is that even an issue? all we need for soil on mars is people, various kinds of aquaponics, and worms, any waste food going to the worms and the liquids made from the worm farm being used to feed the plants, once we have soil, microbes, worms(and a whole host of other microbes, some visible nematodes too) we can grow food easily, id even bring chickens to the party too, they will control the worm population and help to cycle the nutrients around the system the whole process would naturally build soil as a waste product, you could also culture specific microbes from earth that would be useful and bring them to mars to act like bioreactors, some microbe or another can brake down just about anything and if we are going to really live there rather than just be a earth fed colony we will need to ensure we have a good stock of microbes for total self sufficiency you would need a bioreactor that brakes down rocks in to plant soluble form, feed that to large pools of alega, or duck weed and feed that to the animals, eventually you would need to tunnel out some place for a few herds of animals, trees, all that jaz, im kind of surprised that they are not doing this stuff already because its easily doable with our current technology, maybe they are doing it just not telling us about it