What is pH?
Acidic, neutral and alkaline/basic are terms commonly used to describe pH. A measure of the concentration of hydrogen ions (H+) in a system, pH is described using a negative-logarithmic scale. This means that for each whole number step down on the pH scale there are ten times more hydrogen ions, or “acidity,” than the previous step. Neutral pH is 7, while the neutral pH range is generally thought to be between 6 and 8. Alkaline or high pH values are above 8, while acidic or low pH conditions are typically considered to be below 6. Figure 1 shows pH values for common substances from battery acid to lye.
pH in the Soil
In soil, pH is known as a master variable because it influences almost every process in the soil system. The health of crops and other soil life, the availability of nutrients, and the activity of pesticides are all affected by pH . Generally, soil pH below 5 is considered to be very low and extremely acidic for many agricultural crops.
A pH too far from neutral, either above (alkaline) or below (acidic), will make essential nutrients less available to plants. Figure 2 shows how pH affects nutrient availability in soil.