Here's why:
* Fine particles: Clay soil has very fine particles that pack tightly together.
* High water content: When wet, clay soil holds a lot of water, making it soft and pliable.
* Shrink-swell: When clay dries, the water evaporates, and the particles shrink and pack even tighter. This results in a very dense, hard, almost rock-like consistency.
Other soil types that can harden when dry:
* Loam: While not as dramatic as clay, loam can become firm and difficult to work when dry, especially if it has a high clay content.
* Silt: Silt can also become hard when dry, but usually not as hard as clay.
Important note: The degree to which soil hardens when dry depends on the specific type of clay, the amount of organic matter present, and the climate conditions.
