1 Soil Formation and Soil-Forming Factors
Learn how weathering and five interacting factors shape soil properties, organic matter, and the development of soil horizons.
and soil development
, also called , occurs as rock and sediment are weathered and altered by water, air, and living organisms. The five interacting soil-forming factors are , climate, organisms, , and time. Together, they influence mineral content, organic matter, soil structure, and the development of layers called .
breaks down or changes rock and minerals at or near Earth’s surface. It occurs in three forms:
breaks rock into smaller pieces without changing its mineral composition. Water freezing in cracks and repeated heating and cooling are examples.
changes minerals through reactions with water, oxygen, or acids. It can dissolve minerals or form new ones, such as clay minerals.
results from the activity of organisms. Roots can widen cracks, while microbes and lichens can release compounds that alter minerals.
As soil develops, processes add, transform, move, or remove material. Dead leaves add organic matter, decomposition transforms it, water may carry dissolved substances or fine particles downward, and erosion may remove soil from the surface. These processes contribute to the formation of soil .
and climate
is the mineral or organic material from which soil develops. It may consist of weathered bedrock, river-deposited sediment, windblown material, or other deposits. Its mineral composition and particle sizes influence the developing soil’s texture, drainage, and available nutrients. A young soil often retains many properties of its .
Climate affects both the rate and type of soil development. Temperature and precipitation influence and biological activity: warm, moist conditions generally promote them, while cold or dry conditions often slow them. Water can dissolve and carry substances through soil by . Climate also influences vegetation, which affects the organic material entering the soil.
Organisms and organic activity
Plants, animals, fungi, bacteria, and other soil organisms shape soil through their effects on organic matter, structure, and nutrient cycling. Plants contribute leaves, roots, and other residues. Decomposers break down this material, releasing nutrients and forming soil organic matter.
Roots open pathways and help bind soil particles. Earthworms and burrowing animals mix soil and create pores. Together, these activities affect soil structure and nutrient cycling.
and soil movement
—the shape and position of the land—affects water movement, exposure to sunlight, and the movement of soil material. Steep slopes commonly lose soil through runoff and erosion, so soil may remain relatively thin. Water and sediment can collect in lower, flatter areas, where soils may become deeper or receive deposited material. Slope direction can also influence warmth and moisture.
Time and changing soil
Soil properties develop as soil-forming processes operate over time. Where the surface remains stable, , organic activity, and the movement of materials may gradually make more distinct.
Time alone does not determine soil development. Erosion, deposition, climate shifts, or disturbance can alter or interrupt the process. Older soil is not necessarily more fertile or better suited to a particular use.
How the factors interact
The five factors interact rather than acting independently. The same can develop into different soils under different climates or vegetation. On a steep slope, runoff may remove material faster than can develop; nearby, a flatter site may retain water and sediment.
Soil forms as changes and organisms add, decompose, and mix organic matter. Climate influences the rates of these processes, while affects water and material movement. Time allows soil characteristics and to develop, but erosion can remove material and slow or disrupt that development.