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This content is taken from the Lancaster University's online course, Soils: Introducing the World Beneath Our Feet. Join the course to learn more.

Skip to 0 minutes and 11 seconds You can purchase soil pH test kits online and from garden centres. They provide a rapid and relatively accurate method of measuring soil pH. Most kits require you to add soil to a vial together with a chemical, and leave it for the solution to change colour. You can then match it to a chart.

Skip to 0 minutes and 35 seconds You can also test pH using red cabbage. It’s less accurate, but it will give you an idea of pH. Take your head of red cabbage and finely chop it using a knife or a food processor. Bring a pan of water to the boil. Ideally, this should be distilled water, which is available from petrol stations. But if you don’t have access to it, tap or bottled water will suffice. Add the chopped red cabbage to the boiling water and remove it from the heat. Allow it to soak for about 10 minutes, and then drain the solid pieces out, leaving the purple juice.

Skip to 1 minute and 18 seconds Test the juice by putting some cabbage juice into two cups. And then, add vinegar, which is an acid, to one, and baking soda, which is basic, to the other. Acid should turn the solution pink. And the basic baking soda should turn it blue or green. Put a small amounts of cabbage juice in a clean cup, and add two teaspoons of soil. Wait 15 minutes, and then check the solution. Purple or violet is a pH near 7. Neutral. Pink means the soil is acidic, with a pH between 1 and 7. The more acid the soil is, the brighter the pink will be. Blue or green is a pH between 8 and 14. Alkaline.

Skip to 2 minutes and 11 seconds The brighter green the juice is, the more alkaline it is.

Practical activity - measuring soil pH

Soil acidification was highlighted in the previous video as a side effect of atmospheric nitrogen deposition. There are other acidifying pollutants in the atmosphere such as sulphur. In order to monitor the long-term effects of acidifying pollutants we commonly monitor soil pH.

The pH scale is used to measure how acidic or basic (or alkaline) a substance is. The scale goes from 0 which is the most acidic to 14 which is the most basic. Pure water is neutral with a pH of 7. Soils with a pH below 6 are considered acidic and above 8 are considered basic.

There are many factors aside from pollution that control the pH of a soil including the parent material, the plants that grown in it, and the moisture content. However, soil pH is not only important as a consequence of pollution but also for governing what plants can grow in it - a concept that will be familiar to gardeners.

This video describes two different ways that you can test your soil pH. You can use the transcript in the downloads section as a set of instructions.

Safety tips

  • Make sure your kitchen is safe and be aware of any young children that may wander in while you are carrying out this experiment
  • Make sure the pan of boiling water is placed steadily on the cooking surface, with handles pointing away so they can’t be knocked
  • Make sure you wash utensils thoroughly after use
  • Take care when chopping up the cabbage
  • Be careful if you get vinegar or baking powder on your hands – wash your hands and don’t touch your eyes

Please check our safety tips in the download section below.

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This video is from the free online course:

Soils: Introducing the World Beneath Our Feet

Lancaster University

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