Lecture 3

Particle size and Soil texturalclasses• Soil texture is considered a basic property of the soil because thetextural class of a particular soil generally remains unchanged overtime equivalent to the human lifespan. This is one reason soildescriptions used in soil surveys record the soil textural class ofeach horizon. However, disturbance of an area, such as water orwind erosion, could alter the textural class of the soil surface boththe soil being eroded and the soil where the erosional depositionoccurs. Over long time periods (geologic time), weathering andtranslocation of soil materials can change soil texture.• Aggregates and Soil StructureSoil particles that are held together by chemical and physical forcesform stable aggregates. Natural aggregates are called peds.Collectively, the type of soil aggregates or peds defines soilstructure. Soil structure (Figure 3.2) influences the amount of waterthat enters a soil (infiltration) and gas diffusion at the soil surface.