Evaluation of MPS-1 soil water potential sensor

Soil water matric potential sensors are essential for understanding agricultural and natural ecosystems. However, accurate sensors that can be used for a wide range of soil moisture conditions have yet to be developed. The MPS-1 sensor by Decagon Devices, Inc. was tested and calibrated in a laboratory setting using pressure plate and suction apparatuses. This study evaluated the general performance of the MPS-1 sensor by: (1) testing for a wide range of varying soil conditions, including temperature and hysteresis; (2) determining measurement range, sensitivity, consistency, accuracy, and variation among sensors; and (3) developing a laboratory calibration procedure prior to field installation. Sensitivity of the MPS-1 sensor was found to be a highly nonlinear function of soil matric potential. Sensor-to-sensor variations were large, but were partly removed using the presented one-point calibration. Variation among sensors is largely eliminated by using a sensor-specific calibration. The MPS-1 sensitivity to temperature was relatively small and inconsistent, and hysteresis effects were relatively minor. Individual sensor output readings were consistent in time, remaining almost constant over a measurement period of 1.5 years. By comparing calibrated MPS-1 sensors with tensiometers in the field, we conclude that measurement uncertainty is less than 10 kPa (or 0.1 bar) in the range from 10 to 60 kPa.