Yes I saw that, but in an Irish or Scots context, I understand that fertile land (here I'm talking about the Gaeltachtaí and the Highlands and Islands) tends to be called machaire - that is to say relatively flat and without too many stones and rocks in it, as opposed to the mountain sides overlooking it, and it's usually near the sea, so it would be sandy soil to which the crofters add seaweed. So would it be black ? Bríd Mhór would know more about it than I would. Perhaps black earth means something else apart from what they have in Ukraine.

Of course there's peaty soil, which is used in other countries for improving the soil in a garden, but in Ireland, isn't peat used for fuel rather than for anything else?

There's a townland in Moyrus near Carna anglicized as "Dooyeher", logainm.ie calls it Dumhaigh Ithir, but it is called Dubhithir in Irish, too.

Sandy or black earth ... strange.

The soil in Conamara is mostly the black peaty kind. Unless, like you said Franc, you are near the sea and it's sandy soil.
Yeah "machaire" is a large level field, mostly on the other side of Galway, not naturally occurring in Conamara.

I know what you mean. In some Conamara dialects "dubh" is pronounced as "du" (although still written as dubh), like in pronunciation of "dughorm"-without an accent (dark blue).
Personally I pronounce "dubh" as DUV.

dubhealaín - I've not heard that word spoken so I'm not sure how to pronounce it. I'd go with DUV AHLUEN