Shallow soil, freshly manured soil, lack of water, hard clay soil, stoney soil. Take your pick!

a grower of show parsnips told me that the tilth has to be extremely fine. otherwise the root does not go down well and splits. some of ours have been fine this winter others have split.

Parsnips can be real bu****s to grow and any or all of the reasons that owdboggy gave will cause the symptoms you describe. If your soil is shallow or hard etc how about filling a container (45 gallon drum etc.) with good quality soil and planting your seeds into this? Make sure it is finely riddled first and doesn't get compacted!