The researchers used "[...] custom microsensors that detected changes in the mud’s chemistry." I have been toying with the idea of analysing the composition of

The researchers used "[...] custom microsensors that detected changes in the mud’s chemistry." I have been toying with the idea of analysing the composition of soils for house plants etc, but never had the time to actually dig deep enough to get started working on it. My shallow searches for raspberry pi sensors was not super succecssful (they do exist, but most projects seem old and abandoned) Are there any affordable sensors out there that can be used to analyse soil samples? Alternatively, what knowledge is required to build sensors that can detect chemical composition of soil?