3.2 Protected Environments

Question 1

Importance if ventilation

Answer 1

Very high temperatures can scorch tender plants.
Glasshouses need at least one ventilator.
Ventilators should represent one sixth of floor area.
Temperature should be kept below 27oC

Question 2

Chimney effect with top and side vents open.

Answer 2

Air in glasshouse is generally warmer than the outside.
When top vents are opened the warm air rises and escapes.
Cooler air is pulled in from the side vents.
Circulation air pattern (chimney effect) is established.

Question 3

Irrigation

Answer 3

Optimum supplies of water are needed.
Soil structure is important to ensure that soil holding capacity is managed at optimum level.
Soil should have good physical structure and organic matter levels.

Irrigation is important to ensure that optimal levels of water are given to crops.
Irrigation should satisfy moisture sensitive stages eg flowering/fruiting.

Question 4

Carbon dioxide - in a protected environment.

Answer 4

In a sealed environment, without ventilation, the amount of available co 2 will deplete.

Co 2 is necessary for plant growth.

In commercial greenhouse the CO2 level aimed for is 1000ppm.
Special CO2 burners are used or waste heat and CO2 can be used.

Question 5

Damping down.

Answer 5

Reduces high summer temperatures.
Areas of greenhouse are syringed with water.
Water evaporates> temperature is reduced.
Can be done manually, with hose or automatically with mist nozzles.
Walk ways, paths, under benches and empty benches can be sprayed.
Foliage can be sprayed but care should be taken to avoid disease.

Question 6

Shading

Answer 6

Examples of shading - liquid shading compound, shade cloth.
Applied to the outside of glasshouse structure.
Reduces heat, especially in summer, by decreasing amount of solar energy entering through the glazing.
Light intensity is reduced.
Cam be automated, depending on amount of sun.

Question 7

Forced air ventilation in large greenhouse.

Answer 7

Forced air ventilation increases efficiency of excess heat removal from glasshouse.
Mechanical fans (exhaust fans) create negative pressure within the structure.
Cooler air from outside rushes in to fill the void, through side vents.

Question 8

Controlled atmosphere storage.

Answer 8

Storage technique where interior concentration levels of oxygen, carbon dioxide and nitrogen as well as temperature and humidity levels are monitored and controlled to preset levels to suit the storage needs of a particular crop.