Mulch will help, as will using a soaker hose under the mulch.

Roly-polys do not leave castings behind. You are probably seeing what ants dig out.

A bit of baby shampoo or dish detergent in water (1 tsp to a 1 gallon watering can) sprinkled slowly over the area until the dirt starts to get wet (a gallon for every square yard is not too much), followed by laying down the soaker hose and adding mulch, then watering regularly will fix it.

I do have mulch, which is why I have so many woodlice.

The fine dark spheres which make up the layer are their poop. They often practice coprophagy to recover the copper in their poos. In order to do this, they have to poop. They also can help remove heavy metals in soil, but very slowly and over a very long time!

I am certain it is not from ants. It is not soil and I would have to have A LOT of ants to make this layer.

From what I have read, detergents are not recommended, but rather real soaps. Or a concoction involving flat beer and spit. Yeech! The spit is for the enzymes. I could purchase a product ready made, but wanted to try soap.

I'm guessing Murphy's oil soap would be ok, but wanted to see if anyone knew for certain.

EWWWW! I would not use Murphy's near any of my food crops.

You can use Dawn dishwasher soap, just don't overdo it.

I'm having the same problem (hydrophobic soil) in certain areas. Seems like where I've let euc leaves decompose, the situation is worse. Hence, I won't be composting euc leaves anymore.

One thing that helps is to not let the soil dry out too much. If you let it get bone-dry, it's a battle to re-wet the soil.

There are commercial ag wetting agents out there. I haven't researched using them so far.

I did a LOT of research and some say yes on the soap, others say no. I think i'll try it.
zackey , soap is not ewww, unless you are getting your mouth washed out with it!

It can be a benefit when used sparingly. At the risk of being redundant, don't overdo it. And don't use a soap that contains any kind of additives. Keep it as plain and simple as possible.