Which statement about soil pH and nutrient availability is true?

• A. As pH increases, availability of most nutrients increases.
• B. As pH decreases, all nutrients become unavailable.
• C. Soil pH affects only microbial activity, not nutrient availability.
• D. Soil pH affects nutrient solubility; some nutrients are more available at certain pH ranges.

Answer: (D)

Soil pH shapes how nutrients exist in the soil and how easily plant roots can take them up. This is why the statement about pH affecting nutrient solubility and noting that some nutrients are more available at certain pH ranges is true. Different nutrients have different optimum pH windows because their chemical forms change with acidity or alkalinity, which changes whether they stay dissolved in soil solution or become bound to soil particles. For example, micronutrients like iron and manganese are more soluble in acidic conditions, so they are more available there, while phosphorus tends to form insoluble compounds at both very low and very high pH, making it less available outside its preferred range around neutral to slightly acidic soil. In contrast, some nutrients remain relatively available across a broad range, but none are universally more available as pH rises for all nutrients. The other statements don’t fit because pH doesn’t universally increase all nutrient availability, nor does it render every nutrient unavailable when it falls, and it indeed affects nutrient availability, not just microbial activity.