Root restriction: A tool for improving volume utilization efficiency in bioregenerative life-support systems

The objective of this study was to evaluate root restriction as a tool to increase volume utilization efficiency in spaceflight crop production systems. Bell pepper plants (Capsicum annuum cv. California Wonder) were grown under restricted rooting volume conditions in controlled environment chambers. The rooting volume was restricted to 500 ml and 60 ml in a preliminary trial, and 1500 ml (large), 500 ml (medium), and 250 ml (small) for a full fruiting trial. To reduce the possible confounding effects of water and nutrient restrictions, care was taken to ensure an even and consistent soil moisture throughout the study, with plants being watered/fertilized several times daily with a low concentration soluble fertilizer solution. Root restriction resulted in a general reduction in biomass production, height, leaf area, and transpiration rate; however, the fruit production was not significantly reduced in the root restricted plants under the employed environmental and horticultural conditions. There was a 21% reduction in total height and a 23% reduction in overall crown diameter between the large and small pot size in the fruiting study. Data from the fruiting trial were used to estimate potential volume utilization efficiency improvements for edible biomass in a fixed production volume. For fixed lighting and rooting hardware situations, the majority of improvement from root restriction was in the reduction of canopy area per plant, while height reductions could also improve volume utilization efficiency in high stacked or vertical agricultural systems.