.

Yes, I've been wondering that...

OED gives prolificity (1718) - The quality of being prolific; fruitfulness; fecundity.

with slightly earlier

prolificness (1678) - The quality of being prolific (in various senses); esp. great or abundant fruitfulness or productiveness, productivity.

and prolificalness coming in slightly later (1699) but made from "prolifical" as a 1608 adjective, +ness. Given as "now rare" but an example from 1996.

Edited by EmmaD at 14:22:00 on 04 September 2013

I quite like the idea of "prolifical", it seems so versatile...

In a pub filled with badly written yokel stereotypes:
"That there writer, he be quite prolifical, so he be."

In the atrium of a badly written ivory tower:
"And of course, I can highly recommend Xavier Preveldicott. Some have mistaken his prolificality for the garrulousness of a talentless hack, yet his quality is as steady as his prolifical output."

In a book club:
"Of course, I haven't read all his works, one couldn't with a writer so prolifical, yet his latest book rather makes one want to try."

Edited by GaiusCoffey at 15:18:00 on 04 September 2013

Gaius.

I'm trying to think of rhymes for prolifical, but can only come up with Pontifical, which is a cynical joke waiting to happen...

A writer with output prolifical,
Tried ever so hard not to ridicule
Reviewers whose nose
Out-of-jointed at prose,
Like his, that was oft times political.