Environment within protected structures

Question 1

Describe environmental differences between protected environment and outdoors: temperature

Answer 1

• Temperature inside generally higher than outside. outside temperature caries according to the seasons.
• Temperature has an effect on rate of photosynthesis
• Easy to control in a protected structure
• Fluctuations in temperature are common in protected structures
• Reduce temperature through ventilation, shading, damping down.
  
  • Shading methods: shading material applied to cladding, shade paints for structure (outside), thermal screens for inside structure.
  • Max temp for tomatoes 32C, chrysanthemums is 30C
• Increase temperature with heating systems
  
  • min. temperature for tender plants may be up to 10C

Question 2

Describe environmental differences between protected environment and outdoors: humidity

Answer 2

• Relative humidity is measure of level of moisture in the atmosphere
  
  • RH = actual humidity of air as a proportion of potential humidity of the air at a given temperature.
• Humidity is linked to temperature - warm air can hold more water than cold air - RH falls as temperature rises
• Most plants have preferred RH 40-75%
  
  • above 75% increased risk of fungal disease e.g. botrytis. Plants will lose less water through transpiration when the RH is high and therefore will not take up water and nutrients which will affect plant growth. Excess humidity can lead to plant oedema.
  • below 60% plants lose more moisture via transpiration, leaf scorch, plant wilting.
• Ventilation reduces humidity levels, as does raising temperature in a protected structures
• Damping down and/or reducing air flow increases RH
• Relative humidity is higher with less fluctuation in a protected environment as plants transpire and water evaporates from the ground and paths around the plants.
  
  • Lower relative humidity outside due to wind/rainfall/air temperature

Question 3

Describe environmental differences between protected environment and outdoors: light

Answer 3

• Light is essential for photosynthesis
• Natural light levels in protected structures are generally lower than outdoors
  
  • Cladding and structural components(e.g. shadows) reduce light levels
  • Light transmission is affected by the shape of the structure
  • Site factors and orientation affect light levels
• Light increases temperature so if temperature is excessive shading may be used which reduces amount light reaching plant
• Supplementary lighting: additional artificial lighting used, if insufficient light, in conjunction with natural lighting to
  increase the photosynthesis rate and achieve optimum growth e.g. to extend day length.
  
  • The light source must be efficient e.g. low sodium vapour lights.
• Insufficient light causes poor spindly growth, more prone to pests and diseases.

Question 4

Describe environmental differences between protected environment and outdoors: concentration of atmospheric gases

Answer 4

• Photosynthesis requires carbon dioxide
  
  • Carbon dioxide is taken in by plants during the day for photosynthesis and is given out during the night in respiration, therefore, CO2 levels are much higher at night in a sealed greenhouse.
  • If CO2 levels not sufficient then plant growth will be affected - it is a limiting factor
  • Commercial growers often add supplementary CO2 to increase crop yield. e.g. using CO2 burners
  • CO2 levels inside structure lower than ambient levels (outside)
• Oxygen essential for plant to photosynthesis, enabling growth. Maintain levels of oxygen so plant can respire and give off oxygen.
• Open vents to allow exchange of gases
• Improve horizontal air flow to distribute available CO2 evenly throughout the crop e.g. with forced draught or fan ventilation systems.

Question 5

Describe environmental differences between protected environment and outdoors: air movement

Answer 5

• Air movement controlled by ventilation, convection currents take place as environment warms up.
• Ventilation is key in a protected structure
• Lack of ventilation can lead to build up of P&Ds
• Forced draught or fan ventilation systems improve natural air movement.
• Wind will increase the rate of transpiration (evaporation rate increases). No wind in a protected structure; transpiration rate is reduced.

Question 6

Describe environmental differences between protected environment and outdoors: irrigation

Answer 6

• Most protective structures prevent rainfall reaching plant
  
  • All watering must be controlled e.g. by automatic irrigation (commercial) or hand watering / capillary tray systems (home gardener)
• Fluctuations in temperature require equivalent watering regimes
• Cloches will need to be moved for watering

Question 7

Summary of environmental differences between outdoors and protected environment

Answer 7

• Temperature: ambient temperature, cannot be regulated outdoors / heating can give winter front protection, shading is needed in summer
• Humidity: lower than inside, depends on weather conditions / can be adjusted by ventilation to increase air movement or damping down
• Light: levels depend on daylight / can be controlled by shading or providing supplementary or replacement lighting to adjust day length and quantity of light
• CO2: ambient levels, cannot be changed / levels may be supplemented to improve rates of photosynthesis (enrichment)
• Air movement: depends on weather / can control humidity levels and minimise disease, ventilation by natural air movement, forced draught or fan
• Irrigation: may irrigate on large scale / irrigation and be controlled e.g. overhead irrigation or sub-irrigation for containers and border soil.

