Theory question 206
Soils(a) What is soil?
(b) Explain the process of soil formation
(c) Describe a typical soil profile
Show the model answer
(a) The thin, loose upper layer of the earth's surface made of weathered rock particles, humus, water, air and organisms, in which plants grow
(b) Weathering of parent rock (physical, chemical, biological) produces fragments; plants and animals add organic matter which decays to humus; leaching and eluviation move materials down; illuviation deposits them below; horizons develop over a long time; controlled by parent rock, climate, relief, organisms and time
(c) A horizon (topsoil) – dark, humus-rich, loose, many organisms, leached; B horizon (subsoil) – zone of accumulation of clay and iron, compact, little humus; C horizon – partly weathered parent material; bedrock below; organic litter (O layer) on the surface
Name the five soil-forming factors.