GCSE Agriculture and Land Use CCEA

Soil Formation and Types

Soil Formation

• Soil formation, or pedogenesis, is a process that involves the weathering of rocks and the decomposition of organic matter.
• The parent material (the weathered rock or sediment that is the basis of the soil) significantly affects the properties of the resulting soil.
• Weathering could be physical (mechanical), involving physical breakdown of rocks into smaller particles, or chemical, involving the alteration of the rock's chemical composition.
• Biological activity, such as the action of bacteria, fungi, worms, insects, and plant roots, aids in the decomposition of organic matter, and alongside weathering, it plays a key role in soil formation.
• Time is also a considerable factor in soil formation. It can take hundreds to thousands of years for a fully matured, rich and fertile soil to form.

Types of Soil

• There are generally three types of soil which are based on the size of the particles that make up the soil. These include sand, silt, and clay.
• Sandy soil has large, coarse particles. It has lots of air gaps, making it free-draining, which means water can easily pass through it. It warms up quickly in spring.
• Silty soil has medium-sized particles. It has a silky texture and retains water well. It's fertile and helps plants retain nutrients.
• Clay soil has the smallest particles. It feels sticky in your hands. It gets compacted easily and does not drain well, leading to water logging. However, it is nutrient-rich and good for growing plants.
• Most soils are not just sand, silt, or clay, but a combination known as loam. Loam soil is considered ideal for gardening and agricultural uses because it retains nutrients and water, while still allowing for water drainage.
• Soils can also be classified according to their pH, or acidity level: acid soils (pH below 6), neutral soils (pH around 7) and alkaline soils (pH above 7). The soil's pH can affect the availability of nutrients for plant growth.