From R2114 Feb ’18
Q2 a) Name TWO environmental factors that a grower would need to control to maintain ideal growing conditions within a protected environment. [ 2 marks]
b) Describe ONE distinct effect on a growing crop for EACH of the factors named in a). [4 marks]
c) Describe how EACH of the factors named in a) can be controlled. [ 4 marks]
This question relates to the following parts of the syllabus:
2. Know the environment provided by a range of protected structures.
2.1 Describe the environmental differences between the protected environment and outdoors including temperature; humidity; light; concentration of atmospheric gases; air movement; and irrigation requirements.
To include: outdoor variability and seasonality, contrasted with indoors – control and supplementation.
Protected environment details: for air and soil temperature - the range of growing conditions from frost-free winter protection to the requirements for shade in summer; for relative humidity the importance of air movement, damping down; for light – supplementing and replacement lighting, day length and quantity of light; for concentration of atmospheric gases – possibility of carbon dioxide becoming a limiting factor for photosynthesis; carbon dioxide enrichment reasons and methods; air movement – ventilation by natural air movement, forced draught or fan ventilation; for humidity control
and to minimise disease transmission; irrigation requirements – methods of overhead watering and sub-irrigation for crops grown in containers and in the border soil.
2.2 State the benefits and limitations of using protected structures for growing plants, (for example tomato, Lycopersicon esculentum) compared with growing the same plants outdoors.
Examples to include: tomato (Lycopersicon esculentum, also called Solanum lycopersicum).
Benefits arising from the control and supplementation listed in 2.1; higher yields and quality; longer season of fruiting and ripening; can grow a greater range of cultivars.
Limitations – relative costs; effort required; different pest and disease problems indoors.
2.3 Describe the effect of the environmental factors listed in 2.1 on plants in a protected environment.
To include examples using named plants and horticultural situations.
4. Understand the control of the environment in protected structures.
4.1 Describe the factors that affect light levels in protected structures, including shape of structure; site factors; orientation; type and condition of cladding materials.
To include: shape of structure – Venlo, widespan, Mansard, curvilinear; Angle of incidence. aesthetics; site factors – exposed/sheltered, latitude; orientation – E-W, N-S; type (see 3.2) and condition of cladding materials – new, scratched, dirty, screened/painted with shading compound.
4.2 Describe how the temperature can be maintained in structures including heating by gas, oil or electricity; heat distribution using circulating water and air; cooling by forced or natural ventilation; evaporation; and shading.
To include information on methods of heating and cooling protected structures; relative costs compared to other heating systems; and practical considerations such as reliability/supply to site.
4.3 Describe methods of changing the relative humidity (RH) in a protected environment, including the effects of ‘damping down’, ventilation and temperature changes.
State what is meant by ‘damping down’. Describe patterns of ventilation in a structure which will help adjust relative humidity. The use of forced draught or fan ventilation and natural ventilation systems. Describe how changes in temperature affect relative humidity which in turn affect water and nutrient uptake.
4.4 Describe manual and automated methods of irrigation including the use of watering cans, hose pipes, capillary systems and ‘drip’ systems.
To include the benefits and limitations of different watering methods (for example the potential for disease from overhead watering of some crops). Containerised crops and crops grown in border soil.
To include the use of: shading, blinds and paints to avoid overheating in protected structures; supplementary lighting to extend the growing season; and, in outline only, use of artificial light/dark periods to prepare poinsettia crops.
4.6 Describe the importance of cultural and biological controls to limit the damage caused by plant pests and diseases.
State what is meant by cultural and biological controls; Describe the use of cultural controls to limit two pests or diseases. Give two examples of how biological controls are used for specific pests (Latin names for biological controls are not required: type of control - nematode, mite, wasp, ladybird – is sufficient with the correctly identified pest.) State the advantages that cultural and biological control have over chemical control methods.
As can be seen, this is a question which covers a large part of the syllabus. It can also be answered using several different factors. It is important to read through all parts of the question and think about the environmental factors you are going to name for part a) before answering. You need to be able to describe the effects for part b) and how to control them for part c), and there may be some factors that you find easier to use as answers than others.
For part a) the examiners’ comments suggest the following factors that could be named as including:
Air temperature, relative humidity, carbon dioxide concentration, freedom from pests and diseases, soil moisture content, light.
Make sure you use the term ‘relative humidity’ if you are choosing that as a factor, and don’t just say ‘humidity’.
For part b), it is important to take note of the words in bold in the question. Make it clear which environmental factors you are describing the effects of by writing each as a heading. The examiners’ comments suggest the following descriptions:
Air temperature - Low air temperatures will slow down growth and photosynthesis. More extreme low temperatures can cause frost damage. Temperatures that are too high will also reduce the rate of growth.
Relative humidity – High relative humidity can increase the incidence of fungal problems. Water and nutrient uptake can also be reduced. Low relative humidity will increase the rate at which plants dry out.
Quite a bit of information is required for a question that asks you to ‘describe’.
The answers for part c) should be set out clearly in a similar way. The examiners’ comments suggest the following as a suitable answer:
Air temperature – Can be controlled by using a combination of heating during the winter months to maintain an optimum temperature and the use of ventilation or damping down during the summer to lower the temperature.
Relative humidity - Can be controlled by providing ventilation to lower the relative humidity or by raising the temperature. Relative humidity can be raised by damping down the floors inside the protected structure or by reducing the air flow.