Theory question 207
Soils(a) Outline four components of soil. (b) Describe, using a diagram, the soil profile. (c) Highlight any three farming practices that can lead to soil erosion.
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(a) Mineral matter (rock particles); organic matter (humus); water; air; living organisms (micro-organisms, worms).
(b) Diagram of horizons: O/litter layer of dead leaves; A horizon (topsoil) dark, rich in humus, zone of leaching (eluviation); B horizon (subsoil) zone of accumulation (illuviation) of leached minerals and clay, lighter in colour; C horizon of weathered parent rock; D/R horizon of unweathered bedrock.
(c) Bush burning; overgrazing; continuous cropping without fallow; ploughing up and down slopes; clearing all vegetation (deforestation); shifting cultivation with short fallow.
Label each horizon with its letter and a short description.