What is the primary concern of applying fertilizers immediately before rainfall?

The primary concern of applying fertilizers immediately before rainfall is the potential for nutrient loss through runoff. When fertilizers are applied to the soil surface before heavy rain, the excess water can wash away the applied nutrients, leading to loss from the intended area. This runoff can carry the nutrients into nearby water bodies, contributing to issues such as eutrophication, where algae bloom due to the excess nutrients, leading to reduced oxygen levels and harm to aquatic life.

Applying fertilizers at the right time is crucial for their effectiveness and for environmental protection. By understanding that rainfall can move nutrients away from the intended site, it becomes clear why it's important to time fertilizer applications to avoid heavy rain events. Other considerations, such as soil pH, moisture levels, and pest populations, may be relevant in different contexts, but the immediate concern with rain and fertilizers is the risk of nutrient runoff.