Optimized Light Quality and Fertilizer Composition for Crop Production on the International Space Station

Producing fresh food will be essential in order to supply optimal nutrition for astronauts at distant space destinations. Efficient practices for sustainable production of leafy greens in space are currently being studied on the International Space Station (ISS). Providing adequate light quality, quantity, and fertilizer formulations will be a significant challenge for production of salad crops in space. The ISS currently houses the “Veggie,” a small, modular, light emitting diode (LED)-based plant-growth unit developed by the Orbital Technologies Corporation (ORBITEC). Veggie analogs (VAs) have been developed by ORBITEC and are being utilized for ground-based testing in growth chambers at both the Kennedy Space Center and at Purdue University to mimic the carbon dioxide, humidity, and temperature environments of the ISS. These VA units include an LED light cap and a passive irrigation system that allows plants grown at 1xg to be compared with those grown in microgravity. Studies demonstrate that the use of red + blue LEDs can provide sufficient quality and quantity of photosynthetically active radiation, whereas incorporating green LEDs creates deeper plant-canopy light penetration and aesthetic appeal as plants appear greener. Optimized spectral composition and fertilizer ratios for crop species down-selected by NASA have yet to be determined. In this study, Chinese Cabbage (Brassica rapa cv. Tokyo Bekana) was grown for 28 days in a soilless medium consisting of 75% arcillite (calcined clay) + 25% vermiculite using 100 or 180 day slow-release, polymer-coated 18-6-8 N-P-K fertilizer in three different ratios: 100% 180, 66% 180 + 34% 100, and 50% 180 + 50% 100. Four different light-quality treatments were analyzed with three different ratios of red and blue light: 82% R + 9% B, 64% R + 27% B, 45.5% R + 45.5% B, and one split treatment using 82R:9B for 21 days and 45.5R:45.5B for the remaining 7 days. All treatments were supplemented 9% green light with a combined total PPF of 330µmol/m²/s when measured from the central point of the growth area. A passive irrigation system replenished transpiration water losses from a wicking reservoir. Plants grown under more red-dominant light exhibited more biomass accumulation than other treatments. Light quality had a stronger impact on plant growth and development than did fertilizer quality. Jointly funded by the Human Research Program and Space Biology in the ILSRA 2015 NRA call under grant NNX15AN78G.