describe how glasshouses and polythene tunnels can be used to increase the yield of certain crops
Glasshouse - allows plants to grow earlier in the year, and/or in places where they would not normally grow well
Provides warmth, light, carbon dioxide and water
Increases crop yield - best possible conditions for photosynthesis to take place
- Optimum temperature for photosynthesis (enzymes work efficiently // fastest rate of reaction)
- Allows constant temperature throughout the year // constant production
- Prevents loss of water vapour // constant supply of water
- Frost damage to seedlings avoided
- Warmed by burning of fossil fuels // increasing CO2 levels
Temperature
- Sunlight heats up the inside of the glasshouse
- Glass stops (most of) heat from escaping
- Electric/paraffin heaters can be used in cold weather
- Ventilator flaps can be opened to cool greenhouse
Light
- Glass lets in sunlight
- Artificial lighting can be used to grow plants if sunlight gets too low
- Blinds can shade out overly strong light
Temp+Light
- Solar radiation (initial source of energy) in the form of light, is let in through the glass into the glasshouse
- Light absorbed by surfaces inside the glasshouse (soil, wooden surfaces, plants)
- Surfaces reemit energy as heat
- Heat warms the air
- Temperature increases - creates a convection current inside the glasshouse
Carbon dioxide
- Growers can pump CO2 into glasshouses
- Paraffin heaters are used sometimes
- Increase both temperature and CO2 (paraffin burning => releases CO2)
Water
- Many glasshouses have automatic watering systems
- Sprinklers, humidifiers
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| Source: www.indiana.edu |
Polythene tunnels
- Allows light to pass through into the interior
- Used in less developed countries (cheaper)
- Adjustable and movable but less efficient and has less shelter for the plant
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| Source: www.thegardensuperstore.co.uk |
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