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 it, and others can survive it and grow if the temperature is over 0C for a little part of the year - but between this and a Martian wheat field, there is a huge gap.) On Mars, only during the equatorial noons do temperatures $\approx 15 ^\circ C$. The problem can be solved by using glass houses, or by genetically modified plants.
There is no oxygen. While plants create oxygen by photosynthesis, they also use oxygen. They don't need too much.
There is only very little water. Although much water was found recently on Mars, overall Mars is still very dry, like the Sahara. It is possible, that water ice could be regularly mined on the poles, and then it has to be taken to the equatorial glass houses.
Significant radiation from the Sun, mainly UV. It is because Mars has no ozone layer (to defend against UV radiation), and only a very small magnetic field (to defend against protons). Note, a single layer of glass, as used in the windows, filters out practically all UV radiation.
Perchlorate salts in the soil. They are poisoning for most plants, but making the resistant 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 all can be solved, but none of them is easy.
Most likely, the first plantations will be in glass houses and they will utilize mined water, and use processed soil. They will need to operate in closed water and athmosphere loop.
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).