An alternative crop rotation may provide farmers with a new way to fight weeds.
In a study published in Weed Science, Katriona Shea calls it “weed-weed competition.”
She said stacked crop rotations, such as corn-corn-soybean-soybean-wheat-wheat, could suppress weeds without increasing inputs.
“The idea is basically do what you already do, but in a different order rather than trying to do more of it,” said Shea, a professor at Pennsylvania State University.
The promise of stacked rotations, in which crops are grown consecutively, typically two years at a time, followed by a longer-than-normal break, has been mentioned in farm journals and at meetings but has received little research funding.
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Shea used a numerical model to conduct simulations, testing different rotations against different groups of weed species. She said the results, while encouraging, are not based on empirical field evidence and don’t consider potential problems such as disease.
Shea’s simulation found that the stacked corn-soybean-wheat rotation decreased weed seeds by 15 percent. Similar trends were ob-served in other rotations where weeds grew during the same season.
The study acknowledged that the decrease isn’t huge but suggested it could contribute to an integrated weed management program.
Shea noted it’s potential in organic systems.
“They think about the weed hurting the crop, but they don’t think about the idea that they might actually interfere with each other and that potentially it’s possible to use that,” she said.
American researcher Dwayne Beck suggested in a publication from the Dakota Lakes Research Farm in South Dakota that stacked crop rotations could slow the development of resistant weeds and insects by promoting diversity through long breaks.
“From a diversity standpoint, it is better to have a mixture of intervals,” Beck wrote. “To provide maximum protection against pests with short cycles, one of the intervals must be sufficiently long to allow populations of certain diseases or weeds to drop to low levels.”
He said stacked rotations may keep pest populations diverse — what he called “confused” — and allow for a mixture of short and long residual herbicides. However, he said the subject has not been thoroughly tested and may not work with all rotations.
Shea said it’s a topic worthy of further study.
“If we model it, it shows an impact and that’s really promising,” she said.
“If we’d modelled it and it didn’t show anything, we’d just say, ‘don’t risk it,’ but this suggests it’s worth doing more.”
