Can Mars top soil be transformed to be arable, and how to do it?
It may be planted in the isolated space.
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The problems with Mars are:
It is cold. Practically no plant can survive below 0 degrees Celsius. (Some plants can grow below this temperature, and others can survive it and grow if the temperature is over 0 C for some of the year - but there's still a big gap between this and a Martian wheat field.) On Mars, only during the equatorial noons do temperatures $\approx 15 ^\circ C$. The problem could be solved by using greenhouses or genetically modified plants.
There is no oxygen. While plants create oxygen by photosynthesis, they also use oxygen. They don't need too much, though.
There is very little water. Although much water was found recently on Mars, overall Mars is still very dry, like the Sahara desert. It might be possible to mine water ice regularly from the poles and then transport it to the equatorial greenhouses.
Significant radiation from the Sun, mainly UV. This is because Mars has no ozone layer (to defend against UV radiation), and only a very small magnetic field (to defend against protons). Note that a single layer of glass, such as in a greenhouse, would filter out practically all UV radiation.
Perchlorate salts in the soil. They are poisonous for most plants, but making resistant plants is not impossible with genetic engineering. There are known perchlorate-resistant bacteria. Alternatively, the perchlorate ions could be removed from the soil by chemical means.
These problems could all be solved, but none of them would be easy.
Most likely, the first plantations will be in greenhouses and they will utilize mined water, and use processed soil. They will need to operate in closed water and atmosphere loops.
One proposed method for this would be to use silica aerogel: https://www.nature.com/articles/s41550-019-0813-0. This would block UV light and also raise the temperature to above freezing point (via the greenhouse effect). As for the water problem, while there is indeed no liquid water on Mars, there is water chemically bound in minerals like gypsum, which some plants can use: https://www.nature.com/articles/ncomms5660. And there are microbes which can feed on perchlorate: https://science.sciencemag.org/content/340/6128/85. A combination of these methods might be used to make the Martian soil arable.
According to NASA, it is already "almost" arable:
[...] the soil on Mars actually does have the nutrients plants would need to survive on Mars! There may not be the right amount of nutrients depending on where astronauts land on the Red Planet, so fertilizers may need to be added to the soil. The perchlorates in the soil would be leached out and separated from the water [...]
The problem is that it contains perchlorates, which are toxic to humans and plants as well.
However, some plants are resistant to them and may actually help in removing them from the soil.
Other answers mention that you could also remove perchlorate by using bacteria, by chemical means or simply by genetically engineering your plants to be resistant to it (althought if they still absorb it you might not be able to eat them right away).