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.

Answer 2

Wet soil clumps, creating gaps for the water to pour into.

When the soil dries it separates again and spreads out to create a broadly uniform layer (thanks, gravity!). That makes a barrier for the water.

Answer 3

I believe it has something to do with the path of least resistance. Like, it’s already wet and the water thats made it wet has been there done that while water in dry soil must find the pay of least resistance and go there do that.