Method and device allowing measurement of the state of hydration of soils or of culture media using the fact that the dielectric which the earth (or the culture medium) may constitute varies in proportion with the variation in the quantity of water which it contains. The sensor is therefore a capacitor whose plates are driven into the ground or the culture medium. One of the plates is covered with plastic so as to electrically insulate it in order to prevent the capacitor being converted into an ohmic resistor when the earth is very humid.
