What are slow-release fertilizers coated with?

Slow-release fertilizers are typically coated with sulfur. This coating serves a critical purpose by controlling the rate at which nutrients are released into the soil. The sulfur coating creates a barrier that delays the solubility of the fertilizer's nutrients, allowing plants to access them gradually over time instead of all at once. This steady release helps prevent nutrient leaching and ensures that plants receive a consistent supply of essential nutrients for an extended period.

In comparison to the other options, nitrogen, urea, and phosphorus are key nutrients commonly found in fertilizers, but they are not primarily used as the coating material for slow-release formulations. Instead, they serve as the actual nutrients that support plant growth and health. The coating material, such as sulfur, is what specifically aids in controlling how these nutrients are delivered to the plants.