Thermistor Hygrometer for determining the Free Energy of Moisture in Unsaturated Soils

IN any investigation involving the movement of moisturo through soils, the measurement of the free energy or total potential of the soil moisture still remains one of the chief problems. The basic requirement of any satisfactory technique for such measurement is that it should depend on some property which is uniquely related to the free energy of the soil moisture and is in no way affected by the soil type. One such property is the relative vapour pressure or humidity in equilibrium with the soil moisture as given by equation (1), where h = free energy (cm water); R = universal gas constant; T = abs. temp.; M = molecular wt. of water; g = 981 cm/sec 2 ; p / p 0 = relative humidity.