The Earth Contents

5. Soils

The characteristics of different soils depend on the complex physical and chemical processes occurring in them

Individual soil particles group together into what are called aggregates, which are central to the formation of soil structure. Soil structure is important as a factor in determining the water-holding capacity of the soil and the speed at which water soaks into and through the soil. This is in turn a vital factor in determining the soil's capacity to support plant growth. Soils made up of extremely small particles (0.1-10µm) called colloids, and their properties are related to the fact that these small particles have an extremely large surface area-to-volume ratio. In a soil, the clay particles fall into this size range. They are dispersed in water, and because of the electrical charges on the particles they repel each other and remain in suspension. The amount of colloids present in a soil influences the water holding capacity, as water is retained in small and medium-sized pores. Water is also adsorbed on to clay minerals and organic matter as a film round the particles.

The characteristics of different soils depend on the complex physical and chemical processes occuring in them

Why is soil structure important for plant growth?