Farming on Mars

Let’s presume the collective world has gotten out of its space-exploration budget-funk, and has decided it’s worth sending people to Mars. The first have gone and have returned, and now it’s time to set up a colony.

Of course that colony will have to be self-sufficient. Thankfully, there are a number of very useful things on Mars, so the colonists won’t need to bring everything, but the more they can find locally, the better. Ideally they should not need anything from elsewhere to survive after an initial supply of resources.

Most importantly, the colonists will have to grow their own food.

At its distance from the Sun, sunlight on Mars is about 40% up to half that on Earth, but still sufficient as power source.

Unless the colonists choose to grow plants in hydroponic systems, they will have to use Martian soil. Preliminary analysis shows that the basic composition of Martian soil is fairly similar to certain soil types on Earth. To be sure, no one has ever taken a sample from Mars and returned it to Earth, but we have two methods for determining composition of Martian soil and/or rocks. In the first place, there are meteorites that have reached Earth from Mars, of which 34 are known. Without going into a lot more detail, they are all igneous rock, in other words, hardened lava. These rocks tell us about the composition of the Martian crust, but very little about sediments, water and free elements in the soil. Secondly, in 2008, the Phoenix lander carried equipment that allowed it to perform an in-situ analysis of the soil near Mars’ north pole. The soil turned out to be alkaline, and contain elements necessary for plant growth, such as sodium, magnesium, potassium and chloride.

However, things are unlikely to be as simple as that. For one, it’s not correct to refer to the substrate as ‘soil’ (but failing a different, similarly evocative word, I will use it anyway), since the definition of soil includes the presence of organic material. The Martian regolith (which is a word I should use instead) contains none. Plants need soil for two basic purposes: for anchoring, and for their nutrition. Plants can anchor themselves in virtually anything (which is why you get plants growing in concrete and on roofs), as long as they have enough water and food. Water is available on Mars in the form of ice. The colonists will be deposited somewhere close to a source of this ice.

But what do you think would happen if you wet a soil that has been dry for billions of years? A soil that has been subject to direct radiation and dust storms. For one, there will be a lot of fine material. On Earth, growing crops in heavy, gluggy soils with lots of fine particles (clays) is hard. Plants need adequate aeration to grow properly. If the soil becomes too compacted (either because it is too fine or because people walk over it) plants don’t grow properly. This is why there is frequently no grass in a soccer goal. So you’ll have to get rid of excess dust before you wet the Martian soil else the stuff will turn into something akin to cement and be of no use for cropping. Also, there will be something like four billions years’ worth of accumulated salts that are freed if you wet this soil. When the Phoenix lander wetted the Martian soil, it released perchlorates, which are poisonous to plants. The soil pH was alkaline (8.3), which indicates accumulated salts of one type or another.

There are plants, notably those that are native to deserts, that tolerate a high salt concentration in the soil, but in order to grow highly-strung and finicky crop species, it’s necessary to get rid of excess salt. This probably requires a lot of (recycled) water, but at the very least, it will require lots of detailed testing, and time.

Next: the air. Mars has lots of carbon dioxide. Plants grow better with a higher concentration of carbon dioxide than present on Earth. It makes sense to run the glasshouses with a high carbon dioxide level. But at high carbon dioxide concentrations, the plants are likely to take up an increased percentage of poisonous elements from the soil, such as arsenic, cadmium and lead. Some areas of Mars are known to have fairly high concentrations of arsenic.

The big trouble is going to be nitrogen, because there is very, very little of that on Mars. Nitrogen is an element that does not easily form bonds with other elements. Whereas oxygen facilitates chemical reactions by reacting with other elements (for example by burning or rusting), atomic nitrogen just does… nothing. Since we have seen in an earlier post that Mars is too small to hold onto its atmospheric nitrogen, there may not be all that much of nitrogen to be found on Mars in any of its forms. So unless early explorers locate a deposit of nitrogen-rich substrates, the colonists will have to import nitrogen from elsewhere. And nitrogen is the most essential of the essential elements for plant growth.

All of which is not suggesting that using Martian soil for cropping is impossible, but that it likely isn’t easy or straightforward, and that early colonists are probably better off starting with hydroponic installations while all this other testing takes place.

