Carrots & Parsnips

Has anyone used Root trainers to bring on parsnips??? Instead of loo rolls. My parsnips were awful last year - they were in sandy soil and sunshine in my garden, (well what sunshine there was).  The alternative site is clay soil for them in my allotment where weirdly my carrots do really well. When I tried parsnips in the allotment clay soil I got nothing at all!!!.  I do love a good parsnip.