Environmental control and modification refers to deliberate changes made by producers to the physical growing environment to improve conditions for plant and animal production, reduce risks from adverse weather, pests or soil conditions, and increase efficiency. These modifications operate across three domains: microclimate, soil or growing media, and topography.
KEY TAKEAWAY: Modifying the growing environment allows producers to extend seasons, improve yields, reduce input losses and manage risk — but each technique must be evaluated for its energy use, cost, and environmental impact.
A microclimate is the climatic conditions in a small, localised area — different from the general regional climate. Producers modify microclimates to protect plants and animals from extremes of temperature, wind and frost, and to extend the growing season.
Rationale: Wind increases evapotranspiration, lowers temperatures, causes physical damage (fruit bruising, stem breakage), dries soils and increases wind erosion.
Implementation: Rows of trees and/or shrubs perpendicular to prevailing winds. A windbreak 10 m tall provides effective protection for 100–150 m on the leeward side.
Co-benefits: Habitat for wildlife and beneficial insects, carbon sequestration.
Considerations: Windbreaks compete with adjacent crops for water, nutrients and light near the tree row.
Rationale: Creates a controlled microclimate, decoupled from external conditions. Allows year-round production, elimination of rainfall-driven disease pressure, and precise control over temperature, humidity and CO₂.
| Structure | Features | Best Use |
|---|---|---|
| Glass greenhouse | High light transmission, durable, good thermal properties | High-value crops (tomatoes, cucumbers, flowers) |
| Plastic polytunnel | Low capital cost, flexible, seasonal extension | Strawberries, soft fruit, cut flowers |
| Shade cloth structures | Reduces solar radiation and temperature | Leafy vegetables in summer, orchid/fern growing |
| Insect-exclusion netting | Prevents insect pest entry; allows airflow | Premium stone fruit, integrated pest management |
EXAM TIP: When discussing protected cropping, evaluate sustainability carefully. Energy for heating/cooling has a carbon footprint, but protected cropping can also reduce water use, eliminate fungicide use and produce higher yields per unit area — these trade-offs must be acknowledged.
pH adjustment:
- Lime (CaCO₃): Applied to raise soil pH; neutralises acidity; typical rate 1–5 t/ha based on soil test
- Sulfur or iron sulfate: Applied to lower soil pH for acid-loving crops (blueberries, azaleas)
- Dolomite: Lime source also containing magnesium
Nutrient management:
- Fertilisers (inorganic or organic): Supply deficient nutrients; rates determined by soil testing and nutrient budgeting
- Compost and manures: Improve organic matter content, biological activity and soil structure
- Green manures: Cover crops incorporated into soil; add organic matter and fix atmospheric nitrogen (if legumes)
Soil structure improvement:
- Gypsum (CaSO₄·2H₂O): Flocculates dispersed clay soils (particularly sodic soils); improves structure and water infiltration without significantly altering pH
- Deep ripping: Mechanically breaks up compact subsoil layers; allows root penetration to deeper moisture and nutrient reserves
In protected cropping and nursery production, growing media replace or supplement soil. Common components include:
| Component | Function |
|---|---|
| Peat moss or coir | Water retention, light weight, organic matter |
| Perlite or vermiculite | Drainage, aeration, structural support |
| Pine bark | Drainage, physical stability |
| Slow-release fertiliser | Nutrient supply over extended period |
Hydroponics: Plants grown in nutrient solution without solid growing media; maximum water and nutrient use efficiency; requires precise management of pH and EC of nutrient solution.
COMMON MISTAKE: Students sometimes describe all growing media as ‘soil substitutes’ without recognising the fundamental difference: soil supports self-regulating nutrient cycles; growing media are inert substrates requiring complete external nutrient provision.
Topographic modification involves reshaping the land to improve drainage, water distribution and slope stability.
On steep slopes, terracing converts sloping land into a series of level steps:
- Bench terraces: Flat benches with retaining walls; high capital cost but allows cultivation on steep terrain
- Broad-based terraces: Gently sloped surfaces that allow machine cultivation
Rationale: Reduces slope length, decreases runoff velocity, promotes infiltration and prevents gully formation.
STUDY HINT: Topographic modification is often capital-intensive. Always consider the cost-benefit ratio — laser levelling of irrigated country is economically justified by water savings; terracing steep horticultural land may only be justified for very high-value crops.
VCAA FOCUS: VCAA may ask students to justify (give reasons for) a particular modification technique in a given scenario. Always link the technique to a specific problem it solves and a sustainability benefit it provides.
APPLICATION: A stone fruit orchard on a gently undulating site with a history of waterlogging in winter could benefit from: (1) subsurface mole drainage to remove excess water; (2) raised beds or mounded planting rows to keep root zone above seasonal water table; (3) frost fans on the valley floor to protect blossoms; and (4) windbreaks on the exposed western boundary to reduce wind damage and desiccation.
