pH, SOIL ACIDITY, AND PLANT GROWTH pH, Soil Acidity, and Plant Growth

The reason for these questions lies in the fact that the pH, or degree of acidity of the soil, often is a symptom of some disorder in the chemical condition of the soil as it relates to plant nutrition. A measurement of soil acidity or alkalinity is like a doctor's measurement of a patient's temperature. It reveals that something naay be wrong but it does not tell the exact nature of the trouble. The acidity or alkalinity of every water solution or mixture of soil and water is determined by its content of hydrogen ions and hydroxyl ions. Water molecules break up, or in chemical language, ionize, into two parts—hydrogen ions and hydroxyl ions. When there are more hydrogen ions than hydroxyl ions, the solution is said to be acid. If there are more hydroxyl ions than hydrogen ions, the solution is alkaline (or basic). Solutions with equal numbers of hydrogen and hydroxyl ions are called neutral. Only a very small percentage of the water molecules present are broken up into hydrogen and hydroxyl ions at any one time. If one attempts to express the concentration of these ions in conventional chemical ways, some cumbersome decimal fractions result. In order to avoid these cumbersome 67