The sensitive element of the capacitive soil moisture sensor is a humidity sensitive capacitor. And the main materials are generally metal oxides and high molecular polymers. These materials have a strong adsorption capacity for water molecules. And the amount of water absorbed varies with the change of environmental humidity. Because water molecules have a large electric dipole moment, the permittivity of the material changes after water absorption. And the capacitance value of the capacitor also changes. The soil moisture sensor best to detect soil moisture .