Soil

Soil is a natural, dynamic medium that forms the interface between the lithosphere and the biosphere. It consists of mineral grains, organic matter, water, air, and a diverse soil biota. Soils vary in texture, structure, chemistry, and moisture, yet all support plant growth and play key roles in water regulation and nutrient cycling.

Soil develops through weathering of parent material under the influence of climate, organisms, relief, and time. This process creates horizons, typically O, A, E, B, C, and R, though not all soils have every layer. The O horizon contains litter, the A horizon mineral soil mixed with organic matter, and the B horizon accumulates clays and oxides.

Soil texture describes the relative amounts of sand, silt, and clay and affects drainage, aeration, and nutrient availability. Structure and porosity influence root growth and water retention. Chemical properties such as pH, cation exchange capacity, and base saturation govern nutrient availability and metal mobility.

Soil biology includes roots, fungi, bacteria, nematodes, and invertebrates that drive decomposition and nutrient cycling. Soils store carbon and water, filter contaminants, and provide habitat for numerous organisms. They support agriculture, forestry, and ecosystem services and, in some contexts, influence construction and archaeology.

Poor management can lead to erosion, compaction, salinization, pollution, and loss of organic matter. Sustainable practices—crop rotation, cover crops, reduced tillage, organic amendments, and proper drainage—help conserve soil structure, fertility, and biodiversity and sustain productivity over time.