4.1.4 Types of Environmental Degradation

In Australia, the following types of soil and water degradation are the most significant threats to food and fibre production.

Erosion

Erosion is the removal of topsoil by wind or water. Topsoil contains the majority of the soil's nutrients and organic matter.

• Cause: Clearing vegetation or overgrazing, which leaves the soil bare and exposed.

• Impact: Loss of fertility and the silting up of local waterways, which can kill aquatic life.

Salinity

Salinity occurs when salt concentrations in the soil or water reach levels that are toxic to plants.

• Cause: Dryland salinity often happens when deep-rooted native trees are replaced with shallow-rooted crops. This allows the water table to rise, bringing underground salts to the surface. (Note that 'dryland' refers to land that is not watered by anything other than natural rainfall - not irrigated.)

• Impact: Most crops and pastures die, leaving the ground bare and prone to further erosion.

3. Waterlogging

Waterlogging happens when the soil pores are completely filled with water, leaving no room for oxygen.

• Cause: Poor drainage, heavy clay soils, or excessive irrigation.

• Impact: Plant roots suffocate without oxygen, leading to root rot and total crop failure.

4. Compaction

Compaction occurs when the air spaces between soil particles are squeezed out.

• Cause: The use of heavy machinery on wet soil or high stocking rates of heavy-hooved animals like cattle.

• Impact: Roots cannot penetrate the hard soil, and water cannot soak in, leading to increased runoff and poor plant growth.

5. Soil Acidity

Soil acidity refers to a decrease in the soil pH (becoming more acidic).

• Cause: Long-term use of nitrogen-based fertilisers and the removal of alkaline plant material during harvest.

• Impact: Essential nutrients become locked in the soil and are unavailable to plants, while toxic elements like aluminium become more soluble and can poison roots.

6. Soil Nutrient Depletion

This is the gradual loss of essential nutrients like nitrogen, phosphorus, and potassium.

• Cause: Harvesting crops or moving livestock off-farm without replacing the nutrients they took from the soil.

• Impact: Steadily declining yields and poor quality food and fibre products.

PRACTICE

Create a document and make a table. Find photos and written examples of each type of soil degradation, then add columns for causes, signs and amelioration techniques.

Exam-Style Questions  Use the marking scheme to evaluate your work 

Question 1 (2 Marks)

Describe the relationship between clearing native vegetation and the development of dryland salinity.

Question 2 (4 Marks)

A vegetable grower in Gippsland has found their soil pH has dropped from 6.5 to 5.2 over the last decade. Analyse the impact this will have on plant nutrient uptake and identify one management strategy to reverse this degradation.