Phosphorus is never readily soluble in the soil but is most available in soil with a pH range centered around 6.5. Extremely and strongly acid soils (pH 4.0-5.0) can have high concentrations of ...

Acidifying processes rarely affect the pH of calcareous soils, except occasionally in the top few centimetres of undisturbed soil. Failing to correct soil acidity can result in losses to crop yield ...

then comparing the results to a chart. Depending on the type of kit, there may be other steps involved. "Soil pH testing kits ...

Every plant requires a specific soil pH range within which it can best absorb ... then comparing its changed color to a chart. Similarly, test strips change color when dipped into a mixture ...