Why does water poured onto already moist potting soil soak in faster than water poured onto completely dry potting soil?

Question

Why does water poured onto already moist potting soil soak in faster than water poured onto completely dry potting soil?

In: Earth Science

Answer 1

When the soil dries completely there are hydrophobic residues on the surface that prevent the water from being absorbed until the surface tension is broken.

ELI5-er:
When the soil dries completely, waxes and oils in the soil protect the surface.

Kind of like the way it is hard to wet a new towel.

Source: asked this exact question in hydrology class once.