No rule in Nigeria specify the minimum or maximum number of article to be published in a single year. We only have required number (minimum) of article to be published before the next promotion.
There are no limit as such but no unethical means should be used to publish more numbers of papers. Number of publication does not matter, only quality and novelty of the published work matters the most. Regards
I think first thing to be considered is the quality of the paper. If it's an impact journal that indexed in database such as scopus, web of Science I will say one paper is okay per year. But if its Nigeria University based paper, then unlimited.