Researcher comparing drip, pivot systems for efficiency

HALFWAY, Texas - Subsurface drip irrigation does not guarantee increased yields or more efficient water use compared to other irrigation systems, says Jim Bordovsky, Texas A&M University research scientist.

But, when growers design a drip irrigation system correctly and manage it properly, they can increase production significantly and improve water use efficiency, he says.

Bordovsky, who works out of the Texas A&M Agricultural Experiment Station at Halfway, says High Plains farmers face the harsh reality of a diminishing water supply.

“We’ve not had normal rainfalls in a long time,” he says. “We continue to draw water from the Ogallala Aquifer for a 2-million-acre cotton crop, and it is being depleted. Pumping capacity cannot meet the demands in most fields.”

Bordovsky says average rainfall for the High Plains runs about 18 inches per year, and most of that falls during the growing season. “But we’ve gone through drought situations in July and August for the last few years.”

Those in-season dry spells, he says, put even more stress on an overworked aquifer. “We may soon see changes in water policy,” he says.

Whatever changes may occur in water regulations, Bordovsky says growers must design irrigation systems that use available water as efficiently as possible.

“A well-designed and managed subsurface drip irrigation system is the best available option for efficient water use,” he says.

“A good drip design includes proper sizing and arrangement of filters, drip tape, valves and plumbing components. Installation of drip laterals in uniform, straight rows is critical for ease of management and proper operation over the long term.”

Currently, Texas High Plains farmers have an estimated 250,000 acres in drip irrigation. “We’re adding more than 20,000 acres a year,” Bordovsky says. “Growers have seen phenomenal yields from drip systems, some close to four bales per acre.”

But it takes more than a system change to boost yields.

“Farmers have to manage SDI systems carefully to achieve high yields and efficient water use,” he says.

Uniform crop germination has posed the biggest challenge for the past two years.

Bordovsky set up a test, using a simulated zero rainfall scenario with rainout shelters. “We irrigated the soil profile with 7 inches of water. In some years, we needed less. In some cases, germination was still a problem.”

Bordovsky says farmers also must provide adequate system maintenance. “We had trouble with emitters plugging up,” he says. “We discovered that manganese in the irrigation water was causing the problem. We tried several acid concentrates to clear the emitters and finally added hydrogen peroxide, and that cleared the system out.”

He recommends growers analyze the water source for manganese and other potential problems before installing a drip system.

Bordovsky says concentrating drip systems on part of a field, rather than across the entire acreage, may prove more efficient. “We’ve made higher gross cotton yields with drip by concentrating water and other resources on only a portion of the previously irrigated area,” he says.

He has also tried using a chisel plow parallel with the drip tape. “We wanted to improve soil structure and to aid seed germination. We saw no advantage with germination compared to non-treated plots but we did get a bump in yield.”

Bordovsky says drip irrigation can increase efficiency significantly, if the system is designed and managed properly.

He ‘s also working with variable rate technology on center pivot irrigation systems. “We’re trying to determine if planned redistribution of irrigation water in the field will improve overall water use efficiency,” he says.

Bordovsky is using a 133-acre pivot, designed to apply different rates of water to different parts of the field, based on soil conditions, slope, etc. He divides the acreage into management zones and adjusts water application for each of the zones. Electrical conductivity and GPS technology provide a basis for water application rates.

He also uses a yield monitor at harvest to determine production differences among the various management zones.

Bordovsky says early tests are inconclusive but he’s continuing the research.

“Farmers likely will have even less irrigation water in the future,” he says. “And we have to overcome shortages with new technology and long-term water conservation.”

e-mail: [email protected]

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