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MADRAS - After two years of field trials growing crops of seed onions and carrot seed, Oregon State University researchers are finding that drip irrigation may save water, energy and have decreased need for weeding and herbicides when compared to the same crops grown under traditional overhead sprinkler irrigation.

In one experiment, OSU's Central Oregon Agricultural Research Center researchers in Madras grew hybrid seed onions in the summers of 1999 and 2000. They established the onions under solid-set sprinkling. In the each of the two springs following planting, half the established seed onion crop was irrigated using tape-drip irrigation and the other half by overhead sprinklers.

Although there were no statistical differences in the incidence of neck rot, bacterial soft rot and scape blight disease between the drip versus overhead irrigated onions, there were trends toward decreased yield and increased soft rot in the onions watered by overhead sprinklers, explained Claudia Campbell, research assistant at COARC in Madras.

"By the end of the two years of trials, we saw more soft rot and decreased yields on sprinkler-irrigated onions than with drip irrigation," said Campbell.

In a second experiment, also during 1999 and 2000, OSU researchers planted seed carrots under both drip tape and overhead sprinklers. They noted a trend of about a 25 percent yield increase for drip-irrigated over sprinkler-irrigated plots. And they noted half the level of Xanthomonas (a bacterial disease) in drip plots than in the sprinkler-irrigated plots.

Though growing seed onions and carrots have measurable results for yield and disease, there are other less measurable benefits that seem obvious to Campbell.

"My gut feeling is that there are a lot more benefits from drip irrigation in this region than we can measure in these experiments," said Campbell. "There are the benefits of reduced water usage, lower power bills and a reduction of herbicide use."

In the seed onion experiments, the amount of water applied to the crop to maintain similar soil water potentials was 26 percent less under drip irrigation than overhead watered onions.

"Less water used means less electricity needed to pump the water," she said. "And with drip, the water is delivered more precisely, allowing fewer weeds to grow. Fertilizer can also be delivered more precisely."

A more constant soil moisture level provides several other advantages, she said.

"There's less chance of over-irrigation and associated nutrient leaching. And there's less plant stress between irrigation."

Growers that use drip irrigation also notice fewer weeds and apply less herbicide, she said.

"And it is easier to clean the seed in drip irrigated crops because you are more precisely watering the crop, not the open spaces where weeds can grow, contaminating your seed crop" added Campbell.

Drip irrigation is physically easier than overhead watering, she said.

"You can irrigate more acres in one shot," said Campbell. "And it is much easier to change watering areas. You don't have to move pipe. So in short water years, drip could really pay off."

The major drawback to drip is that it costs a lot to get started, explained Campbell.

"You need to invest some money in sand media filters," she said. "But it's a lifetime investment; you depreciate it out over the years."

"It also costs about $200 per acre for the drip tape per year plus the installation and take out. But it doesn't require a high pressure pump and uses less energy."

Drip irrigation is more common in the Columbia Basin and the Ontario area, where irrigation water is scarcer, she said.

Analysis is still under way on some of COARC's drip irrigation studies. Results and details of the two-year drip irrigation seed onion and carrot seed studies can be found in "Central Oregon Agricultural Research Center 2001 Annual Report," (SR 1039) published June 2002. The report is available at COARS in Madras or by writing Clint Jacks, Superintendent, COARC, 850 Dogwood Lane, Madras, OR 97741.