Hiya..I hope this doesn't bring up more questions than answers as I am too trying to work out what the hell happened to half of my crop of Parsnips. Exactly half the drill was exactly as you describe & half were great...but from above they all looked the same.
If you don't wish to read through my rambling
- I'd sum up with: go for loose soil but try 1/2 1/2 to see for yourself.
Last season was the first on my plot. I put in 1 drill across the whole plot for the Parsnips. The soil was even in condition when I got it & it was dug through & prepared the same. All the other conditions were even along the drill too but to the 1 side of them we planted 1/2 the plot with Climbing Beans & 1/2 with peas & Sweet Corn.
The peas were small crop & didn't do so well (as I recon they were neglected early on in their fruiting when we went on holiday) & so they were more or less left alone - this is the 1/2 corresponding to where the parsnips did well...there's still 2 left this week.
By the time the beans grew to a good size they were very close to the parsnips (a true beginners mistake). It ended up to be a rampant crop of beans & so we tended them daily (we watered them in the middle of the frame & so I cannot say whether the watering reall effected the parsnips or not). The parsnips got knocked about a bit but more importantly it meant that the soil was greatly trodden down all around them. This is the 1/2 that did badly.
..oh yea..& I've just remembered that the same issue was brought up on BBC radio 4's gardeners quetion time in the last month - you'll have to try BBC's I player to get their answers as I didn't get to listen to them !
I hope this helps some.