Organic trees fare well in research on almond yields

A 15-year-long comparison of organic and conventional almonds, grown side by side at the Nickels Soil Lab in Arbuckle, has yielded valuable information on key challenges in organic nut production— and what can be done about them.

In the most recent harvest, the organic nonpareil trees produced good-sized kernels. Their yields were not too far short of nearby conventional trees and, despite the absence of any pesticides, there were few rejections for quality issues.

But most important is the information gathered by a team of University of California researchers about major difficulties in making those plots economically viable.

"During the 15 seasons of this trial, organic production levels, disease management, weed control and nitrogen fertility have been the most challenging issues," said John Edstrom, manager at the Arbuckle research orchard when the trial was planted. "Recently, nitrogen nutrition has eclipsed weed control and disease management as the largest, sustained challenge to economically sustainable organic production in this orchard."

The trial has been on a 7-acre block split between conventional and organic areas, both planted in a 3-to-1 ratio in nonpareil and the pollinator variety Fritz.

In 2020, the conventional nonpareil trees approached 2,700 pounds an acre while the organic trees yielded a little more than 2,100 pounds, with kernels that were only slightly smaller.

While the organic nonpareil trees produced a respectable 85% of the yields of their conventional neighbors, that harvest came after considerable head scratching and expenditure on fertilizing the nitrogen-hungry trees.

"Almonds use roughly 60 to 70 pounds of nitrogen per 1,000 pounds of kernel crop, the highest nitrogen use of any tree crop commonly grown in California," Edstrom said. "Maintaining orchard nitrogen status while maximizing organic production is challenging and expensive."

Ten years ago, researchers began injecting various liquid organic fertilizers through the irrigation system and stopped broadcasting yard waste compost, which provides little nitrogen.

"From 2011 to 2019, liquid organic fertilizer 400-2 was injected through the irrigation system," Edstrom said. "This was expensive, and organic treatment blocks were still nitrogen deficient based on summer leaf nitrogen levels."

Last year, researchers made a concerted effort to ramp up organic fertility with a series of fertigated and shanked applications. They included 30 pounds of liquid nitrogen through the irrigation system in March and 100 pounds of nitrogen in feather meal that was shanked in late April.

"Organic production was good, and summer leaf levels were up compared to previous years, although right on the nitrogen-deficiency threshold," Edstrom said.

The difference in leaf tissue nitrogen between the conventional and organic trees in a July sample—2.52% to 2.20%—was measurable, despite a significant investment in organic fertilizers.

Pest damage from navel orangeworms was easier to manage in the organic trees after a rigorous program of orchard sanitation. Implemented at the beginning, it was supplemented in 2020 by a mating disruption program with pheromone puffers throughout the block.

Navel orangeworm damage to the organic nonpareil nuts dropped from 2% to just 0.5% in the first year of the pheromone program.

The Fritz pollinator variety, which harvests later and is more susceptible to navel orangeworm damage, suffered 16.1% damage in the 2017 season. But it also dropped from 2% to 0.5% in the first year of the pheromone program.

"While 2020 was generally a light navel orangeworm damage year and an adjacent hard-shell block was removed the year before, reducing pressure in the organic trial, the low navel orangeworm levels in the organic block are encouraging," Edstrom said. "The plan is to use mating disruption in 2021."

Weeds are another difficult matter. Researchers have struggled to find an organic system that is both effective and economical.

"While propane flaming in the tree row has been mostly effective, it is slow and expensive," Edstrom said.

Some of the organic trees benefitted from installation of a 6-foot-wide cloth at planting, which prevented most weed growth within the tree line.

This practice, however, costs $1,500 an acre at the beginning, with additional repair costs annually. It presented the challenge of trying to control weeds just outside the 6-foot area without damaging the cloth.

"Weeds were hard to control along the edges of the cloth where mowers couldn't operate without catching or pulling the cloth," Edstrom said. "The weed cloth was removed at the end of 2011 after annual maintenance became too expensive and time-consuming to continue."

With the weed cloth experiment abandoned, researchers went back to the drawing board and came up with modifications of the irrigation system that made propane flaming within the tree line more economical.

"The surface drip system was replaced in October 2007 with a dual line subsurface drip system, primarily to reduce weed growth, seed emergence and associated weed-control costs," Edstrom said. "This has reduced propane flaming expenses significantly compared to previous seasons."

The combination of buried drip irrigation and propane flaming largely worked, but the system had to be redone to account for clogged lines invisible below the surface.

"The subsurface drip lines were replaced in spring 2016 due to plugging issues," Edstrom said. "Vented end-caps for each line were installed with the new hoses."

(Bob Johnson is a reporter in Sacramento. He may be contacted at bjohn11135@gmail.com.)