There are other types of soil that can be more crumbly, but this is not the least. Because porous means something is full of tiny holes or openings, you can see that this is the right word to match it with! The least crumbly, or porous would only have a little crack. Good luck, and I hope this helped!
Also....
Clayey soil is the least porous.
Clayey soil is the least porous soil as the spaces between the molecules of the soil is less and water cannot pass through them.
