Cover crops have been promoted for their abilities to reduce erosion and retain or enhance soil nutrients. Now there is evidence that they can significantly reduce weed seeds from entering the soil seed bank.
Crops such as red clover, planted after a main crop’s harvest, often are used to provide cover for insects such as ground beetles that feed on weed seed scattered along the soil surface. Beetles remove the seeds before they are tilled under and become part of the field’s long-term seed bank. Rodents are also important consumers of weed seeds and, like beetles, tend to prefer foraging under the shelter provided by cover.
As a result, in fields planted with cover crops, three to four times more weed seed is eliminated from the combination of beetles and rodents, according to recent research.
While that result wasn’t unexpected, two researchers from Purdue University used the field experiments to learn a little more about how habitat and fear might cause ripples along the food chain and affect seed predation.
Beyond eating weed seeds, rodents also attack seed-feeding beetles, making it a challenge to predict seed consumption rates where both mice and beetles coexist. Each faces numerous threats that change their approaches to finding food. On dark nights, for example, rodents might roam open fields. But under a moonlit sky, they are vulnerable to nocturnal predators.
It was to be believed that increasing the amount of light would drive rodents to cover more often, increasing the number of beetles they ate. If that were the case, reducing the beetle population might increase the amount of weed seed left in a field.
In field experiments, they artificially manipulated “moonlight” in fields using lanterns to simulate a full moon. They indeed found fewer beetles under the illuminated cover crops, but instead of reducing the rate of weed seed consumption, the light treatments had no effect.
In lab tests, exposure to a rodent decreased the movement of beetles, likely their way of becoming less noticeable to the predators. But surprisingly, the beetles ate 50 percent more seeds, despite the risk of being eaten themselves.