I agree with Wexflyer that this could be a somewhat muddled assessment, without a scientific basis. I don't know about Ireland, but in GB there is now a difference between Land Utilisation and Land Use Capability which emerged during the 20th cent. in sets of maps overprinted on OS base maps. In the 19th cent. the difference was probably somewhat subjective.
Quality of Land implies Land Use Capability, i.e. what the land could be used for, rather than what it is actually being used for, which would be affected by agricultural markets. In the UK during the inter-war depression large areas of arable land were "put down to grass" i.e. pasture, which was reversed by the "plough-up campaign" at the beginning of WW2.
In enclosure awards the lawyers typically use as many words as possible saying "commons, moors, heaths and wastes". I am uncertain what they actually mean by these words, but I suspect they were recognised by the types of natural vegetation growing there, determined by soil-type and drainage. The word "moor" was widely used in lowland areas, and still persists in place-names. At enclosure, thousands of acres were drained, ploughed and turned into arable, though probably not of the best quality.
