A Brief Survey about Farming on Mars

In conjunction with the excitement around the Mars 2020 rover Perseverance, which will launch this summer and arrive on Mars next February, I bought 1 kilo of Martian soil simulant which I’ll try to do a few experiments with in my farming and gardening. With limited time and a lack of certain controls, I probably won’t be able to do much hard science, but I hope to have fun seeing how crops may do in the simulant. Time to fess up- one of my hobbies is staying up on current space exploration and issues surrounding that. Exobiology, exolinguistics, and farming across the solar system, those are some of the sub-topics I like to think about.
Anyways, the simulant I got, from https://sciences.ucf.edu/class/exolithlab/ , is specifically based on spectral analysis of the site the Perseverance rover is aiming for, Jezero Crater. Technically, soils of other planets is called regolith, since it’s presumably not full of forms of life, organic matter, and other things we may mean when we say soil, but for my purposes I find the distinction unhelpful. I’ve seen plenty of Terran soil overworked and devoid of life, I didn’t switch to calling it regolith then, did I? And I hope and expect that we’ll have Martian soil teeming with life soon anyway.
I hope to make a page with a compendium of helpful links on sites and articles that discuss farming on Mars, as I’ve amassed a list in the course of reading on it.

The first question for the economics oriented people, is why on Earth would you grow crops in a difficult location like Mars versus an easy place like Earth. The simple truth is that Martian-grown crops are only a smart long-term investment- not a short-term. Most space exploration math comes down to the fuel needed to move a given mass. Shipping seeds to Mars, and letting Martian sunlight, water, and soil make food, is eventually going to make more sense than relying on Terran food. Earth's gravity is relatively strong, and there is a huge embodied cost to every kilogram that needs to leave it.

Secondly, a next-step consideration is that Mars will be a far more effective "bread basket" and low-to-mid tech manufacturing hub for humanity exploring the asteroid belt and beyond- for several simple reasons. Its soil is farmable (shown in this Dutch study), its gravity is 38% of Earth's (making every shipment that much cheaper to launch), and its day-night cycle is very close to Earth's, allowing most of our growing knowledge on Earth to apply there. Though it would force humans to wear a breathing apparatus, we can also get away with just pressurizing native Martian atmosphere, with minor amounts of supplemented oxygen, for a CO2 rich environment that could help make up for the weaker sunlight. So...while Martian crops are currently expensive and R-and-D-heavy, they will soon be the affordable option for support logistics for the Belt.
It should be useful to note that Mars’ day is 24 hours and 40 minutes long, while its year is roughly double ours. It also has an axial tilt that’s very close to our tilt, giving seasons that are similar to ours in their relative variation from each other- though Mars’ thin atmosphere and distance from the sun mean that all seasons are colder than Terran equivalents, of course. It also means that your latitude on Mars will result in roughly similar climate equivalents- equatorial regions, tropical regions, temperate regions, et cetera.  Based on lots of reading, between the negative effect of its distance from the sun, partially mitigated by its super thin atmosphere (0.6% of Earth’s pressure), Mars receives about 50% the solarization of Earth, at least for solar panel design purposes. Not being an engineer, I’ve wondered if the math for solar panels would be terribly different for plants- is it basically like a 50% shade cloth? We farmers can buy various percent-rating shade cloths to moderate our greenhouse’s solarization, I wonder if it’s that simple. Some plants chug along fine in partial shade. The opening of leaf stomata to move nutrients (via water) from roots to leaves is determined by a tri-partite plus combination of sunlight striking the leaf and creating super-low humidity conditions near the leaf surface, the ambient atmosphere itself (pressures affecting boiling/off-gassing points, temperature being a description of the speed with which that can happen). Long story short, while a couple things work against us (the strength of the sunlight), other factors make it more likely we can mitigate it- thinner atmosphere, higher CO2 enrichment, etc.
I share that brief overview because basically, assuming we are able to build greenhouses out of plastic or glass, there’s a long list of reasons that our Terran farming skillsets will work on Mars. Most of the plants we’ve bred to succeed on Earth will have it in their genetic code to work on Mars. Many vegetables rely on day length signals to set seed, senesce, or switch to storage mode, and due to the nearly same length of day and axial tilt, a given latitude on Mars will correspond fairly close to that same latitude on Earth- only difference is that the total growing season will be twice as long but with 50% solarization- you’ve got twice the time to grow it, but every day will be partly cloudy. Cultivars that grow better in low light conditions- such as many vegetables bred for the extreme latitudes or the Atlantic coasts, will be the most likely to succeed.
The biggest issue is that real Martian soil is full of perchlorates, which are molecules that rapidly oxidize anything they come in contact with- bad for organic matter. The simplest way to get rid of perchlorates is to leach your soil of them using water- this means that every cubic foot of Martian soil will need to be saturated to the point of total leaching before it can be used to grow things. Since I believe the engineers will be, a la Zubrin, cranking out methane and water in a Sabatier reaction, water will soon be an abundant resource, a byproduct of propellant production, so washing soil, while tedious, will be quite doable. Since we have to focus on all in situ resources, I think that complicated hydroponic systems are just not bootstrap enough- we’ll have to be old-school in making soil work for us. With careful composting of all waste, and good ole cover crops, the Martian soil will quickly come on line for us as a resource.
*Post Script on perchlorates- there is a company that has isolated bacteria which, with a little help, can biologically break down perchlorates- https://www.microc.com/applications/perchlorate/
I don’t know if their process could be helpful up on Mars but it’s worth knowing about- one more tool in the toolchest!