As the human population increases, there is a need to produce more food by more intensive farming. Increased food production has been achieved by:
- artificial selection for improved genetic varieties
- chemical fertilisers and pesticides
- biotechnology
- improved farming practices
- removing hedgerow and woodland
- monoculture - planting cereal crops in fields
- draining marsh and wetlands
- filling in ponds
- overgrazing of land
- use of pesticides and inorganic fertilisers
- escape of effluent from silage stores and slurry tanks into water courses
- absence of crop rotation
- lack of intercropping or undersowing