Preventing environmental degradation is far more cost-effective than rehabilitating degraded land. However, where degradation has already occurred, rehabilitation techniques can restore land to productive and ecological function. This knowledge area requires students to understand techniques for preventing and rehabilitating degradation across land, soil, water and air.
KEY TAKEAWAY: Prevention focuses on maintaining soil cover, health and hydrology before degradation occurs. Rehabilitation restores function to already-degraded land. Both are necessary for sustainable agriculture and horticulture.
For water erosion:
- Contour farming: Cultivating along the contour (lines of equal elevation) rather than up-and-down slope; reduces runoff velocity and keeps water on the paddock
- Contour banks (earthen banks): Physical structures that intercept and redirect surface runoff, preventing rill and gully formation
- Cover crops and ground cover maintenance: Vegetative cover absorbs raindrop impact energy, reducing splash erosion; aim for >70% ground cover at all times
- Waterway revegetation and grassed waterways: Vegetated channels slow runoff and filter sediment before it reaches streams
For wind erosion:
- Windbreaks / shelterbelts: Rows of trees and shrubs perpendicular to prevailing winds; reduce wind speed and protect bare soil
- Minimum tillage / no-till practices: Maintain stubble and residues on the surface; reduces the exposure of bare, loose soil to wind
- Stubble retention: Retaining crop residues after harvest provides temporary ground cover
EXAM TIP: A key VCAA distinction is between erosion prevention (stopping soil loss before it happens) and erosion control (managing erosion once it has begun). Make sure your responses address both where relevant.
| Degradation | Rehabilitation Technique | Mechanism |
|---|---|---|
| Erosion (gullies) | Gully reclamation (rock chutes, silt fences, revegetation) | Stabilise the gully head, slow water flow, allow vegetation establishment |
| Salinity | Salt-tolerant plant establishment; drainage installation; revegetation of recharge zones | Reduce water input to groundwater; manage salt expression at surface |
| Compaction | Deep ripping / subsoil tillage; biological amelioration via deep-rooted plants | Mechanically break up compacted layers; improve infiltration |
| Soil acidity | Agricultural lime (CaCO₃): applied at rates of 1–5 t/ha based on soil test; neutralises acidity and raises pH | CaCO₃ + H⁺ → Ca²⁺ + H₂O + CO₂ |
| Nutrient depletion | Targeted fertiliser application; organic amendments (compost, manure) | Replace removed nutrients; restore organic matter |
COMMON MISTAKE: Students often state that lime adds nutrients to the soil. Lime’s primary role is to neutralise acidity (raise pH) and reduce aluminium toxicity — it is not a nutrient fertiliser. Calcium is a secondary benefit.
While soils and water are the primary focus in AHS, air quality in agricultural contexts includes:
Revegetation with appropriate native species addresses multiple degradation types simultaneously:
STUDY HINT: In exam questions, link the rehabilitation technique to the specific degradation mechanism it addresses. A complete answer explains why the technique works, not just what it is.
VCAA FOCUS: Rehabilitation questions often require you to evaluate techniques. Consider: How effective is it? How long does it take? What are the costs? Are there any negative side effects? For example, deep ripping addresses compaction but must be followed by strategies to prevent re-compaction, or the benefit is temporary.
APPLICATION: A mixed cropping property in the Mallee showing signs of wind erosion (loss of fine topsoil, drift around fence lines) should implement: (1) immediate stubble retention to provide surface cover; (2) establishment of a shelterbelt on the prevailing wind side of the most exposed paddocks; (3) transition to minimum-tillage or no-till practices; and (4) soil testing to assess any associated nutrient losses requiring fertiliser response.
