Happily there is a solution in the form of capacitive sensor probes ... which in turn feeds a rectifier to create a DC output. This can be measured to gain a reading of the soil moisture level.

Capacitive: The diaphragm functions as one of two capacitor plates in capacitive sensors ... Advanced signal processing techniques are employed to ensure precise and consistent output.

as well as how capacitive detection sensors. Then you will learn how to specify and use accelerometers in an embedded circuit. We will discuss how the first accelerometers used the piezoelectric ...