Which nutrient contributes significantly to the risk of water quality issues when overapplied?

Nitrogen is a nutrient that, when overapplied, poses a significant risk to water quality. This is primarily due to its high solubility and mobility in soil and water systems. When nitrogen levels exceed what plants can use, it can leach into groundwater or run off into surface water bodies. This process can lead to nutrient pollution, often resulting in harmful algal blooms that degrade water quality, harm aquatic ecosystems, and pose risks to human health.

In addition to its direct effects on water quality, nitrogen pollution also contributes to various environmental problems, including eutrophication and hypoxia in water bodies. These phenomena can lead to oxygen-depleted zones where aquatic life cannot thrive, negatively impacting both biodiversity and fisheries. This makes nitrogen management a crucial aspect of maintaining healthy water ecosystems.

The other nutrients listed do not have the same level of risk associated with overapplication in terms of water quality issues. Potassium, calcium, and sodium typically do not cause the same degree of environmental degradation related to water quality as nitrogen does. Therefore, the understanding of nitrogen's role in nutrient management is vital for protecting water resources and promoting sustainable agricultural practices.