Soil Moisture Monitoring Using a Portable Capacitance Probe

by Ronald Phillips,
Mike Dishman,

Document Type: Proceeding Paper

Part of: Management of Irrigation and Drainage Systems: Integrated Perspectives


Accurate monitoring of soil moisture has long been in integral part of a successful agricultural management system. Water has increasingly become a valuable and much sought after natural resource as its supply dwindles and demands for its use escalates. For more than thirty years the neutron probe has been used to measure soil moisture and aid the user in water management. In recent years there have been attempts to find alternative systems which compare favorable to the neutron probe's accuracy, precision and acceptance by the research community. The manufacturers of the Sentry 200-AP capacitance probe sought to emulate the field use of the neutron probe as well as the neutron probe's reputation as an accepted monitoring tool. The capacitance probe responds to the dielectric constant of the soil medium and converts this measurement to a direct volumetric water content. Similar in application to the neutron probe, the Sentry 200-AP is currently being evaluated across the country by university and governmental researchers. The advantages and disadvantages of the probe have been documented by these researchers based on their data and experience with the probe. Those studies will be reported here as well as findings from the manufacturer of the probe. Results from the July 1992 ASCE meeting in Logan, Utah will be discussed, as well as discussion on similarities and differences between the Sentry 200-AP and other measurement technologies. A large number of shallow evaporation basins are currently being used to dispose of subsurface agricultural drain water in the southern San Joaquin Valley of California. The proliferation of evaporation ponds has led to an increase in shallow, saline aquatic habitats in the arid region of California. The biological characteristics of evaporation ponds is discussed as a first step in identifying factors that play an important role in determining the potential for contamination to waterfowl, shorebirds, and other wildlife resulting from food chain bioaccumulation of toxic constituents present in these ponds. All ponds have macroinvertebrate and planktonic assemblages of low diversity with a negative correlation between taxonomic diversity and salinity.

Subject Headings: Probe instruments | Soil water | Ponds | Evaporation | Systems management | Subsurface drainage | Salinity | United States | California | Utah

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