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A gritty new tool in the war against weeds

Weed and feed your crop with blasted soybean meal

Researchers with the University of Illinois have come up with a new tactic in the war against weeds: blasting.

“Abrasive weeding,” a strategy that may prove most useful for small-scale organic growers, is proving to be “surprisingly effective,” university researchers say in a release.

In conjunction with plastic mulch, abrasive weeding reduced final weed biomass by 69 to 97 per cent compared to non-weeded control plots, said agroecologist Samuel Wortman.

Abrasive weeding uses an air compressor to blast weed seedlings with organic grit. In the University of Illinois study, grit was applied through a hand-held siphon-fed sand-blasting unit connected to a gas-powered air compressor, the release said. It was hauled down crop rows with a walk-behind tractor.

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A number of grit sources were tried including walnut shells, granulated maize cob, greensand, and soybean meal.

Wortman said he found no significant differences between the grit types in terms of efficacy. “When it leaves the nozzle, it’s at least Mach 1 (767 m.p.h.),” Wortman noted. “The stuff comes out so fast, it doesn’t really matter what the shape of the particle is.”

Researchers said it is important to use this type of treatment on transplanted crops that are substantially larger than the weed seedlings. But despite some shredding damage to the crops, yields were 33 to 44 per cent greater yields than in non-weeded control plots.

An additional benefit of weed blasting is the potential for growers to use organic fertilizers, such as soybean meal, as blasting material. “We expect that abrasive weeding could contribute between 35 and 105 kg nitrogen per hectare to soil fertility.” The idea that a grower could both fertilize and kill weeds in a single pass is appealing, but the researchers cautioned that it is still unknown whether the fertilizer would be available for plant uptake within critical windows.

Testing is continuing on different horticultural crops, including broccoli and kale, with and without additional weed control methods. “Early results suggest that the presence of polyethylene mulch or biodegradable plastic mulch strongly enhances the success of weed blasting, as compared with straw mulch and bare soil,” the release said.

Because ricocheting particles can pose a risk to the applicator, Wortman advises using protective eyewear.

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