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Regenerable Seed Plugs from Formed Plant Fiber.    R.C. Morrow, C.J. Ehle and T.M. Crabb.  Orbital Technologies Corporation, 1212 Fourier Dr, Madison WI.

A project was undertaken to develop techniques for producing seed plugs from formed plant fibers for Advanced Life Support (ALS) plant growing units. Plant plugs can place a significant impact on an ALS if they cannot be completely recycled. For example, an annual supply of seed-starting structures such as seed plugs would be on the order of 150 to 5000 kg for a six-person base, depending on the seeding technique used. The primary challenge was to develop regenerable plant supports that retain structural integrity in a wet, humid environment for one crop cycle, can be easily fabricated on-site, are non-toxic to plants, and do not require separation from the inedible plant waste stream. To produce plant plugs, wheat fiber was processed using a combination of dry and wet refining and then formed into mats using pulp-molding techniques.  After testing fiber size combinations, fiber mats were formed into plant plugs for use in structural and biocompatability tests. A variety of molds, both for “plug” and “linear wedge” configurations were also fabricated and tested in the pulp molding system. Tests conducted on the plant plugs included tensile (tear) strength testing, a four week plant growth study using lettuce and comparing growth to that obtained with commercially available inorganic plant plugs, and a germination study using a variety of crop plants. Plant tests showed that some of the wheat-based plugs showed a reduction in plant growth. However, wedge shaped linear plugs from wheat showed plant productivity equivalent to commercial plugs.  Plugs fabricated from wheat fiber did release organic materials that could support microbial growth into the nutrient solution. However there was no indication of toxic materials being released. Leaching of the wheat fiber with hot water during the wet refining process removed significant amounts of organic carbon and inorganic nutrients. However, it appears that an additional leaching step is probably required. Germination tests showed that wheat plugs supported germination at about the same rate as commercial plugs. Plugs fabricated from coarse cut wheat fiber showed distinctly better plant development than did the plugs fabricated from fine cut wheat fiber.