Use of Radio Telemetry and Capacitance Probes to Monitor Soil Moisture

Utilizing capacitance probes (C-Probes) in conjunction with radio telemetry, soil moisture was monitored in a cotton field and an alfalfa field in Maricopa, Arizona. Once installed, the data collected by the C-Probes were interrogated every 15 minutes and automatically downloaded by a base station located at a site nearby. The base station, which was connected to a desktop computer, could then be activated to download the data into the computer where the data could be viewed. In addition to the C-Probe data, neutron moisture probe access tubes were also installed at the sites and soil moisture readings taken. The data were compared over several months. When comparing discrete soil moisture values, i.e., values at a particular depth, the C-Probes were not in agreement with the neutron probe readings. However, when comparing soil moisture over a meter depth, or comparing water use data, the C-Probe and neutron probe data compared well. The theory behind this discrepancy is that the C-Probe only measured a discrete soil volume whereas the neutron probe samples a much larger volume. At any particular depth, the comparison may be poor because the two instruments are measuring two separate soil regions. However, when comparing a larger soil volume, the two measurements were in agreement.