I know this is an odd one, but I know there is a special word that horticulturists use to describe soil that is so arid that it resists water. So, when it rains, the water initially rushes off of the soil rather than soaking in; counter intuitive to what you would expect. Please help me remember this word.
Hydrophobic soils repel water or absorb it weakly. The opposite term is hydrophilic.
Any soil can get so dry (so desiccated) that the normally hydrophilic particles turn to one another for their hydroxyl ions. It isn't wrong to call them hydrophobic while in that state, although it's an electrostatic condition rather than a soil-type, and can equally apply to clay or organic molecules in the soil. Where both are present it may involve both. This is what causes a potful of peaty compost that got really dry to be so hard to re-wet, and pretty much impermeable.