Using the sun to manage weeds

GLOBAL SOLAR RI Farm
TREATMENT: Almond field being treated with biosolarisation. (Photo: University of California, Davis)

EXPERIMENTS with biosolarisation – a process combining the sun’s heat with soil amendments to manage weeds and other pests – are showing promise for conventional and organic farmers.

Researchers at the University of California, Davis, are looking at using crop byproducts such as skin, seeds and hulls from fruit, vegetable and nut processing, to generate alternatives to chemical fumigants.

Food science and technology professor Christopher Simmons, who is testing biosolarisation with various crops, says it looks promising.

“Biosolarisation is showing real potential as a safe, sustainable way to control pests while improving crop quality and yield,” he says.

Many backyard gardeners know of solarisation. When they lay a clear plastic tarp over moist soil, they trap solar radiation and heat the soil enough to kill weeds and other pests. But it can take four to six weeks – too long for commercial fields to lay fallow.

Biosolarisation can accelerate and improve the process.

Simmons adds organic amendments such as grape and tomato skins or ground nut hulls to the soil before tarping it to promote beneficial bacteria. They temporarily make the soil more acidic and less hospitable to weeds and pests.

The microbial activity can reduce the treatment time to days.

“By activating beneficial microbes in the soil, biosolarisation has the potential to improve soil health over the long term,” Simmons says.

But for farmers to adopt biosolarisation as an alternative to chemical fumigants, the treatment must be effective, predictable and economical.

Simmons is testing biosolarisation with a variety of crops, amendments and soils against different pests in various locations at commercial scale throughout the state.

“We have field trials underway with lettuce, tomatoes, melons and various cover crops,” Simmons says.

“And we have a long-term, 10-acre trial with almonds at a conventional orchard.”

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