Space agriculture: Effects of low gravity on water flow, nitrogen cycling, and microbial biomass dynamics in a soil-based cropping unit

In the hypothesis that Mars can be inhabited by a six-people crew by 2050, bioregenerative agriculture has being considered as a mean to recycle water, produce food, sequester CO2, produce O2, and decompose organic wastes. However, Mars gravitational acceleration (0.38g) has unknown consequences on most physical and biogeochemical processes within the root zone, where adequate supply of water, nutrients and O2 is required by plants and microorganisms. On Mars, gravitational advection would be substantially different than on Earth, but it is not clear whether this would hinder, maintain or facilitate nutrient accessibility. As pore wetting in reduced gravity would be more likely to nucleate air pockets, the unsaturated hydraulic conductivity would be much lower, and air pockets could entrap gases (e.g., O2) and dissolved nutrients (e.g., NH4+ and NO3ˉ), not available to roots and microorganisms at the rates they would on Earth.

We investigate the feedback that low gravity has on water flow, and its effects on the soil-nutrient-biomass dynamics in a soil-based agricultural plot on Mars using a mechanistic soil reactive transport model. We demonstrated that under a 0.38g Martian gravity, leaching of water, N and C decrease by 50-70% as compared to Earth, but emissions of N2O, N2 and CO2 gases increase respectively by 150%, 350%, and 20% relative to Earth. Martian soil-based agriculture would require 50-70% less irrigation water volume, and about 50% less net N supply (e.g., fertilizers) as compared to on Earth. Ideally, low water and nutrient footprint would make soil-based cropping an attractive option to support life on Mars. (Collaboration with F. Maggi, Sydney University)