I let my chickens have access to my greenhouse all winter...
By the time that I kick them out, there is a sheet of solid poop in there.
I roll up the poop sheet and take that out... then I flood the soil at least twice (washes out lots of the salts and the ammonia etc.)
Then I plant transplants. If I put in a transplant with just a tiny bit of soil around it, it at times gets a bit burned, but soon recovers and grows well.
putting in transplants with a nice sized root ball of clean dirt works best.
After the seedlings have been in there for a couple of weeks.... probably mostly because of the continual watering... I can then direct seed without any trouble.
I also let my chickens have access to my garden in the off season. They do a wonderful job of killing all green things, digging up grubs, and fluffing up the soil. When it is time to plant, I kick them out and rake the dirt smooth.
In the vegetable garden, there is enough space, that there is no poop mat, and no problem with nitrogen burning plants or seedlings.