Soil acidity has a direct effect on the plant and is a major factor affecting nutrient availability to plants. Mclean, E.O . Soil pH and line requirements. In Methods of Soil Analysis , Part 2 . Chemical and Microbiological Properties .
Cups are capped after weighing to avoid moisture loss.
Using a repipet or graduated cylinder 30 mls deionized water is added to each cup, capped and shaken for a few seconds. The cap is removed to allow the solution to equilibrate with the atmosphere for at least 30 minutes. The pH meter is standardized at pH 7 and 4. While gently swirling the slurry the electrode is placed into the slurry. Between samples the electrode is rinsed with deionized water.