tensiometer

/ˌtɛnsiˈɑmɪtər/
noun
  1. An instrument that measures the tension or surface tension of a liquid, or the moisture tension in soil.
    • Farmers use a tensiometer to check soil moisture and decide when to water crops.
    • The scientist used a tensiometer to measure the surface tension of the soap solution.
    • A tensiometer can help prevent overwatering by showing how dry the soil really is.