For a good study of Hardy and folk song, see C M Jackson-Houlston, Ballads, Songs and Snatches: The Appropriation of Folk Song and Popular Culture in British Nineteenth-Century Realist Prose (Aldershot: Ashgate Publishing, 1999), chapter 8 and appendix 2; and the article on which it was based, 'Thomas Hardy's Use of Traditional Song' in Nineteenth Century Literature, vol 44 no 3, December 1989, 301-334.