Soil moisture sensors focus of irrigation research

• Researchers at the Stripling Irrigation Park in Camilla, Ga., are exploring all facets of irrigation, including the use of soil moisture sensors and the radio telemetry required to transmit data back to farmers.

With drought years starting to outnumber the years of plentiful rainfall in the lower Southeast, irrigation has become more of a necessity than a luxury, prompting growers to seek more efficient ways of determining when to irrigate and how much to apply, such as using soil moisture sensors.

Researchers at the Stripling Irrigation Park in Camilla, Ga., are exploring all facets of irrigation, including the use of soil moisture sensors and the radio telemetry required to transmit data back to farmers, says Calvin Perry, superintendant of the park.

“Irrigation has grown significantly in Georgia in recent years,” says Perry. “We now have more than 13,000 center pivots in the state, with more than 1,000,000 acres irrigated. The ratio of groundwater to surface water irrigation sources is about 2:1.”

The concentration of center pivots is in southwest Georgia, he adds, with more than half of the center pivots in the state in the Lower Flint River Basin.

The primary questions asked in irrigation are, when do I irrigate, and how much do I apply? says Perry. “We feel like if irrigation is timed and scheduled better, it can be optimized. Potentially, we may be able to save irrigations towards the end of the season if soil moisture levels are where they need to be, and maybe we can save that cost of application.”

There are many different ways of scheduling irrigation, he says.

“First, you can do it the old-fashioned way by getting out into the field, kicking the soil, or looking at the leaves on the plants. Or, you can predict crop water use. You can run irrigation scheduling tools that make irrigation decisions based on soil moisture measurements.

Another option

“Another option is to actively track soil moisture status based on sensors placed in the field. This information can be relayed to you or gathered from the field,” says Perry.

Soils in the Southeast Coastal Plain region exhibit a lot of variability, he notes, and growers don’t have a single soil type in their fields. For this reason, efficient irrigation in these soils is best achieved using some sort of site-specific management and maybe even automation using sensors, he says.

“There are several ways to get soil moisture data from these probes. The easiest way is to employ some sort of telemetry. Farmers are very busy, and they don’t want to have to go out into each of their fields and read a soil moisture sensor if they don’t have to. There are a number of ways to get this data,” says Perry.

The sensors themselves fall into two primary categories, the Watermark soil moisture sensors and some of the newer capacitance-type soil moisture sensors, he says. “These new types are much more expensive, such as $30 for a single Watermark probe versus $1,500 for some of these elaborate probes that have sensors at multiple depths. You pay a price for convenience and for getting those multiple depths.”

A new product on the market is the SmartCrop sensor manufactured by Smartfield out of Lubbock, Texas, says Perry. With SmartCrop, the plant is the sensor. By combining plant biology and agronomic science, SmartCrop can indicate high stress levels, plant disease, crop health status, and plant water needs.

The SmartCrop technology is based on the USDA patent known as BIOTIC (Biologically Identified Optimal Temperature Interactive Console). The technology uses a temperature sensor to monitor the leaf canopy temperature of your crop to determine water stress.

This sensor, placed in the grower’s field, takes this reading and relays the information to the Smartfield base station.

“It predicts that if your crop spends so many minutes beyond the maximum temperature, it’s experiencing moisture stress. If you irrigate the crop, the temperature of the canopy is going to come down. They’ve developed algorithms for a number of crops. They were developed in the Lubbock area, a semi-arid climate, so we’re looking at it to see if it would work under our conditions.”

Versatile tool

The beauty of this particular sensor, he says, is that you can mount it on a post and keep it about 14 inches above your canopy, or you can mount it sideways if you’re growing corn.

The next step, says Perry, is getting the data from a sensor that is placed in a field. “You can do this by radio. You can go with spread-spectrum license-free radio, and there are licensed radios like Mesh Networks, and there’s the Internet.

“A number of counties are putting in WiFi or WiMax across counties forming a wireless network. In this case, you’d have the ability to use WiFi sensors. But the tried and true method is to have a cellular signal, and this is mostly what we have across our region, either with the GSM with T-Mobile and AT&T, or CDMA with Verizon/Sprint. That is how we get most of our data.”

Decagon also has come up with an inexpensive way to get data via satellite, he says.

“Radio telemetry is basically getting that data from a spot in the field out to your pickup at the edge of the field. This way, you don’t have to walk into your field with a laptop computer, hook it up to a box, and download the data. You can receive continuous data. Or, you could have a radio near the sensors in the field, maybe put it up a little higher, and you could transmit that back to an office base.”

At the irrigation park in southwest Georgia, researchers are working on a Mesh Network, placing inexpensive sensors out in the field, says Perry. They inter-communicate with one another and then back to a base station at the edge of the field or a center pivot point.

“The bottom line in using all of this is to make a better informed irrigation decision,” says Perry. “It helps you answer the questions of when to irrigate and how much to irrigate. If you watch the soil moisture sensor data, you can see the decrease in the soil moisture status. That’ll give you an idea of how quickly it has dropped and give you an idea of how soon you need to irrigate.

“To know how much to apply, watch the data, and see if the soil moisture is increasing down to the depths of your crop roots at that particular time.”