Land use & soil
"Dirt cheap" is exactly wrong. Soil is a thin, living, slow-made skin — centimetres that take centuries — and almost all our food grows in it. This powerbook follows three ways human land use destroys it faster than it can rebuild: salt rising to the surface, topsoil washing away, and metals poisoning the ground — and what it takes to heal each.
The interactive book above is the lesson. What follows is a plain recap you can revise from, plus the sources and how this maps to the syllabus.
Salinity: clearing and irrigation
The salt is usually already stored deep; land use mobilises it. Land clearing removes deep-rooted plants, so less water is used, the water table rises, and it carries stored salt up — dryland salinity. Irrigation raises the table too, and its dissolved salt is left behind as water evaporates, building up in the root zone.
Erosion and its prevention
Erosion strips fertile topsoil by wind and water; it accelerates on bare, cleared, over-grazed or ploughed ground. Prevention keeps the ground covered and slows the flow: cover crops, stubble and mulch, contour ploughing, terracing on steep land, and windbreaks.
Contamination and rehabilitation
Heavy metals (lead, cadmium, mercury, arsenic) from mining, industry, old paint/petrol and sludge are elements — they do not break down, are taken up by plants, and bioaccumulate up the food chain. Rehabilitation answers the cause: replant to lower a saline water table, restore cover to halt erosion, and remove, cap or treat contaminated soil — all slow, so prevention wins.
For HSC students
This powerbook covers the Salinity and Erosion thread of Module 4 (Human Impacts), framed by the inquiry question how does human use of land affect soil? Working through it, you should be able to:
- explain the causes of salinisation, including land clearing and irrigation;
- describe how salinity-affected areas are rehabilitated (a basis for a case study);
- account for soil erosion and evaluate prevention methods (a basis for the practical investigation);
- investigate sources and effects of soil contamination, including heavy metals.
The next chapter looks at introduced species and their effects on Australian ecosystems. Explanations here are original and are a study aid, not a copy of the syllabus.
Sources
- Australian and state agriculture/environment departments — dryland and irrigation salinity, causes and rehabilitation.
- CSIRO and Landcare resources — soil erosion processes and prevention, and land rehabilitation.
- Environmental-protection authority guidance — soil contamination, heavy metals and their effects.
- NSW NESA Earth and Environmental Science Stage 6 Syllabus (2017) — used only to scope the Module 4 content; explanations above are original.
Soil is the cheapest thing we own and one of the hardest to replace. Salt it, strip it or poison it in a season, and the land takes centuries to forgive us.