Which soil property is most strongly linked to nutrient availability due to chemical changes in nutrients?

• A. Organic matter
• B. pH
• C. Texture
• D. Structure

Answer: (B)

Nutrient availability in soils is controlled mostly by pH because the acidity or alkalinity of the soil changes the chemical form of nutrients. The pH determines whether nutrients dissolve into the soil solution or precipitate as insoluble minerals, and it also affects how strongly nutrients are held or released from soil particle surfaces. For example, in acidic soils some nutrients become more soluble and others may release aluminum ions that can bind or toxicize, while phosphorus tends to form less soluble compounds with calcium, iron, or aluminum depending on the pH. In alkaline soils, many micronutrients such as iron, manganese, zinc, and copper become less available because they precipitate as hydroxides or carbonates. Organic matter and mineral texture influence how much nutrient can be held or released, but the direct, dominant control over the chemical forms and solubility of nutrients—and thus their availability to plants—comes from soil pH.