An impressive tree grinding demonstration showed growers the possibility of capturing organic matter from orchard removal. University of California Department of Agriculture and Natural Resources hosted the event where IronWolf showed how their machine works. Cooperative Extension Farm Advisor Brent Holtz talks about the research.
More About the Research
Whole Orchard Recycling — An Alternative to Burning, Cogeneration?
From the Almond Board of California: As more cogeneration plants are shutting down, growers are being forced to consider alternative methods for dealing with tree biomass upon orchard removal. One of those alternatives is grinding up whole almond orchards and incorporating the tree biomass into the soil, leading to the question of how this additional organic matter affects the soil, and more important, how it affects the health of a subsequent almond orchard planted in these soils.
This was the subject tackled by farm advisor Dr. Brent Holtz, UC Cooperative Extension, San Joaquin County, in a session on soil quality at last December’s Almond Conference. The initial years of this research were funded by Almond Board of California.
Shredding Trial
Holtz reported on a trial involving shredded prunings conducted in Madera County beginning in 2003 and funded by the Almond Board of California. Shredded prunings were incorporated 1–2 inches into the soil, and after 11 years, several benefits were realized, most notably, higher soil nutrient levels, lower pH and more organic matter (OM). The OM bound up sodium to the extent that leaves had up to half the amount of sodium compared to the control.
In additional studies, trees were planted in containers with one-third wood chips and two-thirds soil. In two years, several benefits accrued to containers with wood chips:
All nutrients in the soil were significantly higher; Water infiltration was significantly faster, and trees showed less water stress, as the chips were holding water in the soil; Organic matter increased from less than 1% to 5%; and Carbon levels increased from 0.5% to almost 3%.
Whole-Orchard Incorporation
With these benefits of a high wood chip–to-soil ratio established, Holtz turned to the possibility of removing whole orchards and incorporating OM without significantly affecting the next orchard.
Using an “Iron Wolf,” a 50-ton rototiller capable of grinding whole trees and incorporating chips into the soil, whole peach trees in an old orchard were shredded and incorporated in plots, with trees in other plots burned and the ashes spread on the soil surface. Almond trees planted in both plots were fertilized normally.
By the third year, the nutrients were significantly greater where trees had been ground and incorporated, a trend that continued through three more years of the trial.
The whole-orchard chip incorporation treatment resulted in increased organic matter, soil carbon, nutrients and microbial diversity, including beneficial fungi, as well as increased water-holding capacity of the soil.