How We Grow

2019 May/June How We Grow

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6 A L M O N D O R C H A R D 2 0 2 5 G O A L S ZERO WASTE Whole Orchard Recycling Holds Promise, More Research Needed Whole Orchard Recycling (WOR) is a practice gaining traction among almond growers who no longer have access to a cogeneration facility or are looking for an alternative to burning woody biomass. WOR involves grinding whole almond trees into small chips, spreading them evenly over the ground, and then disking them into the soil. Preliminary research indicates WOR can increase soil organic matter, improve water infiltration and retention, aid in carbon sequestration, boost yield and help the industry reach its goal of achieving zero waste in almond orchards by 2025. WOR has shown great promise for almond growers, but there are still some conditions where more research is needed to determine if this is a beneficial practice. The main learning to date is that growers need to apply additional nitrogen in the first year of WOR to overcome the soil microbes' use of available nitrogen. The main concern is whether or not it is appropriate for certain diseases to remain existing in the previous orchard — such as oak root fungus (Armillaria), butt rot (Ganoderma) or crown gall (Agrobacterium) — as the chipping and spreading of trees may actually assist in spreading said diseases within the orchard. "Whole Orchard Recycling data, to date, has only focused on recycling almonds and stonefruits, so it is difficult to extrapolate its use for other tree or vine crops due to differences in the wood, as well as in susceptibilities to wood diseases," said Gabriele Ludwig, Ph.D., director of Sustainability and Environmental Affairs at the Almond Board of California (ABC). Researchers also have questions about how best to chip and incorporate the wood into the soil. Current recommendations are to chip to 2 inches or less to allow for faster breakdown of the wood in the soil. However, some might argue that a slower release of the wood's nutrients, coming from somewhat larger chips, aligns better with almonds' development, a period of the lifecycle when almond trees' demand for nutrients is at its peak. Still, current research and the teams who support it are making encouraging strides in finding answers to the industry's questions. Studies underway Two large ABC-funded WOR studies involving several scientists at the University of California and USDA Agricultural Research Service are currently underway. Among those scientists are Mae Culumber, a University of California Cooperative Extension (UCCE) farm advisor from Fresno County, and Brent Holtz, San Joaquin County's UCCE director and farm advisor. ABC funds have also been leveraged to receive additional funding from a California Department of Food and Agriculture (CDFA) and USDA Specialty Crop Block grant, as well as a CDFA Healthy Soils Initiative Demonstration grant. "The researchers are working as a real team to study soil and microbial systems, greenhouse-gas emission effects, carbon sequestration, disease and nematode trends, and other agronomic data," Ludwig said. "We also expect their work to lead to improvements in technology to incorporate ground-up trees more efficiently. Right now, the WOR practices being used in commercial orchards are relying on grower ingenuity." Holtz, who has doggedly explored adding wood chips to the soil for A modified spreader and rototiller are used to incorporate almond wood chips into a field where almond trees once stood. "It's costing about $1,000 an acre to grind up orchards and put the wood back into the ground." – Brent Holtz

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