Soil moisture sensors tell you when, how much to water

01/20/2012 01:13:00 PM
By Tom Burfield

Growers first experimented with drip irrigation in the 1940s, but with the advent in the 1960s of polyethylene plastics to make the drip tubes, the practice quickly became widespread.

Today, drip is an irrigation method of choice throughout the United States, especially for high-value crops.

The process continues to be refined as technology improves and as water conservation becomes an increasingly significant concern.

At the forefront of these refinements is Gilbert Miller, area vegetable specialist who heads the soil moisture monitor project at Clemson University.

Miller has come up with a system that uses moisture sensors to determine when and how much to water crops.

The sensors have copper bands that send radio waves through the soil at depths of 4, 8, 12, 16 and 20 inches. By monitoring the strength of the radio waves that come back to the transmitter, Miller can determine how much moisture is in the soil.

Signals typically are sent out every 15 minutes, but the timing can be adjusted. The signals are sent to a radio that, in turn, sends them to the Internet, allowing Miller to monitor moisture levels from anywhere he has access to a computer or even a smart phone.

Solar powered

The system is powered by solar panels and can be set up to automatically trigger irrigation. Or Miller can activate irrigation manually.

A computer screen has an icon for each electronic valve that indicates when the valve is open and supplying water to the field.

“The system bases the need for irrigation on what is in the soil,” he says.

Growers already have several models that measure inputs—like rain and irrigation— and outputs—like drainage and evaporation.

But then the grower must figure out theoretically what a plant needs.

“The sensors pretty much do all of that for us,” Miller says.

It’s just as important not to over-irrigate as it is to not under-irrigate, he says.

“We’re trying to apply only as much water as what the plant can take up,” he says. The irrigation is often in short bursts, five or six times a day, rather than inundating the plant once a day or so.

Miller’s goal is to keep the water saturation as close to field capacity as possible— to the point where the water level is stable, not moving, and the water is present for the plant to use as needed.

When 15 percent of the water is depleted, Miller triggers the system to refill the “bucket” not quite to field capacity.

Labor, water saver

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