Looking for the next big thing in irrigation? It's precision-applied water and plant nutrients in fields, even in high tunnels.
With irrigation's rising costs and advancement of precision agriculture technologies, variable-rate irrigation is primed for take-off. "We’ve been working on these technologies for years," says George Vellidis, head of University of Georgia's Vellidis Research Group.
"We’re at the point to where we can manage the data pretty well . . . to measure crop response and do variable-rate applications of fertilizers, plant growth regulators, defoliants and other inputs."
Now, he contends, it's time to more efficiently manage water.
It starts with yield maps that show changes in yields resulting from various water patterns in a single field. Bright green circles within a field, for example, can pinpoint leaks in a center pivot. You can see where it would be economically beneficial to irrigate at the higher rate.
There’s no reason to water non-crop areas. And, based on soil type and yield potential, there's no reason to overwater or underwater with VRI.
"It’s something we need to start doing," stresses the agronomist. "It’s economically feasible."
The technology allows you to change the rate of water application throughout a field according to need.
“If you want to choose an application rate that’s 50% of normal, then you cycle the [nozzles] on and off – 30 seconds on and 30 seconds off," he explains. "You can make things more complicated by including the speed of the pivot in the equation.”
Stepping-up to VRI
Many commercial center pivot manufacturers now offer VRI systems that work with their panels. There are also systems that can be retro-fitted onto pivots from different manufacturers.
The most expensive phase of retro-fitting VRI to a pivot is the first span, Vellidis says. As you add spans, the cost drops. A 75-acre pivot would cost about $16,000, according to one company offering VRI retro-fitting.
But as he points out, the ‘on-off’ option doesn't address agronomic VRI – varying water rates according to plant needs based on yield map data. That's where economic benefits of water-use efficiency can be maximized.
VRI allows changing the rate over crop areas to meet the crop demands. One south Georgia grower, for example, created irrigation management zones, each with a unique application rate and realized water savings rate of about 7½% over his normal application rates. He also had more uniform yields and higher yields overall.
“Learning how to create irrigation management zones and is very important in today’s environment, not only for irrigation but for all types of variable-rate applications,” says Vellidis.
Going the dynamic step
The next step is a dynamic VRI – responding to whatever the crops are telling us in each of these irrigation management zones. With dynamic VRI, soil moisture sensors tell you the soil moisture conditions in the individual zones.
“Then we try to put on the amount of water the soil moisture sensors tell us to put on," he explains. "It might be one inch today, and it might be ¾-inch next week.”
Soil moisture sensors designed to work specifically with VRI systems also are available to farmer. UGA's Smart Sensor Array, he explains, is a low-cost wireless soil moisture sensing system. “This type of information is necessary to make good irrigation scheduling decisions – especially if a variable-rate irrigation system is used."
A smart sensor node is a combination of electronics and sensors installed at each field location. UGA's SSA node consists of a circuit board, a radio frequency transmitter, soil moisture sensors and temperature sensors. Each sensor node accommodates up to three Watermark soil moisture sensors and two thermocouples for measuring temperature.
– Hollis is editor of sister publication Southeast Farm Press