The evaluation of soil water content in the vadose zone, through the determination of the water limits is possible with a newly developed methodology: water activity meters. Its principle of operation, based on the Kelvin equation provides a dependency on two factors, temperature and relative humidity. This research quantifies the effect of both in determining the permanent wilting point in soils of Galicia. We have analyzed 26 sites with a model WP4 activity meter. In 16 samples were quantified an increase in temperature, according to the percentage of moisture, 0.92% (5%) 1.28% (10%), 1.79% (15%) and 1.76% (20 %), with an average of 1.44%. In the remaining 10 samples is a decrease in relative humidity of the samples throughout the protocol with respect to the initial values of 42.84% (5%) 47.83% (10%) 50.65% (15%) and 53.42% (20%), with an average decrease in the process of 48.68%. Extrapolated the permanent wilting point, is related to the amplitude of the variation in temperature and relative humidity for each sample. The average variation was 0.315 cm3cm-3 ºC-1 and 0.003 cm3cm-3 in the wilting point for each unit change in the relative humidity. Highlighting the near relationship between the temperature-humidity and the time required, recommended a larger survey of the boundary conditions, questioning the use of such equipment in field conditions.
