MEANS TO INCREASE EFFICIENCY OF ARTIFICIAL SOIL USED FOR ROOT CROPS CULTIVATION IN A SPACE GREENHOUSE

Abstract

The most promising method of root supply in space greenhouses (SG) operating in microgravity is porous membranes together with a capillary-porous salt-saturated artificial soil (AS). AS is a critical consumable that cannot be recycled in space missions. One of the options for increasing the specific harvest of cultures with extended period of commercial vegetation, carrot as an example, can co-cropping with fast-growing greens at the beginning of cultivation. Purpose of this work is experimental testing a technology of co-cropping carrot and leaf vegetables to see whether it will and better the AS efficiency. In a series of 3 experiments carrots were cultivated under a lighting unit with red and white LEDs (PFD in the range of 300 to 600 µmol(m2•s) in root modules stuffed with granular or fiber AS. Co-cultures were lettuce, Japanese turnip and basil. It was demonstrated that PFD at 450 – 550 µmol(m2•s) and water potential in the root zone at [(–0.5) – (–0.8) kPa] are favorable to the carrot and lie within the ranges recommended for cultivation of leaf vegetables in space greenhouses. No negative allelopathic effect was noted during carrot co-cropping with lettuce or Japanese turnip. Carrot cultivation with the Japanese turnip saved the specific, per a crop biomass unit, energy expenditure for lighting. Co-cropping with the Japanese turnip reduced the specific AS expenditure about 4 times; co-cropping with the lettuce reduced AS expenditure in 2.5 times.