Soil Moisture Sensing One Water-Saving Sensor Too Many?

This article was adapted from a University of Florida Institute of Food and Agricultural Sciences blog including a dialogue between water-use expert Michael Dukes, PhD, PE, CID, University of Florida professor, and Michael Gutierrez, UF/IFAS water resources technician, about a problem with multiple sensor installations in Florida. Gutierrez hosted the discussion about the “two sensors” situation in hopes that the industry could better understand the installers’ intentions and what went wrong.

During the summer of 2016, an area utility came to the University of Florida’s Institute of Food and Agricultural Sciences extension with a technology problem. Due to an incentive-based program, soil moisture sensors were being installed on new housing development irrigation systems. This is exactly the kind of best practice the irrigation industry loves to hear about.

In this instance, however, the installers elected to add rain sensors as well, which caused wiring issues.

The scenario led to discussions about what went wrong during the installation, as well as what — and how many — water-saving sensors are best for installation.

Rain Sensors vs. Soil Moisture Sensors

According to University of Florida Professor Michael Dukes, PhD, PE, CID, soil moisture sensors are more effective than rain sensors. “They’ll reduce irrigation two to three times more under the same conditions. And, longevity is better in soil moisture sensors,” Dukes said. To those familiar with research about these sensors, it makes sense to only use a soil moisture sensor.

However, because rain sensors have been around for a long time, they tend to be more readily used by contractors, practitioners and utilities.

A soil moisture sensor properly installed in an undisturbed soil profile

Dukes says that one of the things at the forefront of a practitioner’s mind is not wanting to see an irrigation system running when it’s raining. A rain sensor would solve that issue, and they assume adding a soil moisture sensor would make their results even better.

Two vs. One

Being in a profession that specializes in encouraging best practices, UF/IFAS Water Resources Technician Michael Gutierrez likes seeing practitioners install water-saving devices. In reality, Gutierrez realizes that having one well-installed, functioning device on a system is a rare thing, and he questioned the purpose behind installing two devices.

In the new housing development scenario, the reason rain sensors were added was to get the instant shut-off they would provide during a rainfall event.

According to Dukes, “We only have a limited amount of research on testing a soil moisture sensor with a rain sensor together, and in that limited study there was a benefit. It wasn’t a great deal, but there was a benefit.”

Dukes encouraged practitioners to think about the conditions where a benefit is gained. For example, to benefit from installing a rain sensor there has to be irrigation during a rain event. If there

A rain sensor properly installed

Photo credit: Michael Gutierrez, UF/IFAS ABE 18 Irrigation TODAY | January 2017

Photo credit: Michael Gutierrez, UF/IFAS ABE

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