Which crop nutrient is most likely to run off and cause water quality issues?

Phosphorus is the nutrient most likely to run off into water bodies and contribute to water quality issues. This is primarily due to its role in promoting algal blooms when it enters aquatic environments. When excess phosphorus is present, often from agricultural runoff, it can lead to eutrophication, where nutrient overload stimulates the rapid growth of algae. This can deplete oxygen levels in the water, harming aquatic life and disrupting ecosystems.

In comparison, while nitrogen can also contribute to similar water quality problems, its behavior in water systems is different. Nitrogen can leach into groundwater rather than run off into surface waters. Potassium and calcium are less frequently associated with water quality issues linked to runoff. They do not typically contribute to algal blooms in the way phosphorus does, making phosphorus the primary concern for water quality stemming from agricultural practices.