The air and the water are known to be filled with the sounds of many living things. But how is that in the ground? Do organisms make themselves noticeable there through sounds? Apparently yes, according to a study: Using sensors, biologists can record the fine noises that roots make when growing or worms when digging tunnels. The acoustic evidence is apparently even suitable for assessing the quality of soils.
The more active it is in the soil, the better: Above all, the rooting and the activity of earthworms are of great importance for the efficiency of the literal basis of ecosystems and agriculture. Against this background, information about soil life and the relationships in this ecosystem is very important. What is happening underground is, however, comparatively difficult to grasp, because in order to obtain information you have to dig and evaluate. But as the researchers working with Dani Or from ETH Zurich have shown, you can evidently track life in the soil using acoustic technology.
As part of their study, they compared visual observations with acoustic measurements. To do this, they used earth-filled glass vessels that allowed glimpses into the ground. In some they planted corn plants and dig tunnels in others. In addition, there were piezoelectric sensors in the test units. These technical elements are able to detect signals that are inaudible to humans – elastic waves with a frequency of 1 to 100 kilohertz. They arise, for example, when grains of sand shift or small cracks form.
The root cracks and the worm crunches
To check whether the signals picked up by the piezo sensors have anything to do with biological activity, the team compared the observed root growth and the worms’ burrowing activity with the recorded noises. It turned out that the visual observations were largely in agreement with the acoustic measurements. Results from control units filled with soil only confirmed that the noises must actually come from the roots and worms. “The noises also have a certain signature so that they can be assigned to a specific source,” says Or. “Worms, for example, move much faster than roots, and at the same time their acoustic emissions are much more selective.”
Listening to the soil could be worthwhile, say the researchers: “For example, we can find out when and under what conditions roots grow. With this method, we can record this relatively easily on the spot – without digging ”. The method could also provide information about the formation of soil structures and the interaction between worms and root growth, say the scientists.
Source: ETH Zurich, specialist article: Scientific Reports, doi: 10.1038 / s41598-018-28582-9