True or False: Clay soil expands when wet and shrinks when dried.

Clay soil is indeed known for its ability to change volume in response to moisture content. When clay soil becomes wet, the particles absorb water, causing them to expand. This property can lead to an increase in volume, which is particularly relevant in construction and landscaping as it can affect the stability of structures and the growth of plants.

Conversely, when the clay soil dries out, it loses moisture and contracts. This shrinking can create cracks and gaps, leading to further instability if not properly managed. Understanding this behavior of clay soil is crucial for anyone involved in building or gardening, as it directly impacts how water management, foundation design, and plant selection need to be approached.

The other choices do not accurately encapsulate the fundamental nature of clay soil. While humidity and regional differences can influence soil behavior, they do not change the basic property of clay to expand when wet and shrink when dried. This characteristic is intrinsic to clay's composition, regardless of the climate or location.