Measuring Soil pH

• No matter how you approach the topic, you will need some way to collect data on soil pH. Electronic pH meters are available from greenhouses and garden centers, and they will allow you to take readings quickly and accurately. This can help to build up a database for charts and graphs. You can also purchase liquid pH test kits, which change color to reflect the pH of soil that is mixed with the test base. Having multiple vials of colored liquid reflecting the pH of various soil samples is an effective visual aid. You can also make your own pH testing base by boiling the juice out of red cabbage, which is a natural pH indicator.
  
  

Soil Samples

• A well-designed science experiment requires a broad range of data. You can take soil samples from various places in and around your town to demonstrate the different pH levels present even on a local basis. What might cause the pH levels to be different in various locations? Are these differences likely to be man-made or natural? Is the pH balance reflected in the appearance and consistency of the soil? How would the pH balance of these soils affect rainwater that soaks into them?
  
  

Effects on Plant Life

• Plants tend to have specific pH needs. Most lawns thrive in soil with a neutral pH balance, while flowers such as azaleas and hydrangeas prefer acidic soil. Many desert plants such as cacti and rock plants are adapted to more alkaline soils. Is the pH balance of the soil you sampled reflected in the type or health of plants growing in the area? You can demonstrate the importance of soil alkalinity by growing plants in separate pots with high, neutral and low pH. A mix of acid-loving, neutral and alkaline-loving plants will be most effective in this sort of experiment.
  
  

Modifying Soil pH Balance

• As gardeners know, soil pH can be changed by adding substances such as lime or chalk to the topsoil. This can help certain plants thrive in areas where the natural soil pH balance runs counter to the plants' natural preference. Which substances work best to alter soil pH? What is it about the chemistry of these substances that make them good pH modifiers? Are there any unwanted side effects that could be caused by applying these substances to your yard or garden?