Nitrogen and phosphorus cycles

Nature of science:

Assessing risks and benefits of scientific research—agricultural practices can disrupt the phosphorus cycle. (4.8)

• 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.

• Crop rotations allow the renewal of soil nutrients by allowing an area to remain “fallow”.