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Growers looking to squeak by fall irrigation

Even growers who are lucky enough to have well water reserves are casting a wary eye on the skies and wondering what spring 2008 will bring when it comes to water availability and/or cost. A lot depends on which and how it is irrigated.

“Almonds must be irrigated post-harvest to maintain fruiting spurs for next year,” says Blake Sanden, Kern County farm advisor. “By reducing evaporative losses, a double-line drip system on a soil that ‘subs’ well can save 6 inches to 8 inches compared to micro-sprinkler systems — even more for first- through third-leaf orchards.”

Pistachios don’t need a post-harvest irrigation, but it is essential to refill the profile during the winter in order to maintain good shoot and yield growth for the following year, according to Sanden. “For single line drip systems at 4 gph per tree on clay soils, a total of 8 to 18 total days of run time may be required, depending on the age and vigor of the trees.”

With a water crisis looming across the state, investing in more efficient irrigation systems could pay huge dividends in the future — even if the up front investment is significant.

“Micro-systems for grapes and trees, especially immature blocks, can save 0.5 foot to 1 foot of water, compared to flood,” Sanden says. “Table grape growers already on drip can't do much; they’re basically pumping water to fill berries. But, establishing a new vineyard with drip will save as much as 1.5 feet of water.”

For existing winegrape vineyards, there’s not much wiggle room left, according to Larry Williams, plant physiologist at UC’s Kearney Ag Center.

“Growers are already pushing the envelope on deficit irrigation, for the most part,” he says. “It’s fairly well established that we can irrigate at 80 percent of ET without reducing yields. In some cases, growers might be able to go a little lower than that — maybe down to 75 percent of ET.”

Next year’s irrigation management strategy will of course depend largely on what happens this winter.

“If we get enough winter moisture to fill the soil profile, growers can irrigate less and get away with it,” Williams says. “If there is one place where I feel growers might be able to save on irrigation, it’s the period between bud break and bloom. The vines only need about 12 percent of the season’s entire water requirements during that time, but growers tend to over-irrigate during that period.”

On the North Coast, growers are generally blessed with more dependable water supplies and cooler temperatures during the summer to relieve some of the pressure. But, water is still a major concern, which could get much more critical if adequate rainfall does not refill holding ponds, which were short this year.

“Growers are really thinking about irrigation,” says Nick Frey, president of the Sonoma County Winegrape Commission. “I think we’ll see a lot more post-harvest irrigation applied with drip rather than sprinklers.”

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