Mars Exchange
Food for Mars: Pig Slurry As Manure

Food for Mars: Pig Slurry As Manure

by Natasha Schön on Friday, 3rd November 2017 in Food for Mars

In our latest experiment with the earthworms, some of the pots received a large helping of pig slurry. The slurry is manure for the plants, not for the worms. We use it instead of human feces, and should have a direct effect on the growth of the rucola (rocket). But is it working, and why did we choose pig slurry?

On Mars (or the moon) everything that has the potential for re-use or recycling represents an important resource - and that includes human feces. Indeed, one of the reasons for having a closed agricultural ecosystem is because the natural resources on Mars are scarce and it is hard to utilise them, even in the case of sand and ice. This calls for a closed sustainable agricultural ecosystem. Human feces will therefore have to be used as manure and given back to the plants - as already demonstrated by Mark Watney in 'The Martian'. However, at least for now, we are using pig slurry for the first time as a realistic substitute.

The future use of human feces is not without risks. For instance, it contains all kinds of bacteria which are perfectly safe for us when they occur in the human gut but, when directly applied in manure, they may cause diseases when they come into contact with our body or when entering our bodies. Therefore, it first has to be sterilised before it is used. Not an easy task on Mars, with ‘air’ temperatures up to -100 degrees celcius and deadly cosmic radiation. Though sterilisation is also doable on earth, it is easier to use pig slurry as a substitute and it is also easier to obtain, especially in The Netherlands with all the pig farms. Pig slurry is a good substitute for human feces, since the diet of both is quite similar and the internal organs of the body are comparable and may even be interchangeable.

Now that the worm experiment is well underway, the addition of pig slurry has clearly has its effects. As expected, growth is much stronger in the pots that received the treatment. However, we did not sterilize the pig slurry before application and it quickly became very clear that this was a mistake. Within two weeks we had fungi and even mushrooms growing in some of the pots! The mushrooms were removed, but it clearly showed that pig slurry contains much more than just manure. A second pit-fall was that the slurry also attracted lots of tiny little flies. Something that would never happen on Mars, but something we have to deal with here on earth. The flies were treated with biological pest control to keep their numbers as low as possible. Meanwhile the worms were unaffected and kept doing their job, digging more tunnels and making small piles of sand and manure in the pots.

Do not forget to support the worms if you can!

Story contributed by Wieger Wamelink, a Senior Ecologist at Alterra (Twitter: Wamelink_wieger).

More Information:

Rucola (rocket) on Earth control (bottom) and Mars soil simulant (top). From left to right, manure (pig slurry) and worm addition, manure addition (pig slurry), worm addition and no additions. All pots received organic matter from the previous experiment.

Worm on Mars soil simulant.

Worm excrements between the rucola plants (the light grey sprinkle like forms).

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