Listening to the life in your soil

While most of us are aware that biology is the most important determinant of soil health, measuring it can be time consuming and requires expertise. This can also be destructive because you have to remove the sample of the soil to examine it. You’re never able to monitor the same piece of soil in situ.

Acoustic sensing has the potential to revolutionise these soil measurements. Using a specialised microphone attached to a probe, the sensor monitors and records the sounds and vibrations made by the macrofauna in the soil. This includes earthworms, springtails, mites, centipedes, millipedes, beetles and ants. These are then recorded, the precise location tagged using GPS and sent to a database. These patterns of waveforms can tell us what is there, how active it is and also how it is distributed.

The technology still has some challenges to overcome. The outputs from the microphones are quiet, with a lot of background noise, so can be difficult to analyse. Machine learning can help with this, but there needs to a level of human expertise to set it on the right path. 

Once developed, however, the technology has the potential for many practical applications. For example, it could be used to monitor earthworm activity windows so soil cultivations are scheduled to mitigate harm. Wave propagation techniques could estimate the structural resilience of the soil to compaction, to inform suitable vehicle loads and minimise disruption to soil structure (1).

Soil acoustics has also been used to get the public more engaged with soil biology. In Switzerland, they ran a ‘Sounding Soil’ exhibition - an immersive art installation, where people could walk into a darkened shipping container and experience the complex acoustics of soil biology in many dimensions (2).