Swiss and French researchers have succeeded in obtaining acoustic signals that correspond to growing roots and burrowing earthworms with the aid of piezoelectric sensors.
The special sensors can measure elastic sound waves from 1 to 100 kilohertz that humans cannot detect. These are sounds are equivalent to rubbing small grains of soil together or cracks forming in the soil.
The sensors were placed in glass containers filled with sandy soil containing corn plants and loamy soil with earthworms. After a few days, the scientists were able to compare root growth and burrowed tunnels with the acoustic signals registered by the sensors. They were highly consistent and control measurements from containers without plants or earthworms confirmed that the sounds originated from roots and earthworm activity.
“We can learn when roots grow, for example. Until now, we didn’t know whether it happens during the day, at night, or in wet or dry soil conditions. The new method allows us to find this out on site relatively easily - and without digging,” said Swiss study leader Dani Or of the Swiss Federal Institute of Technology in Zurich (ETHZ).
Experiments in field conditions are planned and it is hoped that the findings will one day aid farmers in soil analysis.