5.1.18 (HL)—Soil formation factors

Soil formation reflects parent material, climate, organisms, relief and time acting together.

Climate controls weathering and leaching; organisms add and transform organic matter; relief changes drainage, erosion and deposition; parent material supplies minerals and influences pH; and time allows horizons and chemistry to develop. These controls interact rather than acting independently.

Calcareous parent rock rich in calcium carbonate tends to form alkaline soil that may have low organic matter, nitrogen and phosphorus. Volcanic material can weather to release minerals such as magnesium and potassium, often supporting fertile young soils.

Parent material does not determine soil alone: climate, organisms, slope, drainage and time modify weathering, inputs and losses.

No single factor ‘determines’ soil; identify the interacting controls and the process each changes.