Posted: 06/04/2014 at 10:25
I don't know the scientific answer to this - hopefully someone will come along who does.
However, if they don't, my instinct is to cultivate the soil to a good spade's depth, leaving it for a couple of weeks for the weather and fresh air to work on it and birds to have a good scratch about.
If the soil doesn't appear or smell unpleasant after that then I'd dig in a good layer of well rotted farm yard manure and get on with gardening. However I think in the first year I'd not grow salad or root crops - I'd concentrate on beans, peas and brassicas.
If your're not happy with the soil then instead of planting veg for the first season, I think I'd sow a green manure that you dig into the soil later in the season - then when that's been done you could plant some winter cropping brassica plants bought from the GC and sow some winter-hardy broad beans to crop in the following spring.
Then next spring I'd stop worrying and get on and enjoy your veg patch.