CHANGES IN THE MATRIC POTENTIAL OF SOIL-WATER WITH TIME AFTER DISTURBANCE OF SOIL BY MOLDING

Moulding of moist soil samples destroys most of any pre-existing structure and results in a spatial homogenization of the distribution of three component phases: mineral particles, water and air. Such an arrangement is not entirely stable and, if such a disturbed system is allowed to rest, structural rearrangements occur so as to minimize the free energy of the system. Samples of six soils from Australia, The Netherlands and the U.S.A. were moulded at a range of water contents and kept at constant water content in sealed plastic cylinders. Matric water potential was measured with tensiometers, which required only a small water exchange to give an equilibrium reading. Structural rearrangements in these soil samples produced more-negative values of water potential with time over the 30-day period after moulding. Some of the soils exhibited two distinct stages of change of water potential with time. There was no clear correlation between the observed behaviour and soil composition. However, the temperature dependence of the tensiometer readings was proportional to the clay content of the soil samples. © 1990.