This question has been already been partially answered on RG. See the links below.

The answer depends upon the researcher's field, experience, teaching load, admin load and the amount of support received. 

https://www.researchgate.net/post/For_selecting_a_PhD_student_by_professors_the_number_of_papers_are_important_or_the_quality_of_papers

https://www.researchgate.net/post/What_is_your_opinion_about_planning_the_number_of_published_paper_per_year

https://www.researchgate.net/post/How_researchers_are_evaluated_in_your_country_By_the_number_of_papers_over_a_period_of_time

https://www.researchgate.net/post/What_are_the_merits_and_demerits_of_writing_publishing_few_and_or_more_number_of_scientific_papers

https://www.researchgate.net/post/What_scientific_world_and_every_country_expect_every_year_from_scientists

I would like to clarify my question:

Is it known what is the average number of publications per one researcher per one year (based on statistics)? For example, in your institution, country or particular scientific field?

You can get an estimate for a researcher in your field or university by looking at the number of publications a particular researcher has achieved. Just type his or her name into the RG searchbox. Select someone similar to you. 

I link to a random example.

https://www.researchgate.net/profile/Morgan_Hawker/timeline

Dear Artis,

As for my establishment the university requires each academician to publish at least two articles per year on an average. However, most of us exceed this quota.

Cheers!

Academic writers who are not doing experimental research should have more articles

published than their colleagues who are doing experimental research.

Regardless of country, it is highly dependent on field and subfield. Some determining factors:

1. How many people are in the field/subfield (i.e. opportunities for collaboration and availability of peer-reviewers)

2. The state-of-the-art in the field - is it an emerging field where pretty much everything is new and publishable (e.g. advanced manufacturing technologies, artificial intelligence, autonomous vehicles, etc.) or it a field that is has a long history and therefore presents few major open problems (e.g. some areas of mathematics, structures, some areas of physics, areas of social sciences, etc.)?

3. The amount of funding needed to produce the research

4. The amount of time needed to perform experiments or run studies

5. The verification/validation criteria needed to show that a study is successful and useful (i.e. do we need to perform a longitudinal study over many years or can a simple case study suffice?)

6. The acceptance/promotion in the field of incremental work

7. The acceptance rate and review times of journals in the field

8. The view of conference papers, technical reports, and other non-reviewed publications (here, high-quality peer-reviewed conference papers are automatically assumed to be celebrated) in the field

http://blogs.nature.com/news/2014/05/global-scientific-output-doubles-every-nine-years.html The number of publications is growing. How fast is the number of authors of such publications growing? How to stay in the environment of those who claim to continue to be a "researcher"?

I would like to know how I can have access to the number of publications per researcher/year and by scientific area and by country or group of countries (e.g. Europe, USA). This information would be a great help.

depending on field of researcher, availability of instruments, skills of researcher in language writing, etc

Mario Cunha , have you tried this one:

https://www.scimagojr.com/countryrank.php

But I have not seen date about number of publications per researcher / year. I guess that one of the approaches would be to find number of publications per country and then find number of researchers in that particular country. But if you find this data for all countries, please share this information with us.

Publish or perish...