... light-grayish, moderately-loamy, cultivated forest soil.
I have one objection to this: I would lose the hyphen between
moderately and
loamy. But I know that hyphens are more popular in British English than in American English.
Some more comments:
I think I would just say either
light gray (in which case I'd also lose the hyphen) or
grayish.
Light-grayish strikes me as too much gray-modifying, but if you need that degree of precision then by all means go with it.
This may have been obvious to you, Panj, but I'll explain it for the benefit of the greater WRF population. It is true that when we have a list of adjectives preceding a noun, we do not place a comma between the last adjective and the noun. But note that in this case there is no comma between
cultivated and
forest, either. That's because
forest is so closely attached to
soil that the two form a unit that could be treated as a single noun for punctuation purposes. We may as well spell it
forest-soil or
forestsoil.
More examples:
a beautiful, expansive, state-of-the-art auditorium
but
a stately, well-maintained grand piano (no comma between
well-maintained and
grand)