Researchers Study Almond Rootstock Salt Tolerance

The continued drought means more growers are relying on groundwater, which, depending on location, can be quite saline. Consequences of salty water on almonds include leaf burn and defoliation. But, some rootstocks might be more tolerant of salt.

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Patrick Brown, professor of plant sciences at the University of California-Davis, has been working with colleagues to test the salt-tolerance of various rootstocks to determine which, if any, can withstand increased water salinity. They’re also studying ways growers can manage water such that the salinity effects are minimized on the trees.

“It’s very clear that there is a tremendous variety of response to salinity in Californian rootstock material,” Brown says. “The traditional material that’s most widely planted is Nemaguard, and actually, among the common rootstocks, that’s probably the poorest in terms of tolerance to salinity.”

Brown says to date, the best materials they’ve tested include Viking and Empyrean. “Their level of tolerance to salt and chloride is really remarkably better than Nemaguard,” he says.

“We’re also working on screening methods, so that new rootstocks, as they come along, can be screened for their potential tolerance to salt so that growers, when they make an investment in an orchard and plant the orchard, they can be assured that they’re planting the best possible rootstock for the challenges they have,” he adds.

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What’s The Problem With Salinity?

In addition to testing various rootstocks, the researchers have been working to identify what it is about salinity that damages trees. “It’s well known that salinity can be a problem because it induces water stress, but salinity can also be a problem because the plants are sensitive to high levels of sodium and chloride,” Brown says. “In the studies that we’ve been doing to date, it appears that the most important factor, first and foremost, is the chloride, and then the sodium. The salt-induced water stress from excess salinity, while it is important, is not as important as the toxicity caused by those ions.”

The researchers are also working on gaining a better understanding of the biology of salt and how it moves around the plant. “That will also help us understand better how to manage and mitigate the problem,” Brown says.

Irrigation Management

As almond ground continues to expand and water becomes more scarce, Brown and his colleagues determined it was also important to study irrigation management and how certain practices might minimize the impact of saline water. They’re currently in the process of determining when to use poor-quality water versus good-quality water, and how using the right water at the right time could mitigate the effects of salt.

Brown adds that salinity and nitrogen management are very closely tied together. “When you have access to adequate or greater than adequate levels of water, such as during the winter, the standard strategy (for managing salinity) would be to apply large volumes of water and wash the salt out of the soil,” he says.

However, that approach can put at risk the leftover nitrogen in the root zone, which could leach into the groundwater supply. “It’s pretty clear that growers are going to have to think of managing salinity and preventing the loss of nitrogen through the bottom of the profile at the same time,” Brown says. “And that’s a new context that most growers will not have thought about, and it’s going to take some clever strategies and some good education to make sure we can manage both those things at the same time.”

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