Soil Moisture Gauge

Frequently Asked Questions about the AQUAFLEX Soil Moisture Gauge

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What is AQUAFLEX?

AQUAFLEX is a system for gauging soil moisture and temperature.

The AQUAFLEX soil moisture gauge features a long flexible sensor that measures the average soil moisture along its length and the soil temperature near one the end of the sensor.

An AQUAFLEX soil moisture gauge is buried in the soil and can be connected to a number of devices including:

  • The AQUAFLEX Handheld Reader
  • Third Party irrigation controllers, dataloggers etc

The AQUAFLEX Logging Sensor has its own built in datalogger so it is completely self-contained.

How Long is The Sensor?

The AQUAFLEX soil moisture gauge sensor is a thin strap about 10 feet (3 meters) long and an inch wide.

Because AQUAFLEX has a long sensor and uses a relatively large sample size (6 litres), AQUAFLEX "Spatially Averages" localised moisture values resulting in reliable and repeatable results.

Why is Spatial Averaging Important?

One of the biggest problems with most soil moisture gauges or monitoring devices is that they measure moisture in a very localized area. This is a problem because soil moisture is not uniform.

Many factors affect the uniformity of soil moisture, including the uniformity of irrigation and rainfall, crop root distribution, microclimate and soil properties.

Averaging soil moisture measurement across a broader area provides a better indication of general trends in local soil moisture.

How Do You Use The Aquaflex System?

First, you bury one or more soil moisture gauges or sensors in the soil. (Eg; horizontal in a root zone, curved around a tree root, or at an inclined angle to measure full rootzone depth).

You then download the data from the logger using a Palm handheld computer or Laptop PC.

Then you use the AQUAFLEX software to create graphs of soil moisture and temperature. The information on the graphs can be used to determine when and how long to irrigate. Target moisture set points (full and refill points) can also be added to the graphs.

Unlike traditional probes, AQUAFLEX takes the average soil moisture and temperature measurement over a 3m sensor. The AQUAFLEX sensor is very flexible allowing it to be placed in almost any position eg in an 'S' shape, 'U' shape, straight, curved, spiral etc.

Why is Continuous Monitoring Important?

In most soils and growing conditions, soil moisture and temperature vary dramatically, often over quite short periods of time. Continuous monitoring provides the full picture that shows just how widely and quickly these changes are taking place.

Continuous monitoring also removes the worries of missing key readings. You simply collect the information when it is convenient for you - without missing anything important that has occurred.

How Does AQUAFLEX Measure Soil Moisture?

AQUAFLEX uses a unique technology to measure the dielectric constant of the soil. Since the soil dielectric is a moisture-dependent property, these measurements can be converted to accurate measurements of volumetric soil moisture (the amount of water in a given volume of soil).

AQUAFLEX uses signal processes which are similar - but superior - to time-domain reflectrometry (TDR).

Special processes have been developed that allow TDR-like measurements over a longer conductor and improve the correction of these values for soil temperature and salinity.

How Accurate is the AQUAFLEX Soil Moisture Gauge?

For agricultural soils measurements are normally accurate within two percent volumetric moisture, with a measurement repeatability of about 0.25 percent volumetric moisture, using standard calibrations. Soil specific local calibrations are easily made using the built in feature in the Aquaflex software.

Soil temperature measurements are accurate to within 0.9 degrees Fahrenheit (0.5 degrees Celsius).

What is the Moisture Range of the Sensor?

AQUAFLEX precisely measures soil moisture levels from dry to saturation.

How Do You Install The Sensors?

You simply dig a trench large enough for the Aquaflex soil moisture meter, placing the soil on a polythene sheet or similar in the same order that it was removed in. Place the Aquaflex sensor on its edge at the desired depth and replace the soil in the same order that it was removedand as near as possible to the same density of the undisturbed soil.

Any stones that were removed should be replaced into the trench, although care needs to be taken not to place them directly on or beside the sensor.

For specific instructions and guidance please contact us at Aquaflex as correct installation is crucial to gaining informative and representative data.

How Do You Get Data Out of the Logging Sensor?

Data can be retrieved from the AQUAFLEX Logging Sensor in two different ways:

  • Direct connection to a laptop computer.
  • Connection to a Palm handheld computer. Data is then conveniently transferred from the Palm handheld to a laptop or desktop computer.

Remote data retreival by telemetry is also possible.

How Big is the Logging Sensor?

The dimensions of the AQUAFLEX Logging Sensor (battery box dimensions):

6 inches wide, 7 inches high and 4 inches deep.

The Battery box weighs about 2 pounds when loaded with batteries.

How is AQUAFLEX Powered?

AQUAFLEX is a stand-alone, self-powered system. This power is provided by alkaline batteries.

How Long Can the Logging Sensor Store Data?

The Logging Sensor is equipped with wrap-around memory, where the newest readings overwrite the oldest readings.

The data capacity depends on the frequency of measurements (sampling interval). The AQUAFLEX Logging Sensor can store nearly two months of data when taking a reading every hour.

What Does AQUAFLEX Cost?

Total system prices depend on cable lengths, number of sensors etc. A detailed quotation is available on request.

How Does the AQUAFLEX Sensor Compensate for Temperature?

The sensor electronics (buried under the ground with the sensor cable) includes a device which measures the soil temperature. This temperature measurement is used to compensate the moisture measurement for differences in both the electronics and the soil itself at different temperatures.

How Does the AQUAFLEX Sensor Compensate for Soil Conductivity?

AQUAFLEX determines moisture by measuring the time taken for a pulse to travel along its sensor cable.

It is well established (and backed up by our own careful measurements) that increasing the conductivity of the soil has two independent effects:

  • Firstly, it will alter the speed of the pulse along the sensor cable (this in itself will introduce an error into the moisture measurement).
  • Also, the shape of the returned pulse will be altered in a known fashion.

The AQUAFLEX sensor makes a measurement of the shape of the returned pulse and uses this to compensate the moisture measurement against errors caused by changes in soil conductivity.


If any of your questions about the Aquaflex soil moisture gauge system are not answered here, please contact us.

"The Aquaflex soil moisture gauge from Streat Instruments."


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