In soil science, what does pH measure?

• A. Soil moisture content.
• B. Soil temperature.
• C. Electrical conductivity.
• D. The concentration of hydrogen ions, indicating acidity or basicity.

Answer: (D)

pH measures the concentration of hydrogen ions, indicating whether the soil is acidic or basic (alkaline). The scale is logarithmic, so small changes in pH reflect large changes in hydrogen ion activity, which directly influences nutrient availability and microbial activity in the soil. This is why pH is crucial for plant growth: at different pH levels, certain nutrients become more soluble and accessible, while others may become locked up or toxic. The other options describe different soil properties—moisture content, temperature, and electrical conductivity—each measuring something distinct from hydrogen ion activity.