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containment and liquid and gas phase separation in microgravity by using microporous membranes to control Hydroponic culture has traditionally been used for controlled enviwater delivery to plants. In the present configuration ronment life support systems (CELSS) because the optimal environment for roots supports high growth rates. Recent developments in of this method, nutrient solution flows under a slight zeoponic substrate and microporous tube irrigation (ZPT) also offer negative pressure through microporous tubes and is dehigh control of the root environment. This study compared the effect livered by capillary action directly to roots (Dreschel of differences in water and nutrient status of ZPT or hydroponic and Sager, 1989) or to solid substrate (Morrow et al., culture on growth and yield of wheat (Triticum aestivum L. cv. USU-1994; Tibbitts et al., 1995). A nearly constant matric Apogee). In a side-by-side test in a controlled environment, wheat potential can be maintained in solid substrate by conwas grown in ZPT and recirculating hydroponics to maturity. Water trolling water flow and pressure through microporous use by plants grown in both culture systems peaked at 15 to 20 L m Ϫ2 tubes. The dynamics of water transport through a microd Ϫ1 up to Day 40, after which it declined more rapidly for plants grown porous tube-solid substrate-plant system was studied in ZPT culture due to earlier senescence of leaves. No consistent by Steinberg and Henninger (1997), who showed that differences in water status were noted between plants grown in the two culture systems. Although yield was similar, harvest index was water holding and transport characteristics of solid sub-28% lower for plants grown in ZPT than in hydroponic culture. Sterile strate determine the range of viable operating pressures green tillers made up 12 and 0% of the biomass of plants grown in of the system. ZPT and hydroponic culture, respectively. Differences in biomass Little is known about the growth and yield of plants partitioning were attributed primarily to NH 4 -N nutrition of plants grown in solid substrate maintained at a nearly constant grown in ZPT compared with NO 3 -N in hydroponic nutrient solution.matric potential by microporous tube irrigation as com-It is probable that NH 4 -N-induced Ca deficiency produced excess pared to hydroponic culture. Cao and Tibbitts (1996) tillering and lower harvest index for plants grown in ZPT culture. compared biomass production and gas exchange of po-These results suggest that further refinements in zeoponic substrate tato (Solanum tuberosum L.) grown in a microporous would make ZPT culture a viable alternative for achieving high protube irrigation system containing isolite (a porous ceductivity in a CELSS.

Hydroponic culture has traditionally been used for controlled environment life support systems (CELSS) because the optimal environment for roots supports high growth rates. Recent developments in zeoponic substrate and microporous tube irrigation (ZPT) also offer high control of the root environment. This study compared the effect of differences in water and nutrient status of ZPT or hydroponic culture on growth and yield of wheat (Triticum aestivum L. cv. USU-Apogee). In a side-by-side test in a controlled environment, wheat was grown in ZPT and recirculating hydroponics to maturity. Water use by plants grown in both culture systems peaked at 15 to 20 L m-2 d-1 up to Day 40, after which it declined more rapidly for plants grown in ZPT culture due to earlier senescence of leaves. No consistent differences in water status were noted between plants grown in the two culture systems. Although yield was similar, harvest index was 28% lower for plants grown in ZPT than in hydroponic culture. Sterile green tillers made up 12 and 0% of the biomass of plants grown in ZPT and hydroponic culture, respectively. Differences in biomass partitioning were attributed primarily to NH4-N nutrition of plants grown in ZPT compared with NO3-N in hydroponic nutrient solution. It is probable that NH4-N-induced Ca deficiency produced excess tillering and lower harvest index for plants grown in ZPT culture. These results suggest that further refinements in zeoponic substrate would make ZPT culture a viable alternative for achieving high productivity in a CELSS.

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