Soils and Natural Zones
Soil formation
Soil forms from parent material acted on by climate, organisms, relief and time. A soil profile has horizons (O, A, B, C, R). Key properties are texture (sand, silt, clay), structure, colour, pH, humus content and drainage. Leaching removes soluble material downward; podzolisation occurs in cool, wet coniferous zones; laterisation occurs in hot, wet tropics; salinisation occurs in dry, irrigated areas.
Soil types and natural zones
Know the pairing of climate, vegetation, soil and zone: tundra (permafrost, thin soils), taiga (podzols), temperate forest (brown forest soils), steppe (chernozem, rich in humus), desert (thin, saline, stony), Mediterranean (terra rossa on limestone), savanna and tropical rainforest (leached, acidic). Chernozem is a classic exam favourite because of its fertility.
Human influence
Erosion, overgrazing, deforestation, monoculture and pollution degrade soils; terracing, crop rotation, contour ploughing and organic matter restore them. Soil conservation links physical geography to agriculture.
Traps
Don't assume tropical soils are fertile because vegetation is lush; don't confuse leaching (removal) with salinisation (accumulation of salts); and remember that humus content, not colour alone, drives fertility.
Rule of thumb
Match the zone to its climate: wet and cool gives podzols, dry grassland gives chernozem, hot and wet gives leached tropical soils, and dry irrigated areas risk salinisation.