I believe it is a lack of root development at this stage of plant growth.  Wet conditions at planting compacted the area around the plant, from you press wheels.  Yes, lack of a clean soil caused the soil to be cool and wet, not a good combination for rapid plant growth. 

I believe that the good cover crop of vetch will benefit you later in the growing season by conserving your moisture.

Here in Nebraska those who plant winter wheat one year let it lie after harvest, use chemicals to keep the weeds down,  plant into the unworked stubble the next spring raise the highest yielding corn because of all the good mulch of wheat straw still remaining.  It does a great job of conserving moisture.  We some times can go 6 weeks with out any rain during the plants growth. 

Your plant roots have not yet reached that fertilizer you put out. 

Take you shovel  and carefully dig up some plants to see how much of a root it has.  Very little at this stage of growth. 

It should be fine in time.