Did you just make up that statistic? or do you have a credible link that backs that claim up?
It is a pretty well known datum. Many would say the drop in human population would be much more.
Here is a link and explanation from 2015. The number is undoubtedly higher now.
The red line represents the size of the global population which would therefore be supported without the use of nitrogenous fertilizers. This is shown simply as the actual population minus the number of people reliant on them for food production. Without this innovation, global population may have been reduced to only 3.5 to 4 billion people.
