Soils form at the interface between land, the hydrosphere and the atmosphere. Their formation and placement are the result of complex interactions between differential weathering of primary minerals in rocks, formation of secondary clay minerals, sculpting of landforms, transport and movement of weathered material downhill, accumulation of colluvium and alluvium downslope, leaching and soil horizon formation, and, finally, stabilisation by vegetation.
Our soils, landforms and vegetation have co-evolved over millions of years; their health and condition are inextricably linked. Soil type, depth and condition have an influence on the growth and condition of all types of vegetation. At the same time, changes to vegetation caused by fire, clearing, grazing and harvesting affect the condition of our soils.
If well managed and maintained, the soil system performs many functions or ‘ecosystem services’. It:
- stores and filters water
- stores and cycles nutrients
- stores and filters waste products
- stores carbon (it is the largest reservoir of terrestrial carbon)
- hosts plant, animal and microbial biodiversity
- supports agriculture
- provides raw materials (e.g. clay, sand, gravel)
- stores our palaeontological, archaeological and cultural heritage.
However, when not managed properly, soil can decrease these ecosystem services and affect other ecosystem services; for example, clean air can be affected by dust storms, and sediment in water can change river flow patterns, and reduce habitat quality in riparian and coastal marine ecosystems.
Soil is essentially a nonrenewable resource, because it forms and regenerates slowly, over thousands of years, but can degrade rapidly. Some types of degradation, such as nutrient depletion, can be corrected by fertilisation, but this correction may be costly and have negative offsite impacts. Other forms of degradation, such as soil erosion and salinity, are more difficult to remedy. Prevention is the key to avoiding land degradation. However, natural soil constraints on agriculture and the interaction with climate have made it difficult to develop sustainable systems of land use.
Soil is effectively privately managed across much of Australia. However, the impact of healthy, functioning soils on the environment as a whole—such as improving water quality, protecting biodiversity and mitigating excess greenhouse gases—means that soil is also a large public good.