Steven Edholm of blog Turkeysong – Experiments and stuff, has put together a great list of citations compiled from a search of 19th century literature in googlebooks using the search term charcoal fertilizer.

This is a short version on his website >>>> or he has put together a long 179 page PDF available here >>>>

My personal and professional option is that carbonised biomass produced or developed for agricultural/horticultural application should be classed as Biochar. In the case of many of these books the term Biochar had not yet been coined.