The determination of moisture content in soils under tension follows the assumption that the water matric potential is at equilibrium with an applied tension. The time the soil water tension reaches the equilibrium under the 6kPa tension was determined in Hapludalf and Hapludox clay soils. In the Hapludalf, the equilibrium between the applied tension and water matric potential, in most of the samples, was obtained between 72 and 96h, while in Hapludox, equilibrium was not reached until the 168h. The water tension in the samples had no significant correlation with bulk density and did not reach the tension applied on the suction table and sand suction column. Nevertheless, more than 97% of the soil water was extracted at 48h both in Hapludalf and Hapludox, suggesting that this time is sufficient to estimate the soil moisture at 6kPa tension, independently of clay content.
water retention; hydrostatic equilibrium; bulk density