Growing crops in space #2

In truth, this post should read ‘Growing crops in artificial environments’, because it applies equally to crops grown in a hypothetical space station as it does to crops grown on the Moon, or Mars or any fictional celestial body.

I’ll start off with a few open doors:
– All crops we grow as food today exist in some form in the wild. In all of those cases, humanity has bred better varieties to the point where the original plant bears no more than a passing resemblance to the crop variety. For example, compare a wild rose with the ones you buy at the florist. It’s hard to believe the commercial rose is directly descended from the wild rose. This has come about by selecting varieties with desirable characteristics (in other words: mutations) and propagating them, selecting the best plants out of that crop, and so on, and so forth. While the selection process is human-driven, there is nothing unnatural about the commercial rose’s DNA.
– All plant species evolved to be suited to their native climate. The banana is a tropical crop and will do poorly when temperatures are too low. Similarly, the banana evolved to grow in a climate where the temperature range is fairly narrow (in other words: where it’s always hot), and where the daylength doesn’t vary much either. Never thought about this? Well, here’s an everyday illustration: I live in Sydney (33 degrees south). I go to the gym at 6.30 most mornings. At that time, the TV in the gym has the news on. It’s summer right now, and at 6.30 it’s pretty light in Sydney. If, however, the news program crosses to someone in Cairns (16 degrees south), you’ll see that it’s still pitch dark over there. If they cross to someone in Hobart (42 degrees south), it has been light down there for ages. These three cities are more or less on the same latitude. In winter, exactly the opposite will happen. It will be light in Cairns, dusk in Sydney, and still pitch dark in Hobart.

To sum up, Cairns has much less annual variation in the length of its day. This is, incidentally, why daylight saving in the tropics is neither sensible nor desirable. Trust me, I lived there. You do not want daylight saving. (/soapbox).

What does this have to do with crops?

Well, you’ll probably have noticed that most crops are highly seasonal. People in our cities don’t notice this so much, because food suppliers use two mechanisms to extend availability: 1. storage (if you buy apples in February, I can guarantee that they’re about year old), 2. different source areas (with its handy dual temperate/tropical climate, Australia can grow temperate crops in winter in the tropics and in summer in the temperate regions. Surprise, surprise, most of our staple vegetables are temperate crops).

But the tropical crops that are highly seasonal (fruit trees—the banana is NOT a tree) are only available in summer. This is why mangoes come onto the market in November and tail off in January.

(for the record: Australia imports almost none of its essential fresh food)

OK, seasonal crops. Bowen mangoes flower in late August, and the fruit is ripe in the first week of November.

Why does the mango tree flower in August? Because, as in animals, plant reproduction is a hormonally-induced process that responds to triggers.

These triggers are:

– Temperature. Many plants need a cold period to flower. If you’re sick of your Phalaenopsis orchids always flowering in May, put them in a cool room at 15C for two weeks, and they’ll flower any time of the year.
– A dormant period. This is especially important in temperate plants. Dormancy is often controlled by temperature, but only because temperature triggers the production of certain plant hormones. Are you a Sydneysider who has lived in Europe? Have you ever noticed how the paltry few European oak trees in Sydney hardly lose their leaves in winter, much less produce acorns? This is why. No loss of leaves = no dormant period = no acorns.
– The real biggie: daylength. Almost all plants will react to changes in daylength by speeding up their maturity, or delaying it. This is what you are doing trying to grow a crop outside its native climate zone. Parsley, a temperate herb, is a natural biannual, but when you grow parsley in the tropics, it will neither flower nor die after two years. Parsley needs a short day (in other words: a temperate winter) to induce flowering.

And now you’re taking this hotchpotch of plants with their varying requirements into space and growing them in a controlled environment. Each species has its own maturity triggers and sensitivities. Some plants (tomatoes) are pretty much insensitive to anything you throw at them. Others (wheat, maize, rice) can be far more fussy. And daylength rhythms can be disturbed by something the strength of a street light at night (ever noticed how oak tree branches surrounding a street light are weeks ahead of the rest of the tree?)

If you want anything approaching the full range of crops you can buy in a regular supermarket, you’d have to make some adaptations to your artificial environment design. You could modify the artificial environment but supplying a few chambers with different conditions, or you could breed plants that are less sensitive to daylength (this sensitivity is controlled by a single gene). In any case, taking everyday Earth crops into space for mass food production will require a lot of thought. That, or your characters will get mightily sick of eating tomatoes.

