What controls how much a crop yields, and what are the arguments for and against GM crops?
The key factors affecting crop yield such as weather, soils, crop rotation, pests and diseases, the meaning of genetically modified crops, the advantages and disadvantages of widespread GM crop use, and the purpose of a seasonal crop management plan.
A focused CCEA GCSE Agriculture and Land Use answer on crop yield and GM crops, covering the factors affecting crop yield, the meaning of genetically modified crops, the advantages and disadvantages of GM crops, and the purpose of a seasonal crop management plan.
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What this dot point is asking
CCEA wants you to describe the factors that affect crop yield, define genetically modified (GM) crops, weigh up the advantages and disadvantages of widespread GM use, and explain the purpose of a seasonal (spring, summer, autumn, winter) crop management plan.
Factors affecting crop yield
Some factors (weather) cannot be controlled; others (soil fertility, rotation, pest, disease and weed control) can be managed to protect the yield.
Crop rotation
Rotation raises yields because it:
- Breaks the life cycles of pests and diseases that build up when one crop is grown again and again.
- Balances nutrient demand, as different crops use different nutrients, and a legume in the rotation adds nitrogen.
- Helps control weeds associated with a particular crop.
GM crops
- Advantages. Higher yields; resistance to pests and diseases (less spraying); tolerance of weedkillers, drought or poor soils; improved quality or nutrition. This can help feed a growing population and cut costs.
- Disadvantages. Concerns over possible health and environmental effects and biodiversity (genes spreading to wild plants); dependence on seed companies and buying new seed each year; and ethical objections from some consumers.
The seasonal management plan
A management plan organises the year's work by season so each job is done at the right time:
- Spring - prepare seedbeds, sow seeds, apply fertiliser.
- Summer - control weeds, pests and diseases; irrigate if needed.
- Autumn - harvest, store the crop, prepare ground for the next crop.
- Winter - maintain machinery, plan and order seed, carry out repairs.
The purpose is to make sure tasks happen at the correct time for a healthy, high-yielding crop.
Examples in context
Example 1. Rotating potatoes with cereals. A farmer follows potatoes with a cereal the next year rather than growing potatoes again. This breaks the cycle of potato pests and diseases (such as eelworm and blight build-up), rests the soil from the heavy demands of potatoes, and helps keep yields high without relying only on chemicals.
Example 2. Bt maize as a GM crop. Some maize has been genetically modified to make a natural insecticide (Bt) so it resists insect pests. The advantage is a higher yield with less insecticide spraying; the concerns are possible effects on non-pest insects and biodiversity and farmers' dependence on the seed company, which is why GM use is tightly regulated.
Try this
Q1. Name four factors that affect crop yield. [4 marks]
- Cue. Weather, soils, crop rotation, pests and diseases, and weeds (any four).
Q2. Give one advantage of GM crops. [1 mark]
- Cue. Higher yield, pest or disease resistance, tolerance of harsh conditions, or improved quality (any one).
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA Unit 1 style4 marksDescribe four factors that affect crop yield and explain how crop rotation can help.Show worked answer →
Three marks for factors and one for the crop rotation explanation.
Factors affecting crop yield include the weather (temperature, rainfall and sunlight), the soil (its type, fertility and drainage), pests and diseases that damage the crop, and weed competition. Crop rotation is another factor a farmer can control.
Crop rotation means growing different crops in a field in successive years rather than the same crop repeatedly. It helps because it breaks the life cycles of pests and diseases that build up under one crop, it balances the demand on soil nutrients (especially if a legume is included to add nitrogen), and it helps control weeds. This keeps the soil healthier and yields higher.
Markers reward correctly named factors plus a clear benefit of rotation (breaking pest and disease cycles, maintaining nutrients, controlling weeds).
CCEA Unit 1 style6 marksDefine genetically modified (GM) crops and discuss the advantages and disadvantages of their widespread use.Show worked answer →
One mark for the definition and the rest for balanced discussion.
Definition: GM crops are crops whose genes have been altered, usually by adding a gene from another organism, to give them a useful new characteristic.
Advantages: GM crops can be made to give higher yields, to resist pests and diseases (reducing the need for chemicals), to tolerate weedkillers, drought or poor soils, and to improve quality or nutrition. This can help feed a growing world population and lower costs.
Disadvantages: there are concerns about possible long-term effects on health, the environment and biodiversity (for example genes spreading to wild plants); farmers may become dependent on the companies that own the seed and have to buy new seed each year; and some consumers object to GM food on ethical grounds.
A strong answer links this to rising food demand and gives a balanced view. Markers reward the definition, several advantages and several disadvantages.
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