I don't think you really answered my question.... at least to my satisfaction.   You said that your farm fields have "manure pressure".   Then you said that fields get chicken litter or hog manure "every once in a while".  To me, manure "every once in a while" is not "manure pressure.  So, can you elaborate what you mean when you say your fields have "manure pressure"?  What is "manure pressure"?

Here, we use manure most every year, not "every once in a while".  Manure applied every once in a while is next to nothing.  

My understanding is that rock phosphate is slow to break down and release.  I could be wrong, but I would think that phosphorus from rock phosphate could show up in a soil test, but not be readily available to the plants.  I would think the nutrients in manure are more readily plant available than what is in rock phosphate. That is my way of thinking.