Which statement about soil pH and nutrient solubility is true?

• A. All nutrients become soluble when pH is right.
• B. Ion exchange is not affected by pH.
• C. pH has no influence on micronutrient availability.
• D. Some nutrients may become insoluble and unavailable when pH is too high or too low.

Answer: (D)

Soil pH governs how nutrients dissolve and move in the soil water, and it also affects how strongly nutrients bind to soil particles. The true statement captures a fundamental reality: at very high or very low pH, some nutrients can become insoluble or get locked up in forms that plants cannot access.

For example, in strongly acidic soils, phosphorus often precipitates as compounds with aluminum or iron, making it less available even if you add more. On the other hand, iron and manganese tend to be more soluble in acidic conditions, which can lead to toxicity if they become too abundant. In alkaline soils, iron, manganese, zinc, and boron often become less available because they form insoluble compounds or bind to soil particles, while phosphorus can also become less available as calcium phosphates form.

This is why there isn’t one pH where all nutrients are perfectly available; each nutrient has its own patterns of availability across the pH spectrum, and extremes in pH can reduce the solubility and uptake of several essential nutrients.