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Measurement of Hydraulic Characteristics of Porous Media Used to Grow Plants in Microgravity
Author(s) -
Steinberg Susan L.,
Poritz Darwin
Publication year - 2005
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2005.0301
Subject(s) - porous medium , hydraulic conductivity , porosity , saturation (graph theory) , particle (ecology) , materials science , characterisation of pore space in soil , soil science , mechanics , environmental science , geology , mathematics , soil water , composite material , physics , oceanography , combinatorics
Understanding the effect of gravity on hydraulic properties of plant growth medium is essential for growing plants in space. The suitability of existing models to simulate hydraulic properties of porous medium is uncertain due to limited understanding of fundamental mechanisms controlling water and air transport in microgravity. The objective of this research was to characterize saturated and unsaturated hydraulic conductivity ( K ) of two particle‐size distributions of baked ceramic aggregate using direct measurement techniques compatible with microgravity. Steady state (Method A) and instantaneous profile measurement (Method B) methods for K were used in a single experimental unit with horizontal flow through thin sections of porous medium providing an earth‐based analog to microgravity. Comparison between methods was conducted using a crossover experimental design compatible with limited resources of space flight. Satiated (natural saturation) K ranged from 0.09 to 0.12 cm s −1 and 0.5 to >1 cm s −1 for 0.25‐ to 1‐ and 1‐ to 2‐mm media, respectively. The K at the interaggregate/intraaggregate transition was ≈10 −4 cm s −1 for both particle‐size distributions. Significant differences in log 10 K due to method and porous medium were less than one order of magnitude and were attributed to variability in air entrapment. The van Genuchten/Mualem parametric models provided an adequate prediction of K of the interaggregate pore space, using residual water content for that pore space. The instantaneous profile method covers the range of water contents relevant to plant growth using fewer resources than Method A, all advantages for space flight where mass, volume, and astronaut time are limited.