What soil test result indicates lime is needed, and how is lime requirement determined?

• A. High pH above 7.5
• B. pH around 7.0
• C. pH below 5.5
• D. Low pH (below about 5.5–6.0) and lime requirement is determined by buffering tests or lime requirement curves

Answer: (D)

Low soil pH means lime is needed because acidic conditions reduce nutrient availability and soil biology activity. But you can’t rely on pH alone to know how much lime to apply, since different soils resist pH changes to different extents. That’s why the lime requirement is determined with buffering tests or lime requirement curves. A buffering test simulates how much lime is needed to move the soil pH to a target level by measuring the soil’s resistance to pH change. Lime requirement curves use the soil’s properties (like texture and organic matter) and the current pH to estimate the amount of lime required to reach the desired pH for the crop. The result is given as a rate, typically tons of lime per acre or per hectare.