Topsoil contains organic matter (humus)
Tundra.
The Fertile soil contains lots of microorganisms which decompose the complex dead bodies of animals and plants into simpler substance called Humus.
topsoil.
topsoil
humus
topsoil
b horizon
All soil contains some humus. If it doesn't it is not soil.
marshy swampy biome
podzolic do not have much fertile humus. this causes a bright brown colour.
Probably the ocean biome, but the rain forest biome on land would have the highest species diversity.