Which statement about the effect of extreme soil pH on nutrient availability is true?

• A. All nutrients become more soluble at extreme pH.
• B. Some nutrients may become insoluble and unavailable when pH is too high or too low.
• C. Nutrient availability is unaffected by pH.
• D. Nutrients are always equally affected by pH changes.

Answer: (D)

Extreme soil pH changes the chemical forms and solubility of nutrients, so availability to roots swings as pH moves away from the optimal range. When pH is too high or too low, several essential nutrients can form insoluble compounds or become tightly bound to soil particles, making them unavailable for uptake. This is why the statement that some nutrients may become insoluble and unavailable at extreme pH levels is true: nutrient availability does not stay constant, and not all nutrients react the same way—some may become less available, some may become more available, and others may be unaffected, depending on their chemistry and the soil conditions. In practice, maintaining a soil pH in the appropriate range helps keep most nutrients in forms plants can absorb, which is why extreme pH is often associated with nutrient deficiencies.