Regolith simulant and green compost as substrates for plant cultivation in Mars space colonies

Human exploration beyond Low Earth Orbit will require specific technologies to regenerate resources and exploit the in-situ resources. Higher plants represent an optimal tool for water purification, air regeneration, waste recycling and fresh food supply. However, the configuration of a fertile substrate for plant cultivation based on extraterrestrial soil still represents a challenge in space research. Potato (Solanum tuberosum L.) is a candidate crop for cultivation in Space. We evaluated the plant adaptability to greenhouse cultivation in pots on different substrates, including the Mojave Mars Simulant MMS-1. The simulant alone and in mixture with a green compost 70: 30, v:v, were compared to a fluvial sand, alone or with compost at the same rate, and two terrestrial soils, a red sub-alkaline clay soil, with a high iron content and cation exchange capacity, and a volcanic sub-alkaline sandy-loam soil, with a non-negligible content of carbonates. The leaf area and dry matter accumulation were higher in volcanic soil and on both the mineral substrates amended with green compost, while they were reduced on regolith simulant alone. Plants from pre-sprouted tuber seeds of potato 'Colomba' were grown in pots in a cold greenhouse, completed the tuber-to-tuber cycle and produced healthy tubers on all the tested substrates. Mars regolith simulant alone was revealed to be poor in nutrients and unsuitable for sustaining adequate plant growth without the amendment with composted organic wastes, which changed its physiochemical properties, enhancing fertility.