Bagmuck
I'm going to put this here, for now and maybe develop it further.
As a student I worked on a market garden which also had a small line in agricultural supplies. Every so often we had the job of loading bags of inorganic fertiliser onto lorries or trailers. The word used for it was bagmuck.
I think bagmuck captures rather well what this is. It's a substitute for muck, dung, manure, that comes in a bag. From ICI in those days.
Bagmuck /contd.