On Mar/3/2021 at 09:19, David Spain wrote :
IMHO one of the biggest blows to the concept was went it was discovered
that the chemical composition of Martian soil sampled at one of the
lander sites (I forget which) showed that the soil contains poisonous
compounds that would either prevent plant growth or cause grown plants
to become inedible. Therefore either soils will have to be transported
from Earth or food grown hydroponically. I suppose one could hold up
hope that with an extensive surface exploration program, maybe one might
find a spot on Mars that is otherwise. Seems unlikely from where we
stand today.

I'm not sure what you're talking about up there with the chemical
composition of Martian soil. I've heard that the soil is too salty. If
you have a cite for some information I don't have please provide it.
Soil that is too salty isn't a show stopper, just a hassle.

Here is how you would start a greenhouse operation on Mars. First you
plant a few rugged plant, let's call them weeds, that can survive in
harsh conditions. If the soil is really too difficult for plants, you
can bring from Earth a little soil to start; you mix that Earth soil
with some Martian soil. Once your weeds have grown, you cut them and put
them in the compost pile (really a bio-digester instead of a compost
pile, you don't want to wait years for your compost). Your weeds have
extracted some nutrients from the Martian soil, so you can get more
fertile soil from your compost than what you brought from Earth. The
nutrient depleted Martian soil can be discarded. You start again with
another batch of Martian soil. Because you had more fertile soil to mix
with Martian soil than the first time, you can harvest more weeds than
the first time. Repeat... Once you have enough compost you can start
growing tomatoes or what not. You still continue to grow weeds because
you want to increase your amount of fertile soil in order to increase
the produce crop sizes. For a fixed amount of produce you shouldn't have
to add new soil from the weeds, the nutrients for the next generations
of produce can come from the compost from the unused parts of the plants
and the ... ugh ... manure the colonist make.


Alain Fournier