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C.L. Mackowiak, R.M. Wheeler, G.W. Stutte, N.C. Yorio, and L.M. Ruffe

Peanut (Arachis hypogaea L.) plants were grown hydroponically, using continuously recirculating nutrient solution. Two culture tray designs were tested; one tray design used only nutrient solution, while the other used a sphagnum-filled pod development compartment just beneath the cover and above the nutrient solution. Both trays were fitted with slotted covers to allow developing gynophores to reach the root zone. Peanut seed yields averaged 350 g·m-2 dry mass, regardless of tray design, suggesting that substrate is not required for hydroponic peanut production.

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G.W. Stutte, C.L. Mackowiak, N.C. Yorio, R.M. Wheeler, and L.M. Ruffe

An experiment was conducted in the Biomass Production Chamber (BPC) at Kennedy Space Center to determine the feasibility of continuous steady-state production of potato (Solanum tuberosum L.). Plants were grown in a “batch” or continuous production mode using either 0.5 × modified Hoaglands or effluent from aerobically processed inedible potato biomass as a nutrient source. EC and pH were controlled to 0.12 S·m–1 and 5.8, respectively. The batch harvest occurred after 104 days and continuous harvest occurred every 26 days, with replanting occurring in the same solution. Continuous production on “aged” solution resulted in earlier tuber initiation, reduced plant height, and smaller canopies than the “batch” treatment. Planting density of the continuous treatment was increased from eight to 16 plants/m2. Because one quarter of the planting area was harvested and replanted every 26 days, a steady-state of canopy coverage between 60% to 75% of the chamber was maintained. Steady-state of CO2 fixation was also maintained in the continuous treatment. There was no effect on either quantum efficiency, tuber yield, or harvest index of the plants grown in continuous production. Although replanting into “aged” nutrient solution resulted in earlier tuber initiation and reduced plant size, the system reached a steady state of production, which is desirable for advanced life support system.

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R.M. Wheeler, C.L. Mackowiak, N.C. Yorio, L.M. Ruffe, and G.W. Stutte

Radish (Raphanus sativus cv. Giant White Globe) and lettuce (Lactuca sativa cv. Waldmann's Green) plants were grown for 25 days in growth chambers at 23 °C, ≈300 μmol·m-2·s-1 PPF, and 18/6 photoperiod, and four CO2 concentrations: 400, 1000, 5000, and 10,000 μmol·mol-1. Average total dry mass (g/plant) at the 400, 1000, 5000 and 10,000 μmol·mol-1 treatments were 6.4, 7.2, 5.9, and 5.0 for radish and 4.2, 6.2, 6.6, and 4.0 for lettuce. Each species showed an expected increase in yield as CO2 was elevated from 400 to 1000 μmol·mol-1, but super-elevating the CO2 to 10,000 μmol·mol-1 resulted in suboptimal growth. In addition, many radish leaves showed necrotic lesions at 10,000 μmol·mol-1 by 17 days and at 5000 μmol·mol-1 by 20 days. These results are consistent with preliminary tests in which radish cvs. Cherry Belle, Giant White Globe, and Early Scarlet Globe were grown for 16 days at 400, 1000, 5000, and 10,000 μmol·mol-1. In that study, `Giant White Globe' produced the greatest total dry mass at 1000 (3.0 g/plant) and 5000 μmol·mol-1 (3.0 g/plant), and the least at 10,000 μmol·mol-1 (2.2 g/plant). `Early Scarlet Globe' followed a similar trend, but `Cherry Belle' showed little difference among CO2 treatments. Results suggest that super-elevated CO2 can depress growth of some species, and that sensitivities can vary among genotypes.

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R.M. Wheeler, G.W. Stutte, C.L. Mackowiak, N.C. Yorio, and L.M. Ruffe

Potatoes (Solanum tuberosum L.) have been grown successfully with a recirculating nutrient film technique (NFT) when a fresh nutrient solution is used for each planting. During the past year, we conducted two studies in which the same nutrient solution was used for successive plantings (EC and pH were maintained at 0.12 S·m–1 and 5.8). Results showed that successive plantings became prematurely induced (tubers initiating near 20 days after planting–DAP), causing stunted shoot growth and reduced yields per plant. When “old” nutrient solution from a continuous production system was regularly added to a newly started plant system maintained under a non-inductive environment (12-h photoperiod with night break of 6 h into dark), tubers formed on “old” nutrient solution plants (24 DAP), but not on “new” solution plants. When charcoal water filters were placed on the systems, plants grown on either “old” or “new” nutrient solutions showed no tuber initiation (plants harvested at 42 DAP). Results suggest that a tuber-inducing factor(s) emanating from the plants accumulates in the nutrient solution over time and that the factor(s) can be removed by charcoal absorption.