2 - Control of Protective Environments

Question 1

Name and describe five environmental factors important in the care of plants growing in a protected environment.

Answer 1

Temperature: Reduced air or soil temperature will reduce the rate of photosynthesis, reduce the growth rate, and the rate of respiration in the plant

Relative humidity: A low level of humidity will cause an increase in transpiration, leaf scorch and permanent or temporary wilting of the plant

Natural light: A lack of natural light will cause we, spindly growth, softer growth, and make plants more prone to attack by pests and diseases

Water availability: A lack of water will cause permanent or temporary wilting, affect the plant’s ability to uptake nutrients and to carry out photosynthesis

Availability of carbon dioxide and oxygen: a lack of carbon dioxide or oxygen will affect the growth rate of the plant and the level of yield of any crops.

Question 2

Describe how a grower can maximise natural light transmission in a protected structure by:

• Site selection
• Selection of protected structure
• Growing within the structure.

Answer 2

Site selection: Choose a site not shaded by trees, hedges, buildings. Choose and orient along east-west axis to maximise natural light.

Selection of protected structure: Select a structure with a curvilinear or mansard construction with high eaves to maximise light transmission. Use strong construction materials (e.g. steel) which also don’t block too much light. Clad in horticultural glass to maximise light transmission.

Growing within the structure: Use staged benches to enable several tiers of plants and avoid shading some plants. Use a reflective material to bounce light back onto the plants. Train and support plants.

Question 3

Describe one effect of irregular watering on a named crop.

Answer 3

Erratic watering can cause blossom end rot in tomatoes and cause fruit to split.

If the roots go from drought conditions to saturated, the roots will be damaged and leaves may scorch.

Question 4

Describe two methods of changing the relative humidity in a protected environment?

Answer 4

Damping Down: Spraying water on concrete paths, benches and sometimes the plants to encourage surface evaporation. Damping down in dry, hot conditions will also reduce air temperature by leading to an increase in the rate of evaporation. Raising humidity can discourage some pests.

Forced Ventilation: Using extractor fans to draw air across the glasshouse. Enables positive air movement across the crop, which ensures efficient gaseous exchange. Lowers relative humidity resulting in fewer fungal diseases.

Question 5

Describe two specific irrigation systems used in protective environments.

Answer 5

Drip: Water is delivered to the base of the plant by drips from a pipe. Water passes through a series of pipes which get smaller as they get nearer the plant. Can be operated on a timer.

Capillary: A system of irrigation that relies on water moving up by capillary action from a wet or flooded bench, which may have capillary matting or sand at its base. The plant determines how much water it requires and takes it up by capillary action. The bench is either always wet or periodically flooded.

Question 6

Describe two effects on plant growth for each environmental factor:

• Good air movement
• High natural light
• High relative humidity
• Erratic irrigation
• Carbon dioxide concentration.

Answer 6

Good air movement:

• Sturdier growth
• Less prevalence of disease

High natural light:

• Compact healthy growth with short internodes
• Good bud initiation and flower development

High relative humidity:

• Higher incidence of disease
• Less water loss, reduced irrigation required

Erratic irrigation:

• Possible splitting or damage to fruit production
• Possible leaf damage caused by leaf scorch or root loss

Carbon dioxide concentration:

• If concentration of CO2 is good, rate of photosynthesis will increase
• Higher level of crop productivity.