soil horizon layers. o is humus or organic, a is topsoil, b is subsoil, c is parent material and r is bedrock.

soil garden plant grass lawn yard tree green flower wall wildlife shrub leaf backyard rock geology agriculture asphalt woodland nature root forest wood roots branch sand dry ground brown trunk trees old environment soils three major horizons surface horizon subsoil substratum organic buried master used subsurface loss minerals eluviation layers topsoil parent material bedrock