A little while ago, I told you about a preliminary experiment that Dr Wieger Wamelink and his team at the University of Wageningen conducted. It demonstrated that it is possible to grow plants in simulated Mars and Moon soils.
The next step in their research was an experiment focusing on ten crop species. Their goal was to produce edible crops and some viable seeds. A major difference to the first experiment was that they added some organic matter to the simulated soils as if they had ‘ploughed in’ the crop residues from the first experiment. They used freshly mown grass as the organic matter; Lolium perenne (perennial ryegrass) is a common meadow grass species in the Netherlands.
The ten crop species chosen were:
- Tomato ‘Supersweet 100 F1’ (Solanum lycopersicum)
- Rye ‘Summer Rye’ (Secale cereale)
- Garden cress ‘Broad Leaved’ (Lepidium sativum)
- Leek ‘Farinato’ (Allium ampeloprasum)
- Quinoa (Chenopodium quinoa)
- Pea ‘Prince Albert’ (Pisum sativum)
- Radish ‘Bel Image’ (Raphanus raphanistrum subsp. sativus)
- Spinach ‘Prickly Seeded’ (Spinacia oleracea)
- Rocket ‘rucola’ or wild rocket (Diplotaxis tenuifolia)
- Chives ‘Garlic Taste’ (Allium tuberosum)
“Species were selected to provide a representative selection of crops with different edible parts, except for below ground parts (roots, tuber etc.). Leek, radish, rocket and chives were also selected because of their spicy taste. Astronauts on the ISS often complain about the taste of their food and spicy crops may therefore be a welcome addition to their diet.”
The team sowed their seeds on 9 April 2015, in a greenhouse in the Netherlands, in Mars simulant JSC Mars-1A and Moon simulant JSC-1A. (Organic potting soil was used as the Earth ‘control’ soil.) They fed each tray of plants once a month with a balanced liquid fertiliser. This was to mimic inputs that could be made from astronauts urine and faeces! They watered each tray daily.
The researchers cared for their plants this way for 159 days until the experiment ended on 5 September 2015. They then harvested, dried and weighed all of the top growth of the plants.
The only crop that didn’t grow well on any of the soils was spinach, which promptly bolted (formed flowers rather than leafy growth). The harvest included radishes and radish seeds, cress and cress seeds, rye seeds, rocket, tomatoes and peas. Chives and leeks grew slowly in all three soils. The quinoa grew well and flowered, but did not set seed.
The highest weight of plants was harvested from the Earth soil, but the Mars simulant wasn’t far behind. There was less plant growth in the Moon simulant, which may be because it has a higher pH.
Producing seed crops will be a necessary part of long-duration space missions and self-sustaining off-world settlements. The team ran a germination experiment in April 2016, testing the rye, cress and radish seeds they had collected. The rye seeds germinated well on all three soils. Germination of cress seeds was also good, although slightly lowers on the simulated soils. Radish seeds showed the lowest germination, dropping to around 50% on the simulants.
This was the first experiment to grow plants to seed on Moon and Mars simulants. It showed that adding organic matter to the simulants improves plant growth (something that will be of no surprise to organic gardeners!). More research is needed to determine the optimum amount of organic matter required for crop growth. The team also want to investigate: recycling organic matter with worms and bacteria (space composting!), using nitrogen-fixing bacteria and symbiotic fungi to reduce the need for fertiliser, and recycling human wastes into plant nutrients. They’ve already started work on some of those, and I’ll delve into that soon.
“We were thrilled when we saw the first tomatoes ever grown on Mars soil simulant turning red. It meant that the next step towards a sustainable closed agricultural ecosystem had been taken “.Wieger Wamelink
Wamelink, G. W. W., et al. “Crop growth and viability of seeds on Mars and Moon soil simulants.” Open Agriculture 4.1 (2019): 509-516. DOI:10.1515/opag-2019-0051.