Water & Nutrient Management:
Soil Moisture-Based Irrigation Systems
Tensiometric Measurement:
Granular Matrix Sensors (GMS)
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Working Principle
The electrical resistance between electrodes embedded in a porous medium (block) is proportional to its water content, which is related to the soil water matric potential of the surrounding soil. Electrical resistance reduces as the soil, hence the block, dries.
Description
The sensor consists of electrodes embedded in a granular quartz material, surrounded by a synthetic membrane and a protective stainless steel mesh. Inside, gypsum is used to buffer against salinity effects. This kind of porous medium allows for measuring in wetter soil conditions and lasts longer than the gypsum blocks. However, even with good sensor-soil contact, GMS have re-wetting problems after they have been dried to very dry levels. This is because of the reduced ability of water films to re-enter the coarse medium of the GMS from a fine soil. The GMS material allows for measurements closer to saturation. Measurement range is 0.10-2.0 bar.
Advantages
- Reduces the problems inherent to gypsum blocks (i.e., loss of contact with the soil by dissolving, and inconsistent pore size distribution)
- Up to 4 inch measurement cylinder radius
- No maintenance needed
- Simple and inexpensive
- Salinity effects buffered up to 6 dS/m
- Suited to regulated-deficit irrigation
Drawbacks
- Low resolution, limited use in research
- Slow reaction time. It does not work well in sandy soils, where water drains more quickly than the instrument can equilibrate
- Not suitable for swelling soils
- If the soil becomes too dry, the sensor must be pulled out, re-saturated and installed again
- Temperature dependence. If connected to a logging system, another variable and sensor for temperature must be added to the system
This page was last updated on June 15, 2010.
Videos
- Welcome and Outline of Contents
- Timed Irrigation
- Bypass Timer Irrigation
- On-Demand Irrigation
- Irrigation Components
- Soil Moisture Sensors
- Irrigation Sensor Placement
- Application of the System
- Irrigation Sensor Families
- Neutron Probe
- Time Domain Reflectometry
- Capacitance Probe
- Combined Probe
- Frequency Domain Reflectometry (FDR)
- Amplitude Domain Reflectometry
- Phase Transmission
- Time Domain Transmission
- Tensiometer
- Gypsum Block
- Granular Matrix Sensors (GMS)
- Heat Dissipation
- Soil Psychrometer
