August 6, 2010
The advantages of shallow subsurface drip irrigation are many, but it’s still used sparingly in the lower Southeast on traditional row crops.
RON SORENSEN, AGRONOMIST with the National Peanut Research Laboratory in Dawson, Ga., explains shallow subsurface drip irrigation during the recent C.M. Stripling Irrigation Research Park Field Day in southwest Georgia.
The advantages of subsurface drip irrigation include the potential for more precise managing of water near the roots of crops, minimizing losses due to evaporation, installing systems in fields with irregular shapes, allowing for spoon-feeding nutrients (especially important in locations where rainfall can leach significant nutrients), and zoning of irrigation areas based on limited water supplies and differing water needs of soils and crops, says Ron Sorensen, agronomist and soil scientist with the National Peanut Research Laboratory in Dawson, Ga.
Sorensen was one of the presenters at this year’s annual field day held at the Stripling Irrigation Research park.
In shallow subsurface drip irrigation, he explains, drip tubing is being placed in the soil at approximately 3 to 4 inches deep.
“Then, we go into a strip-till operation, and we get our yield information from there,” he says of the work at the Stripling Park in Camilla. “We leave the drip tube in the ground, anywhere from three to five years. Using strip-till along with a GPS system, we stay off the tape, and this allows us to leave our tape out there and improve our yields.”
In the last year of the trial, Sorensen says, peanuts are put into the crop rotation. “Prior to harvesting peanuts, we pull up the drip tape, harvest the peanuts, and then go back into a cotton/corn rotation for three to five years. Then, we go back into peanuts,” he says.
Essentially, the drip tape is being used like a nozzle on a pivot, says Sorensen. “After so many years, nozzles go bad, and you throw them away and put on a new nozzle. That’s what we’re doing here. The infrastructure is still available, and the mainline is still there, so all we’re really doing is exchanging tape.
“If you’ve got some rented land — maybe a 10 or 12-acre field — you can get some blue lay-flat hose, punch a little hole in it, hook up to it, and go right into the tape. The blue lay-flat, the hose and everything, if you do it on a per-acre basis, you’re probably looking at $250 to $300 per acre. And you have that in for five years, the cost goes down to about $40 to $50 per acre. It’s very economical,” he says.
Yields in the trial have shown an improvement, says Sorensen. “Of course, with dryland corn, in some years you get really good dryland corn and in other years you get nothing. We usually run about 180 to 200 bushels of corn per acre. With cotton, we’re up to 1,500 to 1,700 pounds per acre. And in peanuts, we’re running right around 4,800 pounds per acre over the six to eight years we’ve been using this system,” he says.
The most difficult part of the process, he adds, is pulling up the drip tape.
“There is not a machine available — commercially — to pull tape out of the ground. They have them in Israel, but they don’t have them here, so that’s one thing we’re working on. If you have a break in the tubing, they make couplings so you can hook them back together in case you do get a hole. Or you can do it the cheap way, and put in a piece of blank tubing in there with a couple of hose clamps.”
The system, says Sorensen, is very inexpensive to run, roughly about $7 to $8 per acre, depending on how many holes you have and how much you’re paying your labor to fix the holes. “It does get to a point to where there are so many holes you don’t want to do it anymore, and that’s when you run that last year of peanuts, pull out the tape, and start over.”
Typically, shallow subsurface drip irrigation has used about 25 percent less water than a center pivot system, he says. “And we get the same or comparable yields, depending on the year. In some years, the pivot does better, and in other years, we’ll do better with the subsurface drip. Overall, we usually get by with less water with the drip. It takes about 15 to 20 gallons per acre to use this tape, and that’s to put out an inch in 24 hours. So if you have a 30 to 45-gallon-per-minute well that’s sitting vacant on the edge of a field, you can cover three to four acres with that.”
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