Additional green light would make the plant leaves appear green and normal, similar to a natural setting under white light, and may also offer psychological benefits for the crew. The combination of red and blue LEDs has proven to be an effective lighting source for several crops, yet the appearance of plants under red and blue lighting is purplish gray, making visual assessment of plant health difficult. Among the lighting technologies considered for space are light-emitting diodes (LEDs). Current lighting research for space-based plant culture is focused on innovative lighting technologies that demonstrate high electrical efficiency and reduced mass and volume. These lamps vary in terms of spectral quality, which can result in differences in plant growth and morphology. Several types of electric lamps have been tested to provide radiant energy for plants in this regard, including fluorescent, high-pressure sodium, and metal halide lamps. Hence, a hydroponic nutrient solution N management system may be modified to elicit greater plant N-use while maintaining overall high tuber yield as opposed to achieving high tuber yields through excess N supply and shoot growth.Abstract: The provision of sufficient light is a fundamental requirement to support long-term plant growth in space. However, proportionately more plant accumulated N was used (N use efficiency) to produce tuber biomass when N supply was abruptly lowered at tuber initiation in Expt. II, less N was taken up and accumulated by plants compared to those which received high constant N (control). By abruptly decreasing N supply at tuber initiation in Expt. II), plants were able to achieve yields on par with plants which received constant 7.5 mM NO3(-)-N (control). When supplied with an external 7.5 mM NO3(-)-N for the first 42 days after planting (DAP), lowered to 1.0 mM NO3(-)-N during the final 42 days (Expt. III) did not significantly benefit tuber yield, but did influence N use efficiency indices. I), or disabling pH control, and/or supplying NH4(+)-N (Expt. Treatments which decreased NO3(-)-N supply indirectly through lowering nutrient solution EC (Expt. In separate 84-day cropping experiments, three N management protocols were tested. Hence, the primary objective of this study was to identify the optimal N management regime and plant N requirement to achieve high yields and to avoid inefficient use of N and excess inedible biomass production. More effective strategies of N fertilization need to be developed to more closely match N supply with demand of the crop. Furthermore, the high amount of N used in NFT-hydroponics, typically results in high inedible biomass, which conflicts with the need to minimize system mass, volume, and expenditure of resources for long-duration missions. Although tuber yields have been excellent with such an approach, N use efficiency indices are expected to be low relative to tuber biomass production. Standard nutrient solution management approaches include constant pH regulation with nitric acid (HNO3) and daily adjustment of electrical conductivity (EC) equivalent to half-strength modified Hoagland's solution, where nitrate (NO3-) is the sole nitrogen (N) source. The National Aeronautics and Space Administration (NASA) has been conducting controlled environment research with potatoes (Solanum tuberosum L.) in recirculating nutrient film technique (NFT)-hydroponic systems as a human life support component during long-duration spaceflight.
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