Then you might have to look for other revenue opportunities.
I don't think anyone advertises on Adsense related to Books. Do you know any other websites on the same niche running Adsense ads?
You can directly contact the publishers and book writers and write a review for their books. But this only works if you have a good audience and time and energy to manually find and reach to authors.
Honestly, I think you should not expect to earn good amount from ads and affiliate. Direct contact and review would suit better. Hope it helps.