Soils

Soils are the unconsolidated mineral and organic matter that cover much of the land surface. They form by weathering of bedrock and by accumulation of organic material from plants and animals. A soil comprises minerals, organic matter, water, and air, and supports diverse life. Soils develop distinct horizons, commonly labeled O, A, E, B, C, and R, though not all soils exhibit every layer.

Formation is controlled by climate, organisms, relief, parent material, and time, often summarized as CLORPT. Key properties include texture (sand, silt, and clay), structure, porosity, color, pH, and fertility. Soils support plant growth by storing and supplying water and nutrients, provide habitat for organisms, regulate water flow, and sequester carbon.

Classification systems vary; most describe soils by texture and horizons and by diagnostic features to assign orders. The USDA Soil Taxonomy and the FAO/WRB system are widely used. Soils range from sandy to clayey, acidic to alkaline, and fertile to nutrient-poor.

Human activities degrade soils through erosion, compaction, salinization, and contamination. Sustainable management includes erosion control, maintaining organic matter, crop rotation, appropriate tillage, drainage, and pollution prevention. Restoration may involve revegetation, terracing, and soil amendments.

Soils underpin food production, water quality, climate regulation through carbon storage, biodiversity, and cultural values. Protecting soil health requires integrated land management and monitoring of properties. Although diverse, soils share the role of mediating terrestrial ecosystems.