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Post-WOR planting has its challenges

Todd Fitchette TNFP0902-fitchette-post-wor.jpg
Replanting almonds after whole-orchard recycling has its own challenges, a University of California expert says.
Potential diseases, carbon in soil are among them, UC expert says.

As an educational institution, University of California, Davis has a goal to reach carbon neutrality by 2025 and recent release of one of their latest studies shows one pathway --- orchard recycling --- that produces soil health improvements and increased yields.

In the school’s independent, student-run publication, The California Aggie, Brent Holtz, UC cooperative extension county director and farm advisor for San Joaquin County, espoused the practice.

After studying WOR for over a decade while witnessing potential benefits of the practice on his own family almond farm, he noted that implementation of more strict air quality regulations took away the option of traditional on-site burning of trees.  “Growers needed an alternative to a sort of biomass crisis,” Holtz told the newspaper about the benefits of whole orchard recycling.

UC Davis data showed researchers reporting a 58% increase in soil carbon as well as a 32% increase in water-holding capacity — in addition to an overall productivity increase of 20%.

Already popular and growing increasingly so, the WOR process is a viable option as the Almond Board of California reports as many as 40,000 acres of almond orchard are expected to be removed in the next decade.  9,000 acres of almond trees were removed last year.  Other pertinent numbers to take into account — there are 1,260,137 acres of bearing almonds in California, 88,000 of which are two decades old and beginning to appear on the to-be-removed list.

“Soils in California, especially in San Joaquin County, tend to be very low in organic matter,” hence a need to increase soil health, Holtz told the campus paper.

The recycling concept was one of the agenda items at a recent 2021 Almond Day virtual event where Mae Culumber, UC Cooperative Extension Farm Advisor in Fresno County, addressed the issue of Planting New Orchards After Whole Orchard Recycling.

“Whole orchard recycling and replanting comes out of a time of necessity due to increasing regulation with regard to air quality measures, especially in the San Joaquin Valley,” she told Western Farm Press.

“With burning permits being phased out by 2025, the acreage involved will need an alternative method of disposal and we’re looking at incorporating the majority of those removed orchards back into the soil.”

A few problems

Replanting in WOR orchards isn’t without a few problems of its own, however.  “Nutrition is one of the first concerns that comes up — how these ground-up wood chips will impact nutrient availability for the next orchard crop,” she says.

“There needs to be a ratio between carbon and nitrogen in the soil, like a 25-30 to 1 ratio and when you put all those wood chips in the ground, it makes the soil closer to about 400 to one because those ground-up orchard trees are made up of about 50% carbon,” she says.

“Microorganisms start to decompose the chips, but they need energy to do so and they get that energy from carbon and nitrogen.  If there’s a big imbalance, the microbes will immobilize any available nitrogen and thus will compete with the young tree roots.  That imbalance diminishes quickly, within a year or two, but in the initial time when you’re planting young trees in chip-laden ground, more attention needs to be paid to nutrition needs than would probably be needed in a conventionally-planted orchard.”

And while nutrition may be the number one concern, so, too, are potential diseases, like the fungal decay nemesis, ganoderma, that has been around the southern San Joaquin Valley for decades.  “If there has been a history of disease in a removed orchard, there’s always a question of whether or not it is going to reside in the soil, even with fumigation,” she says.  “A lot of times it depends on the pathogen and if it’s soil born, whether those spores can survive and live in the soil.

“Preliminary research on the size of wood chips indicates chips about tub-grinding size are small enough to where the inoculum won’t survive past a couple of months.”

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