Cengage Horticulture Exam 1 Practice

Soil pH determines how nutrients dissolve in soil water and how readily roots can take them up. When pH shifts, the chemical form of many nutrients changes, altering their solubility. In acidic soils, metals like iron, manganese, and zinc become more soluble, while phosphorus can become less available because it binds with aluminum or calcium depending on the exact pH. In alkaline soils, several micronutrients become less soluble and harder for roots to absorb.

Because plants only take up nutrients dissolved in the soil solution, the right pH range helps keep essential elements in a form that roots can access. For example, phosphorus tends to be most available around neutral to slightly acidic pH, while iron and other micronutrients become scarce if the soil is too alkaline. This is the core reason why pH is tied so closely to nutrient availability.

Other soil properties described by the distractors—such as texture affecting pore space and water retention, or temperature and climate influencing root growth—are not driven by pH in the same direct way. So the best answer links pH to how soluble nutrients are and how easily roots can absorb them, which is exactly what determines nutrient availability.