hardpan
/ˈhɑrdˌpæn/
noun
- A hard, dense layer of soil or clay beneath the surface that water and plant roots cannot easily pass through.
- In dry regions, hardpan can prevent rainwater from soaking into the ground.
- Construction crews often need special equipment to dig through hardpan.
- The gardener had to break up the hardpan to improve drainage in the flower bed.
Synonyms