Protected cultivation using glasshouses and polytunnels and its economic importance, the factors that can be controlled in a greenhouse, the advantages and disadvantages of hydroponics for world food production, and the environmental and economic benefits of composting.

What this dot point is asking

CCEA wants you to explain protected cultivation (glasshouses and polytunnels) and why it matters economically, list the factors a grower controls in a greenhouse, weigh up hydroponics for world food production, and give the environmental and economic benefits of composting.

Protected cultivation

The problem protected cultivation solves is the short, cool and wet growing season in Northern Ireland, which limits how long outdoor crops can be grown. A glasshouse or polytunnel traps heat and shelters the crop, so growers can start earlier and finish later.

Factors controlled in a greenhouse

Inside a greenhouse the grower can control the conditions that affect growth:

• Temperature (using heaters and ventilation)
• Light (using extra lamps to extend day length)
• Water (using irrigation systems)
• Carbon dioxide (sometimes added to speed photosynthesis)
• Protection from wind, frost, pests and diseases

By removing limiting factors, plants grow faster, more reliably and with better quality, with fewer losses.

Why it is economically important

Protected cultivation lets a grower supply crops such as tomatoes, strawberries and salad leaves earlier than the open-field season, when prices are higher and demand is strong, and to satisfy market demand for a steady supply. The higher yield and quality, and the premium for early produce, make the extra cost of heating and structures worthwhile.

Hydroponics

Hydroponics matters for world food production because it can grow food where soil or land is poor.

• Advantages. It works where there is no good soil or little land (cities, dry regions); the grower controls the exact nutrients, giving fast growth and high yields; water is saved because it can be recirculated; and there are fewer soil-borne pests and diseases.
• Disadvantages. It is expensive to set up and run, needing pumps, tanks, and often artificial light and heat, so it uses a lot of energy; it needs skilled management because a system fault can quickly kill the whole crop; and it depends on a constant power supply.

Composting

Composting turns garden, food and farm waste into a dark, crumbly soil improver as decomposers break it down. Its benefits are both environmental and economic:

• Environmental: it recycles waste that would otherwise go to landfill (including household brown bin waste), reduces methane from landfill, and returns organic matter and nutrients to the soil.
• Economic: it provides a free or cheap soil improver, reducing spending on fertiliser, and councils save on landfill costs.

Examples in context

Example 1. Strawberries in polytunnels. A Northern Ireland fruit grower raises strawberries under polytunnels. The tunnels keep off the rain and wind, raise the temperature, and protect the fruit, so the crop ripens earlier and is cleaner and of higher quality, letting the grower supply supermarkets ahead of the main outdoor season.

Example 2. Lettuce grown hydroponically. A salad producer grows lettuce hydroponically in a controlled glasshouse. With roots fed a precise nutrient solution and recirculated water, the lettuce grows quickly and cleanly year-round on a small footprint, though the producer must pay for lighting, heating and skilled staff to run the system.

Try this

Q1. List four factors a grower can control in a greenhouse. [4 marks]

• Cue. Temperature, light, water, carbon dioxide and protection from pests (any four).

Q2. Give one environmental benefit of composting. [1 mark]

• Cue. It recycles waste away from landfill and returns organic matter and nutrients to the soil.