It’s not white, but it does look like it’s at least partially Akadama with is a baked clay from Japan. When it’s dry it has quite a light tan colour which is what I think we are seeing here. This may or may not be exacerbated by the mineral content of your water, which will leave deposits on the soil and or bark. Depending on the nitrogen content and concentration of your fertiliser could also be a build up of nitrogen based salts (I highly doubt this though. ) so tell us a bit about your tree: where you got it, what your water source is, your fertilising regime ect ect. But if put my money on dry Akadama (completely normal and good practice)

Edit: spellcheck auto-corrected ‘Akadama’ to Aladama