Literally, pH stands for “potential of hydrogen” and is the term used by soil scientists to represent the hydrogen ion concentration in a soil sample. The relative alkalinity-acidity is commonly expressed in terms of the symbol pH. The neutral point in the scale is 7: soil testing below 7 is said to be acidic; soil testing above pH 7 is alkaline. The pH values are based on logarithms with a base of ten. Thus, a soil testing pH 5 is ten times as acidic as soil testing pH 5; while a soil testing pH 4 is one hundred times as acidic as soil testing pH 6.