The idea of grinding old orchards into wood chips and recycling them into soil has seized the interest of California’s almond industry, which sees the potential for environmental and economic benefits.
Although more testing remains to be done, initial findings suggest the process can boost soil nutrients, promote water retention and reduce salinity, a growing problem in the southern Central Valley’s drought-stricken almond acreage.
One particularly encouraging aspect of the process, an Almond Board of California official said, is how it eliminates the need to burn or otherwise dispose of woody ag waste. That has been a rising concern as hard times hit California’s biomass-fueled power plants, where the bulk of the state’s old almond orchards have been sent in recent years.
Researchers at the University of California Cooperative Extension and UC Davis recently applied for money from the board and the federal government to continue experimenting with the process. Grant awards could be announced soon.
A plant pathologist who has done research on grinding up trees and returning them to soil, UC Cooperative Extension farm advisor Brent Holtz, delivered a presentation on the process at the almond board’s annual conference in December. In it, he likened the approach to what happens naturally in forests, where dead trees productively decompose into soil.
He told the audience about a peach orchard that was ground up several years ago and then, using a large machine called an Iron Wolf, tilled a foot and a half into the soil. Holtz tracked how well that soil produced new trees, as compared with the performance of trees fertilized with burnt wood waste.
The almond board’s director for sustainability and environmental affairs, Gabriele Ludwig, said conventional wisdom was that the burnt waste would provide better nutrition for the trees. And it did, but only for the first couple of years, after which time the soil amended with ground trees grew more healthy than the others.
Better yet, Ludwig said, an irrigation accident showed an added benefit. After more than a month of no watering, the trees living on extra-woody soil fared better.
“To me, that was an inadvertent mistake that was a very valuable mistake,“ she said.
Several things about the approach remain unclear, Ludwig added, such as whether it works in different soil types and whether grinding up and recycling diseased trees can end up hurting the generation that follows.
Also, analyses need to be done on whether recycling old almond orchards provides as much net benefit, in terms of measures like energy and greenhouse gas emissions, as other methods of disposal, including turning the trees into biochar and burying that.