Nitrogen is required for amino acid synthesis. Plants can use NO
3, "fixed" nitrogen efficiently, they can use ammonium NH
4 and ammonium salts slightly less efficiently. Uric acid in chicken manure along with some protein degradation products are converted to ammonia/ammonium salts by bacteria.
Farmers in the US directly insert ammonia into field soil - for example corn fields. There is a limit to the amount they can apply before it degrades crop production.
This is due to: ammonia is a strong base and alters soils pH, raising it. High pH prevents nutrient uptake of iron for example. The corn is yellow with the veins a dark green color. You can find this information in any Plant Pathology introductory class. Excess nitrogen also "burns" plants - leaves turn yellow shrivel and die. The reason for this: the plant goes overboard storing all that wonderful nitrogenous goodness (from the plant's biochemical point of view), to the point where it becomes toxic.
Therefore, there is a limit to the either the amount of chicken manure (at 1.5% nitrogen see link) or the ammonia/ammonium content that is practical to add to soils. Pure manure is VERY poor soil. Bacteria love it.
https://en.wikipedia.org/wiki/Poultry_litter
So, I am indicating: raising nitrogen content somehow in chicken litter (without making it another kind of nitrogenous compound) results in problems at some point.
Note the study cited in the link about manure testing and crop yields. I believe the ammonia limit problem was a factor in chicken manure coming in as the #2 choice behind cow manure.
You can see ammonia wood staining effects on oak, for example. Oaken stalls used to keep chicken manure are much blacker than those used for cow manure. For those interested, ammonia stains oak for furniture (liquid ammonia, for example).
@phinds can tell you more about that.