Why is phosphorus regulated in fertilizer applications?

Phosphorus is regulated in fertilizer applications primarily because of its significant impact on freshwater quality. When phosphorus enters water bodies, often due to runoff from agricultural practices, it can lead to nutrient pollution. This pollution can result in excessive algal blooms, which deplete oxygen in the water and harm aquatic life. Monitoring and regulating phosphorus application helps mitigate these adverse environmental effects and protect water quality.

While phosphorus does have roles in enhancing soil structure, promoting plant growth, and even in pest control to some degree, none of these justifications align with the specific environmental concerns that necessitate regulation. Therefore, the focus on freshwater quality is the primary reason for the regulation of phosphorus in fertilizers.