Soil is a living thing; a single teaspoon of soil contains billions of tiny organisms. Soil’s delicate and complex structure is formed over thousands of years. Healthy soil acts as a spongy reservoir for water and nutrients, and plays a vital role in the earth’s carbon and nitrogen cycles.
The typical undisturbed soil profile of the Cumberland Plain is derived from shale and, through tens of thousands of years, has weathered to form distinct layers. The top 40 cm of the profile (the A horizon) is relatively light in texture and is slightly acidic (pH 6), allowing good plant growth. It is home to worms and other creatures. Unfortunately, this part of the profile is often washed away or removed during excavation for new buildings.
The subsoil (the B horizon), which is orange in colour, is not very good for plant growth as it has a higher clay content and pH, holds water and does not supply good aeration for the roots. However, during dry times, this layer helps supply deep-rooted plants with vital moisture.