What is the primary cause of nutrient runoff in agriculture?

Excessive fertilizer application is the primary cause of nutrient runoff in agriculture because it leads to an oversupply of nutrients, especially nitrogen and phosphorus, which can exceed the plants’ uptake ability. When heavy rains or irrigation occurs, these nutrients can leach into water systems, resulting in runoff that can contaminate nearby rivers, lakes, and groundwater.

Fertilizers are designed to provide essential nutrients for plants, but when applied in excess—whether due to over-application, miscalculation, or not accounting for soil nutrient levels—they do not all get absorbed by the plants. The surplus can accumulate in the soil, and during precipitation events, this excess is readily washed away. This runoff not only affects local water quality but can also lead to issues such as algal blooms, which can deplete oxygen in water bodies and harm aquatic life.

In contrast, practices like crop rotation and water conservation have been shown to mitigate nutrient loss and improve soil health, thus reducing the likelihood of runoff. Soil erosion, while a significant concern, generally contributes to nutrient loss through the physical removal of topsoil rather than through soluble nutrient runoff caused by fertilizer application.