Just my opinion but after twenty years what has it turned into? 20 year old horse manure.
I think once it has been wet and worked into the soil it will be a great soil amendment. It
might be good to break it up some first before wetting, but I think the worms will actually take care of that process once it is in the soil.
There is some argument that humus does not even exist, but that really depends on the definition or useage of the term. It seems to be a term with no exact definition that everyone can agree on.
https://www.gardenmyths.com/hu...
This really makes it hard for me to understand all the new products and fertilizers just recently on the market(at least new to me) with humic products added with a large increase in price for it. I have read it is often nothing more than coal added.
Maybe it could be labeled dehydrated aged composted horse manure with humus, you could then bag it an make a small fortune.