Hi - One thing you need to watch is earthing. The probe signal currents are very low so an earthing leakage path could distort the readings.
Ie - Probes -> Soil -> Earthed power supply -> Power supply ground -> probes
Also are the Individual Plant Pots electrically isolated? - Electrical leakage between them could also distort the readings.
Ie - Probes -> Soil -> Earthed power supply -> Power supply ground -> probes
Also are the Individual Plant Pots electrically isolated? - Electrical leakage between them could also distort the readings.