C.6 Nitrogen and phosphorus cycles

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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