pH in Deep Sandy Soil

Mallee Sand Soil pH Indicator

When analysing deep sandy soils, a good starting point is assessing the pH in different horizons in the profile. In the Mallee soils it is regularly seen, as expected, that there is an increase in pH going down through the profile. This can be readily indicated using a ‘do it yourself’ pH kit that you can purchase from most hardware stores.
It is a simple way to assess a fundamental soil variable which will influence how many other soil processes will operate.

As can be seen in a sandy soil from last week in the photo above, the top soil, picture on the right, is relatively acidic at roughly pH 5 with the next layer down, pictured left, being at approximately pH 7.

With pH working on a logarithmic scale, which means for every pH unit that is increased or decreased means 10 times increase or decrease in acidity. Therefore over a small depth the when the pH of the profile changes 2 units it is 100 times more alkaline or less acidic. This is such an important point as many soil samples are taken by an operator who has unknowingly mixed different soil horizons.

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