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Irrigating almonds with limited water supply

University of California irrigation specialist Dave Goldhamer sounds like the good cook who reminds us — “save room for dessert,” when he talks about how to irrigate almonds with limited water supplies.

About 300 growers — most who have far less water available this season than ever before — listened intently to Goldhamer as he detailed a variety of recipes to get growers through 2009, hopefully with a respectable crop. He spoke at a drought irrigation management workshop in Kerman, Calif., organized by UC Cooperative Extension Madera County Farm Advisor Brent Holtz.

However, Goldhamer emphasized to the crowd at Panoche Creek Packing that perhaps more important than getting through 2009 is surviving to farm again in 2010.

That will not happen if producers do not save at least 3 to 6 inches of water for the trees after harvest this season. If they don’t, yields can be dramatically reduced next year, regardless of the amount of water available during the growing season.

Almond trees planted in the San Joaquin Valley can be kept alive with as little as 8 inches of water, applied judiciously.

It can take up to 49 inches of water to produce a maximum crop in the San Joaquin Valley, where the majority of the state’s estimated 660,000 acres of producing orchards are planted.

Most SJV almond producers have access to a water supply this season somewhere between 8 and 49 inches.

How best to utilize what a grower has was the focus of Goldhamer’s presentation.

Pistachio trees can be stressed during a period within the growing season — mid-May to early July — without significant yield loss. However, almonds cannot tolerate stress without some impact.

Regulated deficit irrigation (RDI) can minimize the impact.

In a series of tests, Goldhamer said water was cut off in almond trees at weekly intervals from 53 days to 4 days before shaking.

Although nuts per tree (8,640 versus 9,530) and yields (1,384 pounds per acre versus 1,723 pounds per acre) were notably different for eight pre-harvest irrigation cutoff dates, in the world of science spreads between treatments were not “significantly different.” One reason for this is because water-stressed almonds compensate by increasing fruiting density.

However, kernel weight was different for pre-harvest water amounts ranging from just under 20 inches for a June 25 water cutoff to 31.5 inches for an Aug. 12 irrigation cutoff date.

Trees with a June 25 irrigation cutoff date were severely defoliated, but leaves came back with post harvest irrigation.

Conventional wisdom by researchers in the mid-1980s was that severe defoliation would greatly impact production the next year. It does not, said Goldhamer. He adds that the growers can even use partial defoliation as an indicator of an orchard’s level of stress. However, make sure there are leaves on trees after harvest for photosynthesis from a post harvest irrigation.

“Cutting edge” growers go to extremes to ensure the full benefits of post harvest irrigations to the point of irrigating pollenizer rows during nonpareil harvest.

“Some growers get nuts off the berms into the dry rows. To keep the nuts dry, they reduce the operating pressure of the drip or micro sprinkler system to reduce the wetting patter from say 10 feet to 5 feet,” Goldhamer explains.

He admits this is not very energy efficient, but it can be critical in the following year’s crop.

“Trees deprived to 12 inches of pre-harvest water reflected about a 300 pound per acre yield decline. When trees are denied post harvest water, the loss can be 800 or 900 pounds per acre the following year,” Goldhamer said.

Almonds are most sensitive to water stress in the post harvest period of mid-August to the end of September. This is when there is bud differentiation for the next season. Without sufficient water, flowers the following season will not evolve into fruit, he explains.

This stress period is the same for all cultivars and for all areas of the state.

Just 5 to 6 inches of water can result in yield differences of three to four times that of trees without post harvest irrigation.

“If I had only 18 inches of water available this year, I would save 9 to 10 inches for post harvest irrigation,” emphasizes Goldhamer.

In calculating regulated deficit irrigation, it is critical to match it with the orchard planting configuration.

Use real time CIMIS data to calculate tree water use in a drought situation. Historical water use data can be off as much as 20 percent in any given year.

The crop coefficient for calculating almond’s water use has been historically low. It was once thought to be 0.95. Goldhamer believes it is closer to 1.18.

If the water supply is limited, reduce the number of irrigations per season. If the water supply is only 75 percent of normal, apply available water in 28 irrigations rather than the full water supply of 30 irrigations. For a 50 percent water supply, reduce the irrigations from 28 to only 14.

When immature orchards reach 50 percent to 60 percent shade, it is considered a mature orchard for water needs, even though it is not a fully producing orchard.

Although almonds are high water users, they use water more efficiently than other crops. Goldhamer says almonds irrigated with 10 percent less water experience only an 8 percent yield loss. At 20 percent less water, yields decline 16 percent. With most crops it is a one-for-one relationship.

It is “very difficult” to relate soil moisture to tree water use. Plant-based evaluation of water needs is more reliable.

Some have recommended stumping or chainsaw pruning of trees to keep them alive with minimal water. “Don’t do it,” Goldhamer says.

Some irrigation districts are asking growers to take available water early in the season. For almonds, the lack of water late can be deadly.

Many growers have drilled wells to offset the lack of surface water deliveries. Goldhamer suggests mixing available surface water with poor quality well water.

If that is not an option and a grower must use 100 percent salty well water, if there is water to flush salts out of the root zone, there should be little impact on the tree’s production the following season.

Goldhamer’s presentation was aimed at getting growers through 2009 and off to a good 2010 start.

What he did not say was all bets are off if there is a fifth drought year.

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TAGS: Tree Nuts
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