Soil pH - Soil Essentials: Managing Your Farm's Primary Asset - page 7

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Soil pH
Background
Soils are made up of varying quantities of sand, silt, clay and organic matter, both
living and dead. A soil with good structure allows water to move down the soil
profile, and even when a soil appears dry there is still some water in it. This water
contains dissolved chemicals that can cause the soil to be acid or alkaline. The
acidity or alkalinity level can change over time and will affect how well plants will
thrive in that soil.
What is the pH scale?
The unit of a scale used to measure the level of acidity or alkalinity of chemicals is
called pH. The unit pH relates to the number of hydrogen ions in a solution, and
ranges from pH 0 (most acid) to pH 14 (most alkaline), with pH 7 being neutral.
The pH range for most soils is between pH(w) 4 to pH(w) 10 (Figure 3).
Testing soil pH
There are two main laboratory techniques for measuring soil pH: one measures the
pH of soil mixed with water, and the other measures the pH of the soil in a calcium
chloride (CaCl 2 ) solution. It is important to bear in mind that laboratories may use
either or both of these testing methods, and that the figures obtained will differ
between methods.