The Almond Board of California and UC Davis have teamed up again. This time the cause is soil fumigation.
After an orchard has passed its productive life, the trees must be taken out. Prior to planting a new crop, the soil must go through “disinfestation” steps.
Parasitic nematodes are one of the pests growers target. Also known as “root-eating” nematodes, these little microorganisms can wreak havoc on an orchard, significantly affecting a crop’s annual production.
There are many ways growers disinfest. It is vital all roots from the previous orchard are removed. Growers will also plant other crops like mustard or sudangrass because of the nematocidal properties.
Perhaps the most efficacious, expensive and controversial method of disinfestation is chemical fumigation.
This practice has been the norm for some time but is falling out of favor in California. Even though growers adhere to strict application laws, many of us are convinced that fumigants are being weened out of the market; the chemicals are either being banned outright or the process is being made so costly that we opt to skip this step altogether.
Chemical fumigation applies gassing agents to the soil. The practice has a high efficacy, killing the most harmful pathogens in the soil. However, an overlooked aspect of chemical fumigation is what the process does to helpful attributes to the soil.
Other beneficial microorganisms — which are essential to nutrient conversion and fighting plant diseases — fall prey to the gases. Think of it like carpet bombing the enemy and having a high percentage of civilian casualties because of collateral damage.
So, what do growers do in a situation like this? We innovate.
Over the past several years, the Almond Board and a team of USDA and UC Davis researchers have been exploring alternatives.
Six months ago, colleagues from the Almond Board and I met with researchers at UC Davis, including Christopher Simmons. Simmons is working on a new soil disinfestation treatment the Almond Board has recently funded as is part of its larger research effort. I was astonished at what I heard at the meeting.
The theory was simple: Take almond hull and shell, mix it in the top layer soil, irrigate, place clear plastic over it and wait. Simmons calls it biosolarization — using biological properties and the power of the sun to combine for a potential alternative to chemical fumigation.
Through the process of biosolarization, microorganisms get to work. They begin to eat the almond hull and shell to produce microbial fermentation — the soil literally begins to ferment under the plastic. During this process, oxygen is stripped from the soil layers. These conditions create a hostile environment to target pests.
Furthermore, passive solar heating penetrates and remains trapped under the clear plastic. The heat disperses through the soil by means of the water applied at the beginning of the treatment. Temperatures can reach 140 degrees or higher.
If I were a conventional grower reading this I would say to myself, “There is no way this could be as effective as methyl bromide, chloropicrin or telone.”
Let’s just wait for the data to come back.
Not only does this technology have the potential to fumigate naturally, it also adds organic matter back to the soil. At the same time, it has high potential to be a new market for almond hull and shell — a win, win.
As a grower research cooperator on the project, Simmons and I have been discussing the possibilities. Though we are still in the hypothesis stage, should the results be favorable, this technology could be deployed in other crops as well.
Many agricultural industries in California are dreading the day, too, when chemical fumigation is gone for good. Biosolarization may provide a cost-effective, environmentally friendly and favorable solution.
Preliminary results of the biosolarization collaborative study between the Almond Board and UC Davis will be presented at this year’s Almond Conference, Dec. 5-7 in Sacramento.