With almond harvest underway in many parts of California, it’s time to formulate a post-harvest orchard management to-do list of tasks to be completed by year’s end to optimize next year’s harvest.

Irrigation and maintaining proper soil nutrition for the trees is top of the list. Key nutrients that need to be maintained include potassium, nitrogen, boron and zinc.

“We’re coming off of two years of large back to back almond crops, and that can deplete the nutrients in soil dramatically,” says Wes Asai, owner of Wes Asai Pomology Consulting in Turlock, Calif.

California almond producers harvested more than 2 billion last year, and the Aug. 10 forecast from the National Agricultural Statistics Service predicts a 2.1-billion pound harvest this year.

Feed the tree

Just how much can almond production drain soil nutrients?

In a study for the California Almond Board last year, Patrick Brown and other University of California, Davis, researchers reported that almond production can remove as much as 80 pounds of potassium and more than 65 pounds of nitrogen from the soil for every 1,000 pounds of kernel.

“Usually, sulfate of potash is applied post-harvest,” Asai says. “Potassium is vital to sustaining high yields. We want to sustain potassium above critical levels since potassium deficiency can impact productivity for years if it goes uncorrected.”  

Typically, potassium leaf levels should be a minimum 1.4 percent, but, “many growers believe that with higher yield goals, they should maintain the level higher than that—2 percent or higher, he says.

A 2001 study by Brown and another group of UC Davis researchers found that trees with less than 1.4 percent potassium in a July leaf sample experienced a 27 percent increase in spur mortality and a 30 percent decrease in return bloom of fruiting spurs the following year.

Match nitrogen to nuts that were harvested

In addition to potassium, nitrogen levels should also be assessed, says David Doll, a University of California Cooperative Extension farm adviser in Merced County.

“Those are key things to do immediately post-harvest,” he says. “Get the irrigation going and if yields were as high as originally planned, then add the final 20 percent of your seasonal nitrogen program immediately post-harvest.

“If yields were lower than originally planned and July leaf values were adequate, then a reduction in post-harvest nitrogen should be considered. Remember, your goal is to apply nitrogen at an amount that reflects what was removed from the field in the crop.”

Doll says that the fall is good timing for boron and zinc foliar treatments.

“If you do it now, you won’t have to do it in the pre-bloom timing,” he says.

A fall application of boron, in particular, is more effective, because the leaves are still on the trees—meaning the tree gets more of this micronutrient because it has a larger treatment surface.

Other post-harvest chores 

Walking through orchards to scout for pests and disease post-harvest is important as well.

“For example, if we see rust on the leaves, we would want to apply zinc sulfate to knock the leaves off of the tree and get that rust inoculum on the ground, where it will break up,” Doll says.

Applying 30 pounds per acre of zinc sulfate to drop leaves is recommended in late October to early November, he says.

Scouting orchards during this period can also reveal irrigation issues that may mean repairs or that irrigation systems need to be moved to be more effective.

Doll recommends says this post-harvest time also is an ideal time for pruning, if needed.

This article was prepared on behalf of Great Salt Lakes Minerals.