential determined by resistance sensors and tensiometers in two different soils. The sand was used for calibration and the silty clay soil was used for validation.

View larger version (15K): [in this window] [in a new window]   Fig. 8. Response time of three electrical sensors during water desorption from saturation to a matric potential of –10 kPa.