A major disadvantage of subsurface drip irrigation, says east Alabama farmer Mitchell Lazenby, is that it's by necessity a trial-and-error venture, primarily because no one else in the region has been doing it for very long.
“No one around here has been doing it for 15 to 20 years, so you can't go to another farmer and ask questions about the right and the wrong way to do certain things,” says Lazenby, who installed a subsurface drip irrigation project last year in one of his cotton fields.
Lazenby, who farms in Lee County, buried the irrigation tape from eight to 15 inches deep. “The biggest reason we went down 15 inches was to give us some flexibility if we ever decide to do a different type of tillage. In other places, we felt the tape shouldn't be buried so deep,” he says.
The drip tape, explains Lazenby, is placed between every other middle. Emitters are located every two feet along the row. They put out about three tenths of a gallon per hour per emitter.
The first year of the subsurface drip experiment was encouraging, he says. “In 2001, we came in and picked about a bale and a half per acre on the first go-around. Then, we picked a little over a bale on the second trip. We don't expect the same results this year. We put in a new filtration system and had some down time in July when we lost a pump. So things don't look as good as they could have been,” he says.
Lazenby is pumping water from a lake — about 1,500 feet from the source to the field. In principal, subsurface drip irrigation does a very good job, he says. But problems can arise.
Crop rotation is a big question mark with using subsurface drip irrigation, says Lazenby. “If we come back with a different crop, we don't know if we want to stay directly on top of the old row. If we get off that row, we're not sure how that'll affect us if we want to grow vegetables or other hand crops for which you use disposable tape on the surface of the ground.”
So far, the system has worked well for Lazenby's cotton crop. “Our planters are equipped with row cleaners. So we can go in, burn down the cover, and brush the old stubble out of the way. Unless we change up our rows, we know we'll be in line with where the tape is buried.”
Subsurface drip irrigation is a new approach to irrigating row crops in Alabama — new to farmers and researchers alike, says Larry Curtis, Auburn University Extension engineer.
“We've been conducting research at the experiment station in north Alabama's Tennessee Valley for about six years. And we'll be harvesting our third crop this year at south Alabama's Headland experiment station,” says Curtis.
Growers should be prepared for a large-scale undertaking when installing subsurface drip irrigation, he says. “Installation is a big and difficult job, and it must be done correctly. Damage can occur during installation, and precautions must be taken to prevent this from occurring. Proper installation is very critical to the success of subsurface drip irrigation,” says Curtis.
Materials for such a system can run in the $500-per-acre range, he continues. “After adding in labor costs, you're in the $750-per-acre or better range by the time you've installed the system, not counting any water resource development costs.”
Another important factor in subsurface drip irrigation is keeping the lines flushed, notes Curtis. “You have to chlorinate the system, and you may have to acid-treat it. But there are farmers in Texas and Arizona who have been using this type of irrigation for 15 years. If things are done correctly on a timely basis, you can keep these systems open and running.”
Research planned for north Alabama will look at using a guidance system along with drip irrigation, he says. “By putting information about the location of the drip system in the guidance system on the planter, we can plant exactly where we want in relation to the drip.
“This is where we need to be headed with this type of irrigation. We need to install the drip tape with the guidance system so we'll know exactly where the tape is located. Once the information is in the system, it'll help us in future plantings.”
Research being conducted in Headland is looking at subsurface drip irrigation in a cotton-peanut-cotton rotation with drips under every row, between rows and in twin-row peanuts, says Curtis.
It's important, he says, that subsurface drip systems be planned to achieve uniformity in the field. Uniformity, he adds, depends upon factors such as correct pipe sizes and runner lengths.
“The products we currently use must be installed on relatively flat ground or uniform to sloping land. We plan to install some in north Alabama that will operate on rolling terrain. This is something I've been pushing manufacturers towards for some time. We need this type of product for many of our locations in Alabama.”
Yields have been very good in subsurface drip trials in the Tennessee Valley, notes Curtis. “In the five to six years of the experiment at Belle Mina, we've harvested cotton in the two to three-bale range. Average yields over all the trials have been 2.25 to 2.5 bales per acre.”
There currently are two farm-scale subsurface drip installations in Alabama, he says. One is at the Tate farm in north Alabama while the other is at the Minter farm in the central part of the state, near Selma.
“These farms are in their second year of using these systems. Yields were good last year, but we're still on a learning curve with this method of irrigation. There's still a lot we don't know. These farmers are applying fertilizer and other materials through their systems, and they're doing it successfully.”
It's important, however, that growers don't “plug up” these systems with other materials, says Curtis. “Some of these fertilizers contain clay-based materials. If you put those in the system, you can close it up and destroy it if you're not careful.”
In north Alabama field trials, subsurface drip systems were used to put out six gallons, 4.5 gallons, three gallons and one gallon per minute per acre, says Curtis. The mid-range — 4.5 gallons per minute per acre — did as well as six gallons, he says.
Total water use from subsurface drip irrigation has proven to be “at least comparable” to sprinkler irrigation systems, he says. “I'm not sure we can't conserve more water with these systems, but we're not seeing that at this time. There are innumerable ways we could look at it. For example, we could run the system every third day, putting out one inch. But we haven't tried that.”
Horsepower requirements for subsurface drip irrigation depends upon the location of your water source, says Curtis. “There are potential savings in the area of horsepower because these systems operate at lower pressures. I'd say one half to three quarters horsepower per acre is a good rule of thumb if you have a typical lift and a typical pumping distance.
“If you have an extremely high lift and you're coming out of a very deep well where the pump is set deep, horsepower requirements would be higher.”
Subsurface drip systems can be a good fit for small fields, says Curtis. “If you're in an area where you can use a relatively small well, you could use that well hooked directly to a system to irrigate small fields. You possibly could use a 7.5 horsepower single-phase pump to irrigate 20 acres. If you can get 80 gallons per minute out of a four-inch well — with a 7.5 horsepower pump — that would irrigate some of our smaller cotton fields in Alabama.”