Farmers and UC test drip irrigation in alfalfa fields

In a field outside Chowchilla, farm manager Seth Rossow is finding that a buried drip irrigation system lets him grow a higher-quality alfalfa crop because the system gives him greater control over the amount of water he delivers to the plants.

At the University of California, Davis, agronomy test fields, researchers planted their first-ever plot of alfalfa under drip irrigation last October, in order to conduct a side-by-side comparison of water use, yield and crop quality under buried drip and check irrigation.

The chronic threat of water shortages has spawned new interest among farmers and researchers alike in learning if buried drip irrigation can be used to deliver water to alfalfa more efficiently.

It is already becoming clear to researchers that buried drip irrigation in alfalfa has benefits, as the system has been used to produce higher yields of a higher-quality crop. But the system also brings challenges, like building a large enough root structure or leaching salts out of the root zone.

At Bert Wilgenburg Farms, Rossow manages alfalfa with drip irrigation lines buried 14 inches below the surface and gypsum watermark sensors to accurately gauge how much water the crop needs.

While he is still tinkering with details of the buried drip system, Rossow said he is already enjoying the control it gives him over the amount of water applied to the crop.

"One of the things I like is that I have better control. If I want to apply just an inch of water, I can," he said.

A main reason for installing buried drip at the Chowchilla alfalfa field was water efficiency. But sometimes the improved control that comes with drip irrigation can translate into better crop quality as well as better water efficiency.

"One of the things we wanted was a little less lignon and a little more protein and TDN(total digestible nutrients). We got about 1 percent more protein and 1 percent more TDN. I'm noticing the stands last a lot longer. There are more crowns per square foot and the stems are finer," Rossow said.

He discussed his experience as farmers looked at the test plots on the Davis campus during the annual UC Alfalfa and Biofuels Field Day.

There are challenges with buried drip systems, and one of them is finding a way to prevent gophers from chewing holes in the drip lines.

"Gophers are probably one of the biggest impediments to buried drip in alfalfa," said Dan Putnam, UC Cooperative Extension forage specialist who is supervising the campus drip trial.

The key to answering the gopher issue may be burying the drip lines deep enough that the gophers don't get at them.

"We buried it at 14 inches, and I wouldn't go much closer to the surface than that because of the gophers," Rossow said.

An unexpected challenge in the drip irrigation experiment is finding a way to help the plants build a substantial enough root system.

"The yields were similar to some of our established fields. You might do better by fluctuating the amount of water applied in an irrigation, because the alfalfa doesn't develop a huge root system under buried drip," Rossow said.

He has decided to fluctuate the moisture more on the buried drip in order to build a larger root structure, which should help to stimulate re-growth after cutting.

UCCE specialist Bob Hutmacher said that during a trial in the Imperial Valley in the 1990s, he also found it challenging to develop adequate root structure in alfalfa grown on drip.

"If the yield levels were really high, we ended up with deficiencies in potassium because the wet area was smaller," Hutmacher said.

In the Brawley drip irrigation alfalfa trial in the 1990s, the main payoff came through high yields.

"We were seeing about a 20 percent increase in efficiency. It wasn't from using less water, but from improvements in the yield," Hutmacher said.

An important part of the equation in installing a buried drip system, according to Hutmacher, is the soil type at the site.

"Anybody working with drip irrigation, regardless of the crop, needs to look at the soil conditions. When we worked with drip in the Brawley area, the soil was clay. Not clay-loam, but clay," he said.

He found that the drip lines had to be buried deep enough to prevent water coming up to the surface and creating problems for equipment.

"Root intrusion was not an issue in any of the trials we did in the Imperial Valley. But we started at 16 inches, and had water coming to the surface in some places. We took it out and put it back in at 26 inches. We had no gopher problems, and no water coming to the surface," Hutmacher said.

Weeds can be less of a problem in buried drip systems that are functioning well because weed seeds close to the surface do not receive irrigation water.

(Bob Johnson is a reporter in Magalia. He may be contacted at bjohn11135@aol.com.)