Question 8

Benefits and limitations for protected structures for growing tomato (Lycopersicon esculentum)

Answer 8

Benefits:

• Growing environment is controlled and improved therefore higher yields
• Improved crop quality due to controlled environment
• Extends growing season - longer season of fruiting and ripening, and plants mature more quickly under protection
• Greater range of cultivars can be grown.
• Environmental conditions outdoors, such as wind, does not damage plant; less physical damage ensures optimum growing conditions = higher yield
• Protection for some P&D, for example Blight
• Can use biological controls more easily

Limitations:

• Temperature extremes; excessive heat stunts growth or leads to wilting. Heat may build up if not adequately ventilated or floor damped down
• Have to provide ALL irrigation
• Less natural pollination hence the need for bees to be introduced to the crop or agitation techniques on specific crops.
• Costs are higher in production than an outdoor crop, especially out of season e.g. heating costs, costs of protected structure
• Pests and Diseases specific to glasshouse e.g. whitefly or red spider mite.
  
  • Pests can reproduce more quickly due to environmental conditions.
  • Diseases can establish more quickly due to higher temperatures.

Question 9

Describe the effect of different environmental factors on plant growth in a protected environment (and their control)

Answer 9

• Low air temperature: plant growth slows down, resulting in stunted growth, poor fruit set, and cell damage (heat during winter months, bubblewrap greenhouse). Extreme low temp can cause frost damage.
• High air temperature: plant growth reduced, wilting (increase ventilation and damping down to lower temperature)
• Good air movement: sturdier growth, less disease problems. Excessive air movement can damage plants. Low levels of air movement reduce transpiration and therefore rate at which plant takes up water a nutrients and level of humidity around plant.
• High RH: higher chance of fungal disease problems within crop, reduced water and nutrient uptake by plant (increase ventilation to lower RH, or increase temperature. Use low level irrigation)
• Low RH: Excessive water loss/increases rate plant dries out, plant susceptible to red spider mite (damp down environment, reduce ventilation / air flow, misting / overhead irrigation)
• Low natural light: cause spindly/weak etiolated growth due to reduced photosynthesis, reduced flowering, plants more susceptible to P&D (provide supplementary lighting, improve light entry into structure)
• High natural light: compact healthy growth with short internodes, good bud initiation and flower development (if too bright can cause leaf scorch so shade if needed)
• Low CO2: reduced rate of photosynthesis, so reduced growth, poor yield and weak plants
• Good CO2: increased rate of photosynthesis, higher yields
• Erratic irrigation: splitting or damaged fruit, leaf scorch, root loss (regular watering schedule)
• Overwatering: root rot and oedema symptoms (use moisture meter, check with finger for dryness)

Question 10

Effect of environmental factors on named plants in a protected environment

Answer 10

• Effect if insufficient light on tomatoes: etiolated growth, which is weak and spindly. Poor fruit set. Susceptibility to pest and disease, poor fruit ripening.
• Effect of erratic/irregular irrigation on tomatoes:
  
  • Under-watered - causes wilting, resulting in loss of growth and cell damage.
  • Over-watered - roots rot, reduces water and nutrient plant uptake.
  • Erratic watering - Blossom end rot disease, fruit splits, root damage and leaf
    scorch.
  • • Also see table on pg 10 of notes

Question 11

Describe the suitability of a greenhouse for production of main season tomato crop

Answer 11

• Green house is tall structure which is able to accommodate a tomato crop
• It is economic to heat a greenhouse and will allow a tomato crop to be grown economically
• A greenhouse has ventilation to enable control of temperature and relative humidity
• Has excellent light transmissions to maximise quality and yield of crop.

Question 12

Named disorders that can damage a tomato crop

Answer 12

• Blossom end rot:
  
  • Caused by calcium deficiency.
  • Young leaves become chlorotic and fruit may start to go brown and rot.
  • Controlled by ensuring plants not fed excessive levels of potassium and watered regularly to prevent drought stress.
  • Ground limestone or calcium hydroxide can be added.
• Fruit splitting:
  
  • Usually occurs when rapid growth is induced following over watering after allowing plants to dry out.
  • Can be controlled by ensuring growing media is water retentive and by careful and regular watering.