soil fertility; soil quality; productivity of the soil
「地味」 has another reading with different meanings.
plain; simple; subdued; sober
彼女は地味な服装を好むんだ。
She prefers plain clothes.
地味だけど大切な仕事だと思う。
I think it's plain but important work.
派手より地味なほうが好きだな。
I prefer plain over flashy.