Soil is made up of various components which determine its properties. These include mineral particles (sand, silt and clay), organic matter (living and dead), air and water.
The water component is where pH is measured, where dissolved chemicals cause the soil to be acidic or alkaline. Soil pH is the measure of acidity or alkalinity in your soil.
pH has a strong control on the soils chemical environment. Having the correct pH is important for healthy plant growth.
Soil acidity and alkalinity are measured in units of pH. The pH scale is from 0 (most acid) to 14 (most alkaline) and a pH of 7 is neutral. pH is measured using a logarithmic scale, which means that for a pH decrease of one, the acidity increases by a factor of 10.
Most soils have pH values between 4.5 and 9.5. Soils with a pH value of 6.5 to 7.5 are referred to as neutral, while those with a pH less than 6.5 are acidic, and greater than 7.5 are alkaline.
Soil pH affects the amount of nutrients that are soluble in soil water, and therefore, the amount of nutrient available to plants. Some nutrients are more available under acid conditions while others are available under alkaline conditions. However, most mineral nutrients are readily available to plants when soil pH is near neutral.
It is a good idea to regularly test your soil pH, an approximate of soil pH can be made with a relatively inexpensive field test kit, and if done regularly it provides a good guide to soil pH.
For accurate testing, soil samples should be sent to a soil laboratory.
There are two different measures of pH commonly undertaken on laboratory soil testing. pH in water, and pH in calcium chloride (CaCl2)
- pH(CaCl2) is less variable across seasons- it is less influenced by soil salts and ions.
- pH(water) is standard on alkaline soils.
- pH(water) is generally more representative of conditions experienced by roots
- The big thing to remember is that pH(CaCl2) usually around a unit lower than pH(water)
Some soils in the South East are naturally acid, and others are naturally alkaline. There are some soils in the South East which are more prone to soils acidity than others. Underground water in the South East is naturally alkaline, and irrigated soil has a tendency to be alkaline.
Information on this page comes from the Australian Soil Health Knowledge Bank and Glenn Bailey, Rural Solutions SA.