Martian Agriculture

The idea of agriculture on Mars is interesting. Need to check a few basic plants, like algae, lichens, soy beans, corn, and wheat. The idea would be to try different combinations of compressed Martian air and water vapor. Or maybe just air, and let the water come from that which you feed to the roots. One would also have to reduce the intensity of the input solar radiation to be a Mars equivalent.

Note that temperature is also an issue. All the components are low-tech, but if we don't do the research it will be alot harder to get started with the food supply there. (One possibility is to fund the research, and the other is to do it myself).

It's almost like a science fair project. One question is how dangerous is CO2 at these concentrations. As long as one keeps the containers small, there shouldn't be a problem. If one had an entire greenhouse, though, it might be a little dangerous. On the other hand, you could probably rig up an interesting breathing apparatus.

When you think about it, there should be some real basic data out there about lighting and nutrient sensitivity for plant growth for wheat, corn, and soybeans. You'd think. If grown in hydroponic conditions, given normal moisture and root nutrients, what is the light curve? Ok, given reasonable lighting and nutrients, what is the moisture curve? Etc. Maybe 2d or 3d maps.

Ignoring crops for a moment and just looking at any plant, one can ask what is the moisture loss. Is it feasible to have plants naked on the surface, or do you need to have other ways of retaining the moisture? Also, what about ultraviolet radiation? Chances are that having plants under glass is the winning way to go, both for UV protection and moisture retention.

Chris Rode writes: 4) I'm 100% certain plants on the naked surface of Mars is an impractical idea, even if you shield them from the UV. You'll definitely want a greenhouse. Aside from the cold, water is precious and plants respire water like crazy. However, I would only be slightly surprised if you could find some plants that can actually grow at low Mars-atmospheric pressures, as long as the PP of CO2 is high (which it is, of course). < 1% of the Earth's atmosphere is CO2 and if you had a 1% pressure atmosphere of 100% CO2 with unlimited access to water, some plants might grow under those conditions. Now, how you fertilize them with nitrogen is another matter. Will nitrogen fixing bacteria work in an atmosphere that's 95% CO2 and 4% N2? You don't want to haul Miracle Gro up from Earth!

Good point about the nitrogen. Since there's a little in the atmosphere, the main gas processing you might want to do for agriculture may be obtaining the N2 out of the air (liquify compressed Martian air, followed by a little Haber-Bosch?). Certainly finding deposits of ancient martian bat guano would be helpful. ;-)

This issue of PP of CO2 and plant growth is significant. Do our plants really need all this thick neutral gas (N80% O20%) that they swim in, or can one just have the CO2 and be done with it?

Zubrin has a couple of paragraphs on this in his Case for Mars, and claims that 50 mbars with a certain mix of gases will work, but I need to hunt down his references.

You're right, though, that one of the big things will be how dry the martian air is. Freeze drying is done with a vacuum for a reason. Need to be very strict about how water tight the green house is.

I wonder whether one could set up a backyard Biosphere II experiment with a sealed atmosphere and water cycle. Probably run afoul of the Dept of Agriculture or the State Board of something or rather.

One point is that Mars green houses may need lungs, just like Biosphere II has. It won't be as extreme as BS2, but something has to be done about the variation in pressure. Or not. Guess it depends on how much pressure the green house is at.

Note: 10 mbar = 1 kPa = 0.14 psi

It's worth quoting here from Zubrin's Case for Mars:
Mars atmosphere, on the other hand, is sufficiently dense to protect crops grown on the surface against solar flares. On Mars, as we have seen, large inflatable greenhouses protected by geodesic comes could be readily deployed, rapidly creating huge temperate-environment domains for crop growth. Martian sunlight levels, at 43 percent those of Earth, are entirely adequate for photosynthesis, which in fact could be accelerated relative to Earth by filling the domes with higher concentrations of carbon dioxide than are available on Earth. We have seen that a 1-mm thick Kevlar reinforced dome fabric would be needed to support a 50-meter diameter habitation pressurized to 5 psi (340 mbars). However plants require only 0.7 psi, or 50 mbar of atmospheric pressure with 20 mbar nitrogen, 20 mbar oxygen, 6 mbar water vapor, and less than 1 mbar of carbon dioxide comprising the atmosphere. A fabrix only 0.2-mm thick would be sufficient for a 50-meter done if it were used as a greenhouse only. Such a dome, enclosing about 2,000 square meters (a half acre) of crop land, would have a fabric mass of about one tonne, but its Plexiglass shield mass would still be 4 tonnes.

using such low-pressure domes would force those inside to wear spacesuits. Raising the dome pressure to 2.5 psi would eliminate the need for spacesuits.

p. 195, The Case for Mars, Zubrin & Wagner, 1996.

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