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Nov 02 2015

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I was wondering this as I was watching “The Martian”, too

Farming on Mars? The Martian raises questions about soil. Spoiler Alert! The movie is still showing in theaters, so SPOILER ALERT!!

Astronaut Mark Watney grows a small garden of potatoes to help feed him after he’s become a castaway. He moves Martian dirt inside his habitat, burns rocket fuel to produce water to wet the soil, and adds his own freeze-dried poop to the dirt (after he mixes it into a slurry with water) for fertilizer. This is definitely an experiment I’d like to try sometime (yes, even using my own poop), because I have my doubts that Watney could have gotten this to work.

This is not to take away from the movie in any way — it’s still one of the best Space/Science movies ever, and if you haven’t seen it yet, what in the world are you waiting for?

Anyway, my doubts involved the dirt. It is completely sterile when he begins to use it, whereas Earth soil (even terrible soil like we have here in SoCal) is an ecosystem teaming with microbes that help circulate nutrients through the soil and are necessary to helping plants grow.

Here are the two hypotheses that I’d be exploring in my garage-based Martian garden test:

  1. Is straight human poop too “hot” to grow plants? Usually, poop is composted before it can be used for fertilizer, as (I think) the nitrogen it uses to decompose is sucked away from the plants’ roots, causing the plant to die. I had this problem a couple of years ago when I tried to use our horses’ manure as a soil additive for our garden. Even after composting it and letting it sit for 6 months, it was still too hot for my garden and nothing grew. Wouldn’t the same thing happen if you put straight human poop into ground?
  2. Assuming plants aren’t killed by Hypothesis 1, then are there enough nutrients in Martian dirt to allow microbes from the human poop to grow throughout the sample to turn the dirt into usable soil? “Usable” being defined as able to sustain multiple iterations of crops (as in the movie). Of course, after the first crop, a lot of the plant waste could go back into the soil, which may help it become sustainable.

Watney was a botanist, so presumably he knew a lot of tricks to start up the soil and keep it healthy. Indeed, in the book he did more than what was shown in the movie:

In the book, Watney took other steps, such as fertilizing and amending soil, which were not included in the movie. “You can only include so much information in a movie lasting a little over two hours,” says Bell.

He also had nothing but time on his hands (er…besides dirt and poop), so the soil would definitely have gotten a lot of TLC.

Permanent link to this article: http://www.newspaceraces.com/2015/11/02/i-was-wondering-this-as-i-was-watching-the-martian-too/

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