A Horizon

A surface mineral layer. It will typically have humus mixed within the soil, have good biological activity, especially earthworm activity, being a good environment for micro-organism activity helping to decompose organic matter within this soil profile. This horizon is also typically relatively fertile, usually having a good range of available plant nutrients. The soil will often be fairly well drained, although still be able to retain adequate amounts of available water for plant use. An 'A' Horizon is typically darkish in appearance and is commonly referred to as topsoil.