What is soil pH?
The chemical environment of the soil can be acid, neutral or alkaline. The movement of strongly acid balancing ions such as sulphate or nitrate through the soil generates excess acidity and the accumulation of strongly basic ions (i.e. calcium and sodium) generates alkalinity.
Soil pH indicates the net acidity or alkalinity of a soil. Specifically it measures the concentration of hydrogen ions in soil solution on a logarithmic scale that goes from 1 (extremely acid) to 14 (extremely alkaline). Acidity developes as the concentration of hydrogen ions increases in soil and as a result soil pH declines. The pH can vary significantly between different soil layers. For example sandy topsoil with a pH of 5 may have clay subsoil with a pH of 8 or sandy subsoil where pH continues to decline. This suggests it is important to measure soil pH in different horizons of the soil to ensure appropriate management.