Plants grow faster when exposed to vibratory noise

Vibrations in the earth, caused by human activity such as traffic, industry and wind turbines, affect the soil and influence processes such as plant growth. This is the conclusion reached by fieldwork and lab studies conducted by a team of researchers at VU Amsterdam, led by biologist Wouter Halfwerk.

05/03/2021 | 10:00 AM

Not only did the plants in the studies grow faster as a result of these vibrations; they also flowered and began to bear seed earlier. However, the researchers also found fewer earthworms in locations affected by high levels of vibratory noise. These and other findings were recently published in the scientific journal Oikos and on the BioRxiv website.

Causes of ground vibrations
Volcanic activity, earthquakes and the shifting of tectonic plates constantly cause vibrations in the earth’s surface. Human activities have also been shown to cause vibrations, picked up as ‘seismic noise’ by measuring equipment at seismic stations. In an article published in leading journal Science last year, Halfwerk argued that the extent of the human contribution to these vibrations only became clear during the first Covid lockdown in March and April 2020. In those months of restricted human activity, seismologists worldwide reported a fifty percent drop in ground vibrations compared to pre-lockdown levels. 

Plant development
Much has yet to be discovered about how human-induced vibrations affect the development of plants and herbivorous life forms in the soil. Researcher Estefania Velilla, who obtained her doctorate on aspects of this research, explains, “In our fieldwork and lab studies, we studied the effect of subsurface vibrations near wind turbines, not only on soil life in general but also more specifically on the interaction between plants, soil fauna and insect pests.” 

Measuring vibrations in the field
To study these effects in a controlled environment, the researchers first carried out seismological measurements in a test field. Two organic farmers in Flevopolder, who have seven wind turbines on their land, were willing to facilitate the research. This enabled the scientists to map the vibrations caused by wind turbines at various distances and depths. The vibrations measured were then simulated in the Ecological Science lab at VU Amsterdam. 

Faster and larger
In the lab, the researchers exposed pea plants (Pisum sativum) to high and low levels of vibration. They then measured germination, flowering and fruiting and daily growth in shoot length. Lead researcher Wouter Halfwerk, “We found that plants exposed to high levels of vibration grew significantly faster and larger than plants exposed to lower levels of vibration. Moreover, the plants exposed to considerably more vibration germinated, flowered and produced at a faster rate than those exposed to less vibration.” 

Further research needed
“Our results could be of great interest to farmers, especially in the organic sector, where healthy levels of soil fauna are often still present,” Halfwerk adds. “Further research is needed to identify the effects on wild plants and agricultural crops. Follow-up studies are also needed to discover how earthworms are affected by ground vibrations. Field measurements suggest that vibrations have a negative impact on the presence of earthworms. We want to find out what causes this.” One theory, Halfwerk explains, is that the vibrations make it easier for moles to catch earthworms. “Another possibility is that earthworms mistakenly read the vibrations as a sign that moles are present and seek refuge elsewhere.”