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PS-2163
012-10538C PASCO Soil Water Potential Probe
7
Experiment Suggestions
•
Measure soil moisture over time.
•
Evaluate soil moisture content for various species of plants to determine
the optimal level of soil moisture.
•
Examine soil moisture content in a greenhouse to determine the amount of
irrigation.
Specifications (PS-2163)
PASCO Soil Water Potential Probe (PS-2513)
Introduction
There are two basic parameters that describe the state of water in soil: one is
soil water content, or the amount of water per unit of soil, and the other is soil
water potential, or the energy state of the water in the soil. Water potential is
often preferred over water content because it shows how water will move in a
soil or from the soil to the plant. In an object comes into hydraulic contact with
soil, the water potential of the object will come into equilibrium with the soil
water potential.
The Soil Water Potential Probe uses a solid matric equilibration technique to
measure the water potential of the soil. The probe has a static matrix - a porous
ceramic disk - that is allowed to reach hydraulic equilibrium with the soil that is
being measured. The probe measures the dielectric permittivity of the ceramic
disk to determine its water potential and thereby the water potential of the soil.
Installing the Probe
Because it measures water potential, the probe needs good hydraulic contact
with the surrounding soil. The preferred method for installing the probe is to
take some native soil, wet it, and pack it in a ball around the entire probe,
making sure that the moist soil is in contact with all surfaces of the ceramic
disk. The probe and moist soil are then packed into the soil at the desired
depth.
After the probe is installed, the hole that was excavated to bury the probe
should be back-filled with care taken to re-pack the soil back to its native bulk
density. Leave at least 15 cm of cable beneath the soil. Do not bend the cable
in a tight radius as it leaves the probe. At least 10 cm of cable nearest the
probe should remain in a straight line.
Sensor Range
0 to 45% volumetric water content in soil
Accuracy
± 4%
Resolution
0.1%
Power
3 mA at 5 V DC
Operating Temperature
-40 to + 60 °C
Default Sample Rate
10 samples per second
In the engineering
community, “soil suction”
is used instead of soil
water potential. Soil
water potential is simply
the negative of soil
suction.
