Groundwater Salinity Impacting California Almonds
Millions of years ago, the Central Valley was an inland sea, and sharks were swimming through Bakersfield.
Eventually, that inland sea receded and fresh water from snowpack, floodwaters and estuaries began displacing the salty water in the area’s aquifer, pushing it out toward the west, explains Blake Sanden, farm advisor with the Kern County Cooperative Extension.
Now almond growers – particularly those on the west side of the Valley, who are relying more heavily on groundwater irrigation – are dealing with the ramifications of saline water. “The initial disposition of why the west side is salty in the unconfined aquifer on top, and why the east side is not, is just the whole nature of ancient geology,” Sanden says.
But we’ve actually made it worse through the drilling of wells and our ability to import water from the California aqueduct 450 miles to the north. “Now what you’re doing is creating a net import of salts into the south Valley for which previously, the only recharge into that unconfined groundwater pumping aquifer was the snowmelt runoff and rain,” Sanden explains. “This is more than an additional million tons of extra salt a year being imported by that aqueduct water down to the different water districts that are using that aqueduct water.”
The Impact Of Salinity On Almonds
Crops such as cotton, alfalfa, and even pistachios can handle some salinity, but almonds tend to suffer, because they don’t have the ability to generate a high level sugar and electrolyte concentration in the roots, Sanden explains.
“As the salt concentration in soil goes up, the osmotic resistance to water movement into the roots increases,” he says. “The plants can’t pump water into the roots.”
In addition to total salinity, Sanden says almonds growers have to be concerned about specific ion toxicity, which comes from sodium chloride and boron. “If you have high boron and you’re growing almonds, you have big problems,” he says. “As little as five pounds of soluble boron per every acre foot (of water) can cause trouble in almonds.”
Sanden says there are some engineering outfits trying to develop inexpensive ion exchange scrubbers to pull the boron out, but an economical way to do it has not yet been discovered. Others have been toying with using reverse osmosis for salt mitigation, but so far, no one has developed an economically practical system for agricultural irrigation purposes.
There are some things growers can do, though, to mitigate the risk of adverse effects from saline water. Soluble calcium helps displace soluble sodium, for example, so gypsum can be applied to reduce the amount of soluble sodium present. Gypsum also improves the soil structure to help with leaching.
“When you have an increased salt load, you need to increase the leaching factor of what you’re pushing below the root zone,” Sanden says. “If we have drought conditions, where we only get a couple or three inches of rain, and it’s not enough with just the rainfall to push salts out of the root zone, then you, as a grower, have to apply extra water to accomplish leaching.”
In addition, Sanden says there are some wetting agents that can be used to help water move through the soil more easily.
In the meantime, “pray for rain,” he says.