How can I get soil for my Martians?

Question

We've created a series of mechanisms to terraform the temperature and atmosphere to be Earthlike. My geologists are screaming at me, because a lot of features are being rapidly eroded by the new hydrological process. Anywho.

I still don't have soil.

Our agronomists are great with hydroponics, but to plant small trees and root-based plants, I need real soil. Soil formation takes time and organic processes. A lot of both; neither of which I have. And while we really scored with the atmospheric science, we haven't progressed past 2015 for 'creating soil;' how can I get the massive amounts of needed soil?

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Note 1: I read the book, The Martian, where he makes soil for potatoes from poop and Martian regolith. I was skeptical, and a friend who worked at the National Resources Conservation Service (specifically with soil survey), said, "That simply can not happen; that much soil would take forever to become viable." And a lot more than just poop*.

Note 2: I was admonished (down-voted) for stressing the importance of soil previously, so my question is not whether we need it; it's how do we get it.

Note 3: *- I look forward to the day that poop gets its own tag, since I've seen it in WB frequently. [ Done. —ed. ]

Answer 1

There is a good treatment in The Martian, where he uses his own night soil and composting all organic waste. With geometric growth it will cover "land" in short order, given water and labor to spread, mix, and prepare. (Weir's characters all refer to all dead regolith/crushed rock as "soil" too, which bugs me).

Heinlein's Farmer in the Sky describes the work of doing that on a holmstead-sized scale.

What's your friend have against it? It might be just fine in a closed planting box. It also doesn't need to be self-sufficient as an ecosystem, just allow the plant roots to work. Plants can be grown hydroponicly, so a large planter is possible.

In general, you want to carefully prepare both the microbiome and other self-replicating agents that extract power and resources in situ while doing the task of mixing and spreading further. E.g. earthworms, grubs, and various bugs.

Given crushed mineral matrix as a pre-existing starting point, you need to add water and inoculate the biome. If optimally mixed/layered/tended it will double in a few days, and you can divide that and repeat.

Using plots larger than you can tend explicitly, you want a small, patch to grow outward, which will be less efficient moving from soil to plain rock and only along the border which is growing linearly not geometrically.

So you improve it two ways: transplant into new disjoint patches as much as you can, and somehow coax it to spread in a fractal pattern. RAH's farmers made stripes which grew together. How about controlling the irrigation to lead the growth in a pattern? Also engineer the "bugs" to cause dispersion to new areas.

Back to your friend's objections regarding the time scale and input. First, you are a well-prepared mission not a castaway with nothing but his own poop and one living plant. You can have a complex mix, multiple different mixes for different stages, and even engineered species.

The difference between "big pot" and "self-regulating ecosystem" is not all or nothing. For good story, you can imagine managing the degree of hands-on regulation needed vs. the size that can be handled with available labor and logistics.

Amending the soil while plowing and planting, adding fertilizer to irrigation, and weeding and checking pests, is all normal in agriculture which is more productive than nature. If you can add stuff— nutrients or new bacteria and fungi— to the irrigation water, you can easily give it whatever it needs on a day-to-day basis. So maybe you don't need anything more than crushed stone, essentially doing hydroponics on the ground.

Answer 2

This actually sounds like two unrelated questions: How do I stop erosion?, and, how do I transition from hydroponic agriculture to soil based agriculture?

For a fast means of providing ground cover, I might suggest that the ecological engineers start tweaking bacteria to create a strain (or strains) which form biofilms which cover the landscape. As a bonus, the bacteria start the process of terraforming soil and provides a source of nutrients for the next "generation" of ground cover. As noted in JDługosz answer, the cover should be spread in a fractal or checkerboard pattern to maximize coverage and infill.

For feeding a growing population, hydroponics and related techniques provide a compact and reliable means of providing food for the colony. Since we are living in a closed ecology, diverting poop to reconstitute soil outside of the colony is actually not a viable course of action. the waste materials will need to be processed to recycle the nutrients and water back into the system.

This also means the growing population will need to be mining the Martian crust (and possibly asteroids and Jovian moons) for minerals and trace elements to increase the capacity of the system. Some of the materials will also be diverted to the Martian surface to build the soil (although the timescale on this may be a millennium).

So the Martians will be spreading their bacteria on the soil for a millennial soil building project, while keeping their internal economy internal to provide food and oxygen to the colony. Even the external vegetation for the successive phases of terraforming will be "imports" in order to keep the closed cycle life support systems viable.

Answer 3

Mars already has dust fields.

Add water to the dust and you get mud.

Add seeds to the mud and you get plants.

Wait for a year and you get dead plants.

Spray the fields of dead plants with the right bacteria and they will decompose back into the dust and you will have soil.

repeat this process for a few years and then it will become self sustaining. The soil will gradually get deeper and richer like earth.

Plants grow in mars dust: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0103138

Select carefully the most suitable Earthplants, or even genetically engeneer them to increase the effectiveness of this plan.

But then, if plants grow in mars dust, why did you want soil?

Answer 4

Your friends objection is irrelevant. We are teraforming a planet with near future technology. "Quick" is not in our mission statement. So go back to your friend and ask what he means by "forever". If this is shorter than "we need more waste than 200 years of hydroponics would generate", there is simply no concern. It will take a long time, but we are in a slow process.

Your geologists objections is a bit weird. Almost certainly any plant growth and athmosphere will start in protected environments. There should be minimal impact beyond our walls. By the time we are able to start moving plants outside, we will have decades of growth of plant matter that we allow to decay to form our soil. Also, we are terraforming Mars with near future tech, keeping any landmarks recognizable is probably not in our mission profile.

Rapidly terraforming Mars, ie. within a generation or so, does not seem achievable with near future technology. Soil is a problem, but my guess is that athmosphere is a greater problem. Deeper into the future we would probably be able to create soil rapidly from a combination of genetically altered plants that grow hydroponically and nanobots.

Edit: I see that you specify that we get athmosphere "for free". In which case, yes soil production is a real problem. However, in respect to your linked answer, bringing soil from earth remains a poor solution, it's just too expensive to transport that much mass.