Wednesday, November 15, 2006 - 1:15 PM

Porous-Media Water Retention and Distribution Observed in Variable Gravity during Parabolic Flight.

Robert Heinse and Scott Jones. Utah State University, Ag. Sci. Bldg. Room 160, Logan, UT 84322-4820

Water retention and the distribution of water in reduced gravity remains a key area of study for future plant growth experiments in space that utilize coarse-textured porous media. While impressive advances have been made in reduced gravity plant research, the sample scale behavior of water in the root zone remains ambiguous. Part of the problem stems from the limited availability of long-term reduced gravity experiments. Building on past experience, our objectives were to utilize the limited period of near-zero gravity during parabolic flight to (1) measure water retention in coarse-textured porous media and (2) determine the transient response of water distribution for unsaturated conditions. For these experiments, we constructed two novel test cells. The water retention cells were 11 mm tall shallow-sample cells intended to minimize the hydrostatic effect on the hydraulic potential within the sample. Minimizing this effect is crucial because of the intermediate periods exhibiting nearly twice earth’s gravity, which significantly impacts the distribution of water in the sample. In contrast, the cell for determining the unsaturated distribution of water was 7 cm tall. The goal was to monitor the distribution and redistribution of water as gravity alternates between near zero and twice earth’s gravity. For this we added five sets of horizontally-oriented 4-electrode arrays for measuring the electrical conductivity, with each set spaced 1-cm apart. The electrical conductivity was used to sense changes in the vertical distribution of water as a result of changes in gravity regime. Fast responding pressure transducer-tensiometers were used in both test cells to determine the hydraulic potential. Results and observations are projected to foster our understanding of reduced gravity effects on sample-scale porous-media hydraulic properties.