TREVOR CLIFFORD PHOTOGRAPHY / SCIENCE PHOTO LIBRARY TREVOR CLIFFORD PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Soil pH meter in a plant pot. A pH meter shows the alkalinity or acidity of a substance. Farmers and gardeners use these meters to assess a soil's suitability for different plants. A probe placed in the soil measures the amount of free hydrogen ions present, giving a value on the pH scale. A pH of 7 is neutral, above 7 is alkali and below 7 is acid. This meter displays a pH of just below 7, meaning that this is a mildly acid soil.
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