Which instrument is used to determine soil temperature?

The soil thermometer is specifically designed to measure the temperature of the soil at various depths. This instrument typically features a long probe that allows it to be inserted into the soil, where it can accurately read the temperature without being affected by surface conditions. Knowing the soil temperature is crucial for various agricultural practices, as it can influence seed germination, plant growth, and microbial activity within the soil.

While other instruments listed have their own uses—such as the soil sample probe for taking samples, the hydrometer for measuring moisture content in solutions, and the thermocouple for various temperature measurement applications—the soil thermometer is specifically optimized for soil temperature measurement, making it the most suitable choice for this query.