An apparatus for assessing at least one property of a target soil responsive to a first a first microwave signal, constituted of: a detector; a probe arranged to be embedded in the target soil; and a coupler arranged to couple a first portion of the first microwave signal to the first end of the probe, and to couple a second portion of the generated first microwave signal as a microwave reference signal to a reference input of the detector; the detector arranged to square each of the microwave signal exiting the probe and the microwave reference signal and to output a phase difference signal indicative of the phase difference between the squared probe output microwave signal and the squared microwave reference signal; and a control circuitry coupled to the output of the detector and arranged to output an irrigation control signal responsive to the phase difference signal.