4.1.9 Environmental control and modification

Key Knowledge: techniques and rationale for environmental control and modification in agriculture and/or horticulture: modification of microclimate; soil or growing media; topography 

Techniques for Modification:

• Greenhouses and Poly-Tunnels: These structures trap solar radiation (the greenhouse effect) to raise temperatures during winter. Automated systems modify the environment further using; shade cloths to lower UV stress, misting fans to increase humidity, and automated vents to manage carbon dioxide (CO2) levels.

• Frost Fans and Overhead Misters: On freezing spring nights, large automated fans pull down warmer air from an atmospheric inversion layer to keep orchard temperatures above 0°C. Alternatively, overhead misters apply a fine spray of water. Counterintuitively, as the water freezes on the plant, it forms a protective layer, insulating the delicate blossoms from frost damage.

• Windbreaks and Shelterbelts: Planting rows of trees at right angles to the prevailing winds, slows down wind speed across paddocks. This reduces damage to crops, minimises topsoil erosion, and lowers the evaporation rate of soil moisture.

Modification of the Soil or Growing Media

If the native soil has physical or chemical limitations that restrict plant growth, producers will alter its structure or bypass it entirely.

• Hydroponics and Substrates: Horticulturalists often remove soil from the equation entirely, growing plants in inert media like rockwool, coco peat, or perlite. This allows for total control over root nutrition, as water containing precise mixes of dissolved fertilisers is pumped directly to the plants.

• Soil Amendment (Adding Gypsum, Lime, and Organic Matter): On broadacre farms, heavy clay soils can be modified by adding gypsum (calcium sulfate), which binds fine clay particles into larger clumps, improving drainage and root penetration. Lime is added to raise pH, while compost adds organic carbon to boost water-holding capacity.

• Plastic and Organic Mulches: Laying plastic sheeting or organic straw over soil rows suppresses weeds, keeps soil temperatures warmer in spring, and acts as a physical barrier to stop soil moisture from evaporating.

Modification of Topography

Topography refers to the shape, slope, and features of the land surface. Modifying topography is a long-term engineering investment designed to manage how water moves across the property.

• Laser-Guided Land Levelling: Using laser-directed earthmovers to flatten paddocks to a precise, gentle slope. This is commonly used in flood-irrigated industries like rice or cotton production to ensure water flows evenly across the entire field without pooling in low spots or leaving high spots dry.

• Raised Beds and Furrows: In areas prone to heavy winter rains, soil is shaped into elevated rows (raised beds) separated by low channels (furrows). Plant roots sit safely in the aerated soil of the bed, while excess water drains into the furrows, preventing waterlogging.

• Terracing: On steep hillsides, cutting flat steps into the slope transforms a vulnerable incline into a series of manageable, flat shelves. This drastically slows down water runoff, stopping gravity from causing severe water erosion and landslides.

PRACTICE  Use the marking scheme to evaluate your work

Exam-Style Questions

Question 1 (2 Marks)

Explain the biological rationale for utilising automated frost fans in a commercial vineyard such as Curly Flat, during early spring.

Question 2 (4 Marks)

A vegetable grower chooses to farm on a sloping hillside. Analyse the environmental risks of leaving the topography unmodified, and propose one structural modification to manage water movement safely.

Exam Tip: Where's the Trade-off?

When evaluating environmental modification techniques in an exam, high marks are awarded to students who can discuss the trade-off between input costs and production predictability.

• The Rule: The more environmental control you want, the higher the financial capital required.

• The Comparison: A protective hail netting grid over an apple orchard provides reliable physical protection and stabilises yield (high predictability), but requires substantial upfront money. Broadacre cropping relies entirely on natural rainfall (low predictability) but operates with much lower structural setup costs per hectare.

SAC Tip: 

A major commercial rationale for microclimate modification is season extension—being the first to get a product to market when supply is low and prices are high.

If a SAC question asks for the economic rationale of using poly-tunnels or greenhouses, you can write a gread response following this commercial logic:

1. The Modification: Utilising poly-tunnels warms the air and soil profile in late winter.

2. The Biological Response: This triggers early root activity and bud-burst, bypassing natural winter dormancy.

3. The Economic Outcome: The producer harvests and sells their crop weeks before open-field competitors, capturing peak market prices when consumer demand is high but volume is low.