Answer: You've chosen an interesting experiment for your Science Fair Project. Different types of plants do best at different soil pH?s. (Soil pH tells you how much acid there is in the soil.) The more acid there is, the lower the pH will be. When a plant has a specific pH tolerance (blueberries, for instance), and you change the soil's pH, the nutrients the plant needs will be bound up and not available to the plant. So, changing the plant's ideal soil pH by adding an acidic acid or adding salt will result in poor plant growth because necessary nutrients will not be available to the roots.
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