Early seedling response of six candidate crop species to increasing levels of blue light.

Light emitting diode (LED) lighting technology for crop production is advancing at a rapid pace, both in terms of the technology itself (e.g., spectral composition and efficiency), and the research that the technological advances have enabled. The application of LED technology for crop production was first explored as a tool for improving the safety and reliability of plant-based bioregenerative life-support systems for long duration human space exploration. Developing and optimizing the lighting environment (spectral quality and quantity) for bioregenerative life-support applications and other controlled environment plant production applications, such as microgreens and sprout production, continues to be an active area of research and LED technology development. This study examines the influence of monochromatic and dichromatic red and blue light on the early development of six food crop species; Cucumis sativa, Solanum lycopersicum, Glycine max, Raphanus sativus, Pisum sativum, and Capsicum annum. Results support previous findings that light responses are often species specific. The results also support the assertion that monochromatic light can interfere with the normal interaction of various photoreceptors (co-action disruption) resulting in intermediate and sometimes unpredictable responses to a given light environment. The nature of the responses reported inform both bioregenerative life-support designs as well as light quality selection for the production of controlled environment crops.

Light-emitting diodes as an illumination source for plants: a review of research at Kennedy Space Center.

The provision of sufficient light is a fundamental requirement to support long-term plant growth in space. 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. These lamps vary in terms of spectral quality, which can result in differences in plant growth and morphology. Current lighting research for space-based plant culture is focused on innovative lighting technologies that demonstrate high electrical efficiency and reduced mass and volume. Among the lighting technologies considered for space are light-emitting diodes (LEDs). 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. 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 addition of 24% green light (500-600 nm) to red and blue LEDs enhanced the growth of lettuce plants compared with plants grown under cool white fluorescent lamps. Coincidentally, these plants grown under additional green light would have the additional aesthetic appeal of a green appearance.

Influence of nitrogen nutrition management on biomass partitioning and nitrogen use efficiency indices in hydroponically grown potato.

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. 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. Although tuber yields have been excellent with such an approach, N use efficiency indices are expected to be low relative to tuber biomass production. 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. More effective strategies of N fertilization need to be developed to more closely match N supply with demand of the crop. 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. In separate 84-day cropping experiments, three N management protocols were tested. Treatments which decreased NO3(-)-N supply indirectly through lowering nutrient solution EC (Expt. I), or disabling pH control, and/or supplying NH4(+)-N (Expt. III) did not significantly benefit tuber yield, but did influence N use efficiency indices. 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. II), plants were able to achieve yields on par with plants which received constant 7.5 mM NO3(-)-N (control). By abruptly decreasing N supply at tuber initiation in Expt. II, less N was taken up and accumulated by plants compared to those which received high constant N (control). 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. 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.