Modeling gravity effects on water retention and gas transport characteristics in plant growth substrates

Abstract

Growing plants to facilitate life in outer space, for example on the International Space Station (ISS) or at planned deep-space human outposts on the Moon or Mars, has received much attention with regard to NASA's advanced life support system research. With the objective of in situ resource utilization to conserve energy and to limit transport costs, native materials mined on Moon or Mars are of primary interest for plant growth media in a future outpost, while terrestrial porous substrates with optimal growth media characteristics will be useful for onboard plant growth during space missions. Due to limited experimental opportunities and prohibitive costs, liquid and gas behavior in porous substrates under reduced gravity conditions has been less studied and hence remains poorly understood. Based on ground-based measurements, this study

The Water‐Induced Linear Reduction Gas Diffusivity Model Extended to Three Pore Regions

“…The 3WLR model characterization is also shown for each soil together with the corresponding model parameters. Data from (a) Freijer (1994), (b) Chamindu Deepagoda et al (2011, 2014), and (c) Grable and Siemer (1968).…”

“…Weakly aggregated mineral and organic soils: Three Dutch soil data sets from mineral (Belvedere C) and organic (Speuld O moder and Speuld O mor) soil profiles (Freijer, 1994), Chinampas (Spanish) soil data from a top organic layer (0–7 cm) (Ikkonen et al, 2012), and differently compacted Chernozem Rendzina (Polish soil) from a humus‐rich horizon (Stepniewski, 1980). Well‐aggregated porous media: Hayden soil data, which include five different particle fractions and a mixture thereof (called “soil”) (Grable and Siemer, 1968), a micro‐aggregated Japanese (Nishi‐Tokyo) Andisol (Chamindu Deepagoda et al, 2011), and a particulated porous medium “profile” (0.25–0.85 mm) proposed as a prospective plant growth substrate for Earth‐ and space‐based applications (Blonquist et al, 2006; Chamindu Deepagoda et al, 2012, 2014). Fractured porous media: fractured plastic (Gradwell, 1961) and seven Danish (Aalborg) soils sampled from a fractured limestone profile (Kristensen et al, 2010).…”

The Potential for Lunar and Martian Regolith Simulants to Sustain Plant Growth: A Multidisciplinary Overview

“…Although reduced gravity can influence gas and fluid movement, it does not necessarily lead to better rhizospheric conditions. This is because the root zone is primarily influenced by air in pore spaces (Chamindu Deepagoda et al, 2014). Therefore, if the small pore space is filled with air and the substrate is almost watersaturated, conditions could become critical for plant growth and would need to be managed carefully.…”

Microgravity Oxygen Diffusion and Water Retention Measurements in Unsaturated Porous Media aboard the International Space Station

“…Given that estimates for α varied significantly between the Flat and Round cell estimates, definitive conclusions cannot be drawn based on the available observations without further verification. Results do, however, suggest that the air‐entry value (inverse of α) does not scale with the gravitational force, as suggested by Jones et al (2005) and used by Chamindu Deepagoda et al (2014). For drying conditions, no significant differences were noted for estimates of α in the three media, with significant differences in the estimates for the parameter n for Mix and Profile.…”

“…The authors predicted that relative diffusion coefficients may be reduced by up to 25% in zero gravity based on lattice Boltzmann simulations. In another modeling effort, Chamindu Deepagoda et al (2014) predicted an increase in gas‐percolation threshold with a reduction in gravity on the basis of gravity scaling of the air‐entry value in the water retention characteristic. However, no experiment has directly measured water retention or oxygen diffusion in sustained long‐term microgravity.…”