At what pH level is phosphorus most available to plants?

Phosphorus availability to plants is significantly influenced by soil pH, and it is generally most available around a neutral to slightly alkaline pH range. The correct choice, which is a pH of 6.5, aligns with research and agronomic practices indicating that phosphorus is optimally available in the soil when the pH is close to this level.

At a pH level of approximately 6.5, phosphorus remains in a form that plants can easily absorb. As the pH begins to drift lower than this figure, phosphorus tends to bind with iron and aluminum, creating less availability for plant uptake. Conversely, when pH levels exceed 7, phosphorus can react with calcium, leading to the formation of less soluble compounds. Therefore, the pH of 6.5 strikes a balance that promotes the highest availability of phosphorus, making it the ideal condition for plant nutrition.

Understanding these soil chemistry principles helps in soil management practices, ensuring that phosphorus levels are maintained for optimal plant growth and crop yields.