Don't hold me to it as gospel, but in checking on my resources, I came up with around 500 to 800 SF per bird per year.
Here is yet another source that says 100 SF per bird.
http://poultryone.com/articles/chickenmanure-html
So without much effort, you can find published resources that vary as much as 8X. Ouch.
Note the % of nutrients the poultryone folks use. the N-P-K values of 1.8%-1.5%-.8%........I found one source that suggested at least double those values. The old school rule of thumb was 50 birds per acre on something like grass sod or grain fields. That equates to about 875 SF per bird. That sounds like a lot of land, and it is.
The tricky part to doing these calculation is how much manure is actually in a pound of "litter" and what is the water content? Most references don't really say. You get numbers like 1,000 laying hens will produce 20 tons per year of "litter"? Litter or manure? Considering the source, I'm thinking it was manure and that would be manure stockpiled in the end of a commercial laying house. Manure of course contains both liquid urine and solid feces and it comes out together as one. So is this dry or wet litter? Fresh wet litter will be nearly double the weight of stockpiled litter that has been allowed to dry. That may explain the differences in % per pound? Wet or dry? It does make a difference.
Manure is widely thought to be high in N, but a lot of that quickly gets converted to ammonia gas and blows off into the air. But what is left and what quickly gets out of hand is the phosphorous (P) and a lessor extent potassium (K). So the "crops" planted need to be heavy feeders of those two. Composting is going to help shed a lot of the excess N, but not the other two minerals. Over time, what looked like a good thing early on starts to become a problem as excess starts to build up. Long term, the put and take have to reach an equalibrium or things start getting toxic. And again, it is not always the Nitrogen that gets going too hot.
For yet another reference, here is a guide bulletin from U of Missouri (lots of broilers and turkeys in Missouri)
http://extension.missouri.edu/p/WQ203
When you get down to the part about how many pounds of broilers and 2 acres of land........when I convert pounds of birds to layers, at 5 pounds per bird, I come in around 435 SF per bird.
If you were one of the big boys, with thousands of birds to deal with and the need for a CAFO permit, this is how much land area the State of Missouri would want you to have lined up with spreading rights. So that might be a good place to start.