Too much nitrogen?

Thanks for all of your posts!
 Nobody did too well with sprouts lasts year, i didnt grow any but others did and none of them were staked, nor did it look as though the ground was firmed a great deal.

I was gonna firm the brassica bed by walking on a plank ( ) then covering with some black polythene tightly on the surface, thinking that any rain we get will help firm it more. Ill let you all know how i get on !!

Totty