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C.6 Nitrogen and phosphorus cycles

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Description

Nature of science:
Assessing risks and benefits of scientific research—agricultural practices can disrupt the phosphorus cycle. (4.8)
Understandings:
  • Nitrogen-fixing bacteria convert atmospheric nitrogen to ammonia.
  • Rhizobium associates with roots in a mutualistic relationship.
  • In the absence of oxygen denitrifying bacteria reduce nitrate in the soil.
  • Phosphorus can be added to the phosphorus cycle by application of fertilizer or removed by the harvesting of agricultural crops.
  • The rate of turnover in the phosphorus cycle is much lower than the nitrogen cycle.
  • Availability of phosphate may become limiting to agriculture in the future.
  • Leaching of mineral nutrients from agricultural land into rivers causes eutrophication and leads to increased biochemical oxygen demand.
Applications and skills:
  • Application: The impact of waterlogging on the nitrogen cycle.
  • Application: Insectivorous plants as an adaptation for low nitrogen availability in waterlogged soils.
  • Skill: Drawing and labelling a diagram of the nitrogen cycle.
  • Skill: Assess the nutrient content of a soil sample.
Utilization:
  • Crop rotations allow the renewal of soil nutrients by allowing an area to remain “fallow”.

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