Comment by accidentallfact

There is no reason to believe that a lack of nitrogen was a problem in particular. It seems that most effort was spent on getting fertilizers with phosphorus and other minerals, nitrogen was secondary, as many plants can obtain it from the air. If anything, it allows our modern, heavily cereal skewed diet. Poor nutrition rarely meant an absolute lack of food, most of the time it only meant insufficuent quality, and the green revolution was a massive step backward in that regard