So you want to be a space farmer?

You are writing space-based Science Fiction, and have decided your world is going to have a self-sufficient space station, base or space ship. A lot of Science Fiction books have this assumption in common. Any human colony, whether on a moving vessel, space station or on the surface of a planet, will need to produce its own food, since vast distances and transportation costs will make import unpractical. Being self-sufficient means growing stuff to eat. Here are a few points to consider to make your food production system more realistic.

There is a fair bit written about the design of the habitat. It ideally needs to be in the habitable zone of a star or closer to make optimal use of light. Artificial light is expensive and mineable energy is scarce in the depths of space. If you do position a habitat far from a star, make allowances for vast amounts of energy needed to grow plants. Without cheap and easy solar energy, the energy source would probably have to be nuclear and would have to be shipped in.

Other requirements run parallel with those for human habitation. The habitat needs to have radiation shielding. It needs to have adequate air circulation, temperature control and day-night cycles.

(ETA: this interesting article was published a week or so after I wrote this post. It deals with the effect of radiation on crops and how it seems plants can evolve to deal with it)

As an agricultural scientist, I often get annoyed when SF books suggest that ‘magic happens’ inside a food-producing habitat. You just chuck in the necessary elements, wave your fingers and POOF, there is food on the table.

In reality, things are lot more tricky than that. Once you add a biological element to your controlled environment, the system becomes complex and liable to unexpected and sudden failure.

The nutritional needs for plant growth are simple enough, but since you’re in space, you’ll have to cart everything in. Plants need the following to grow: Main elements: C, H, O. Main nutritional elements: N, P, K. Also essential: S, Ca, Fe, Mg, Mo, Mn, B, Cl, Zn and Cu. A lot can be recycled, but you’ll need to replenish occasionally.

One of the lessons learned from the Biosphere 2 experiment is that maintaining a viable ecosystem in a closed environment is damn hard. Biosphere 2 was a mixed ecosystem, containing many species. An agricultural centre aboard a facility in space is more likely to contain a much smaller range of species, making it much more vulnerable. For example, the grass family (maize, wheat, rice), the nightshade family (potato, tomato, capsicum, egg plant), the cabbage family and the cucumber family (pumpkin, cucumbers) provide a huge chunk of our daily vegetable needs. A virus only need take out one of those families and you have a severe problem.

Closed ecosystems are extremely vulnerable to pests & diseases resulting from less-than-optimal air circulation and light conditions. When something goes bad, it does so in spectacular fashion, quickly and without easy remedy. I’ve seen this happen several times… in glasshouses… on Earth.

For that reason, you’ll want backups. Don’t rely on one system, or one crop, or one station.

There will have to be some artificial tofu-like foodstuff produced for easy protein and nutritional value. Most plants are extremely wasteful in their useful crop/waste ratio. Compost works very well on a farm in the open air, but in a space station, it just…. stinks.

A process of rigorous, dare I say neurotic, quarantine will be necessary. You cannot risk anyone bringing in the tiniest mite or aphid from outside.

Some crops and livestock are much more suited to high production per unit area than others. Use tropical crops with a fast cropping cycle (C4 crops such as rice and corn) over temperate crops. Breed varieties of crops which can efficiently utilise a higher-than-usual CO2 percentage. Plants grow bigger in low-gravity conditions, and use more water.

There are some crops you won’t be able to grow no matter what. They’re either too expensive to grow or for some mysterious reason defy all attempts at growing them in any sort of health or quantity in a controlled environment. You can’t always explain why this happens. Biology is funny like that. Of course, those crops will be the most valued.

Where are you going to get your initial seed-stock and how are you going to conduct breeding and renewal? I could see a situation where each growing condition requires a different type of plant. The more variety, the less risk of wipe-out due to disease.

To sum up, a food production scheme needs to be reliable and robust. Diversity is the key to risk-spreading. My guess is you’ll probably end up having to resort to some quick & dirty chemical shortcuts, such as mining O2 from comets to make sure you have the capacity to quickly act in case of impending ecosystem collapse due to disease.