What does soil pH measure and how do field and lab measurements differ, and what is the typical target pH range for many rangeland plants?

• A. The pH measures moisture content of soil; field uses moisture probes; lab uses gravimetric methods; target around 8.0–9.0.
• B. The pH measures hydrogen ion activity; field uses a soil paste or electrode; lab uses extractants; target generally around pH 6.0–7.0 for many rangeland species.
• C. The pH measures total alkalinity; field uses litmus paper only; lab uses color indicators; target generally around pH 4.0–5.0.
• D. The pH measures salt concentration; field uses electrical conductivity; lab uses pH meters; target around 6.5–7.5.

Answer: (B)

Soil pH is a measure of hydrogen ion activity in the soil solution, which largely determines how available nutrients are to plants. The field reading is usually obtained by making a soil paste or using a portable pH probe, giving a quick sense of what the plants are experiencing in the field. This in-field measurement is convenient and reflects current moisture and temperature conditions but can be less precise due to environmental factors. In the lab, samples are treated with a standardized extractant to stabilize the measurement and better represent the soil’s exchangeable acidity, then measured with a calibrated pH meter. This approach is more reproducible and comparable across samples.

For many rangeland plants, a pH around 6.0 to 7.0 is typical and generally favorable, supporting a broad range of nutrient availability for grasses and forbs. Some species can tolerate slightly more acidic or alkaline conditions, but the near-neutral range is a common target for productive rangeland systems.