Can almond tree varieties be watered differently?

Editor’s note: This story is being reprinted to correct errors in the original.

Almonds and water ... both big concerns for the Yuba-sutter-colusa area. Almonds constitute one of the area’s top crops; and everyone’s anxious about the next water shortage and its effects on crops.

So there’s natural interest in a college graduate student’s project looking into how varying amounts of water affect almond yield.

In Yuba County, almonds were ranked No. 9 in leading commodities in the 2017 crop report, having a crop value of $5.5 million. Almonds were ranked No. 6 in Sutter County with a crop value of $36.2 million. In Colusa County, almonds were the top commodity with a crop value of $301.2 million in the 2016 crop report (the 2017 report has not been released).

Franz Niederholzer, pomologist at the UC Davis Cooperative Extension Office, said almonds do well here because they do well in a Mediterranean climate – warm summers and mild winters. He also said water is extremely important to almond production and knowing how different levels affect the crop could be valuable to growers.

Kelley Drechsler, a graduate student at UC Davis, has been working at the Nickels Soil Lab in Arbuckle, which is overseen by the UC Davis Cooperative Extension Office. She has been working with her professor, Isaya Kisekka, to see how different water levels affect different varieties of almonds.

Niederholzer said the Nickels estate is a privately owned research facility that works with the water district, local growers and the University of California.

There are three different varieties in the five acre orchard Drechsler is working in, she said. The Nonpareil is the type most people eat, while the other two, Aldrich and the Butte are mainly for pollination, because they don’t always yield as well as the nonpareil and taste different.

“Most growers irrigate for the nonpareil,” Drechsler said. “... What I’m doing is I’ve interfaced the irrigation system so I can independently irrigate each variety.”

She said that the growers typically water all three varieties with the same amount of water. But, the idea behind the experiment is to see if the three different varieties should be watered differently for a better yield.

“With climate change and water limitations, we’re getting to the point where irrigation management might need to be more advanced,” she said.

Part of the project requires Drechsler to measure the tree response to four different irrigation levels for the three different varieties.

She said she is working on the stem water potential, which is a good standard for measuring plant water status – they take a leaf off the tree, subject it to pressure inside a pressure chamber and the water bubbles out of the stem.

According to UC Davis, the leaf is placed in the pressure chamber and part of the stem is left outside the chamber. The pressure that is applied until water is seen, that’s its stem water potential. The more pressure, the more water stressed it takes to push the water out, the more water stressed the tree is and the more irrigation it needs.

Drechsler said she will also be measuring the yield and quality parameters as in kernel weight, dimensions, presence of mold and diseases.

The current results on the differences in yield from the different treatments and quality will be presented in December at the Almond Conference in Sacramento.

However, Drechsler said the best result will come next year because this year’s experiment will affect next year’s yield.