Low-pressure system offers economical buried drip irrigation alternative



By Vicky Boyd

Editor



A new drip irrigation system that uses lower water pressure than conventional buried drip could provide growers an economical, energy-saving alternative to furrow irrigation.



Even in regions where water still is relatively inexpensive, the low-pressure drip system helps boost irrigation efficiency and increase yields, says Danny Sosebee, southwest area sales manager for Netafim USA in Edinburg, Texas.



R.L. Driebelbis, an onion and melon grower with Rio Queen Citrus in Mission, Texas, says the Low Pressure System is attractive because of its energy-saving potential.



“The technology is very, very new,” he says. “But it has tremendous potential. Right now, it’s showing significant benefits.”



A low-tech option

Netafim developed the LPS as a simple, economical way to introduce flood irrigators worldwide to the advantages of drip irrigation, Sosebee says. A water tank erected 6 feet above the ground has enough head to feed the system, which operates on 2 to 4 pounds per square inch of pressure. That compares with a conventional buried drip system that requires 12 to 15 psi.

In the United States, the system is suited to fields with canals or low-production wells that typically have low head pressure.



LPS also enables growers to irrigate larger amounts of land in one irrigation set, Sosebee says, citing a south Texas onion producer as an example.



With regular drip, the grower pumped 40 gallons per minute and could only irrigate 16 to 18 acres per set. With LPS, he irrigated 60 acres at a time, and the cycle between sets was much shorter.



“He got a much better stand on his onions, and his energy costs were 30 percent lower than flood irrigation,” Sosebee says.



The wetting and drying cycle is crucial in onions, especially during the 30-day germination period. Ideally, the field should be kept at the optimum moisture level throughout germination to ensure a uniform stand and maximum yields, Sosebee says.



Because LPS applies less water per hour, growers may have to adjust their management, Sosebee says. A typical emitter on a conventional system may apply 0.4 gallons per hour at 15 psi, compared with 0.1 gallons per hour at 2 psi on an LPS system. During hot days when the evapotranspiration rate is high, growers may have to run the system longer to meet plant water requirements.



Another irrigation tool


For the past three years, Netafim has tested LPS in the United States with several crops, including vegetables, row crops, nursery stock, cotton and rice.



The system isn’t designed to replace conventional buried drip, Sosebee says. Instead, it provides an economical alternative to growers who want to move from furrow to drip or learn more about drip technology without large up-front costs.



The system also may be an option for growers who lease land and don’t want to make a large investment since they’ll only be growing a crop there for a few years, Sosebee says.



A typical LPS costs about half the price of conventional buried drip, which currently ranges between $1,000 to $1,400 per acre. The expected life of an LPS system is five to seven years, but it is configured based on the farmers needs.



LPS consists of a collapsible layflat pipe ranging from 6 to 12 inches in diameter. Specially designed drip irrigation tubing that is typically buried 2 to 3 inches below the soil surface is attached to the pipe with fittings. The tubing either runs down either the furrow or the middle of the bed, depending on the crop.



Sosebee recommends installing a filter between the water source and system to remove soil particles and other matter that could clog drip emitters. Grower also can install a fertilizer-injection system to chemigate the field.



Depending on the elevation of the water source, growers may need to install a small lift pump to generate 6 to 7 feet of head pressure, Sosebee says.

Energy savings attracts interest

Driebelbis planted several hundred acres of Texas 1015 sweet onions on LPS in October 2005. But not every one of his fields was suited to the system.

Fields served solely by piped water with low sediments went into conventional drip. Other fields served by furrow irrigation favored the low-pressure system.

“I could use the drip tape to establish my plant populations and then chemigate,” Driebelbis says. “If the situation justified it, I could convert back to furrow water and subsidize the drip with furrow. The multiple options are more attractive to me.”

The onion quality at harvest was excellent, with yields of the most desirable size–jumbos–being about the same as buried drip fields, he says.

Driebelbis also is experimenting with LPS for honeydew melons, but he says the system will require modification. Melons typically are grown on buried drip shanked several inches below the soil, and high pressure is needed to open the tape. The original LPS relied on low pressure of less than 5 psi.

Netafim has developed a new layflat that can be pressurized up to 11.5 psi, which is enough to open most drip lines buried up to 10 inches deep.

One question Driebelbis says only time will answer is the durability of the portable manifolds.

“After I complete a 180-day crop, the system has to be portable, the manifold retrieved, rewarehoused and reinstalled,” he says. “I don’t have enough experience to know how durable it is after this amount of handling.”

Improved water-use efficiency

Daniel Leskovar, a plant physiologist at the Texas Agricultural Experiment Station in Uvalde, has experimented with LPS for two seasons, and he says the system shows promise.

His spinach trial involved applying 3.4 inches drip irrigation initially at planting to all of the LPS plots to help the seeds germinate and aid stand establishment.

He then applied three irrigations based on crop evapotranspiration—50 percent, 75 percent or 100 percent. In addition, Leskovar included seeding rates ranging from 265,000 to 530,000 per acre.



He compared those treatments to similar ones under center-pivot irrigation. The only difference was the center-pivot plots receive 1.9 inches of irrigation initially at planting.

Although south Texas growers typically cut spinach two to three times, Leskovar says he only harvested once because of the lateness of the test crop. Nevertheless, he says preliminary results are encouraging.

“The water-use efficiency—the amount of vegetation per unit of water applied—was close for the two systems except that it was higher for the low-pressure system at the 50 percent rate,” Leskovar says.

He attributes part of that response in the LPS to the drip system’s uniform water application rate to the root zone.

“The LPS system applies the water under the plant canopy, specifically at 2 to 3 inches deep, so evaporation loses may be less than with the center pivot,” Leskovar says. “This year we had two frosts, and we also noticed significantly less leaf damage in the LPS field than under the center pivot.”

Although the results of the spinach trial look promising, Leskovar says he wants to repeat it to see if he sees similar trends. He currently is comparing LPS and center-pivot using Texas 1015 sweet onions at varying seeding rates and irrigation rates.