Document Type

Unpublished Paper

Publisher

Utah State University

Publication Date

12-2025

First Page

1

Last Page

11

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

Abstract

Flexible containment materials are essential for repeated planting cycles in the Utah Reusable Root Module (URRM), a zero-discharge system developed for space-based crop production. In previous trials, a vinyl top cover provided effective evaporative control and media retention but could not meet flight certification. To identify a suitable alternative, this study evaluated food-safe, flight-qualifiable silicone rubber sheets as an impermeable top cover for a wedge-based seeding system. The silicone rubber was tested at three thicknesses (1/32", 2/32", and 3/32") in combination with three linear fringe lengths (1.0", 1.5", and 2.0") and two fringe widths (0.25" and 0.5") and compared with an uncovered control. Mizuna (Brassica rapa var. nipposinica) was grown in peat-based media in greenhouse trays irrigated daily to maintain target volumetric water content (θv ≈ 0.60 cm³ cm⁻³), estimated by weighing.

Seedling emergence, early-stage growth, fresh biomass accumulation, cumulative evapotranspiration (ET), ET rate, and the post-harvest condition of the silicone covers were quantified. All treatments supported high seedling emergence (83–95%), with slightly lower values in the 3/32" thickness but no statistically significant differences across treatments. Fringe geometry had no significant effect on mean emergence, though the 1.5" length and 0.25" width combination achieved 100% emergence across thicknesses. Fresh biomass per tray was highest in the uncovered control and moderately reduced under silicone covers, reflecting a trade-off between containment and biomass accumulation.

Silicone covers reduced water loss by approximately a factor of four during the early evaporation-dominated phase, while ET converged among treatments as transpiration dominated later in the growth cycle. After 29 days, the silicone fringes remained intact, and mold was only observed in the uncovered treatment. Overall, food-safe silicone rubber with linear fringes is a promising reusable top-cover design, enabling replanting and high emergence while substantially reducing early evaporation and mold risk in compact, flight-qualifiable root modules.

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