Comment by spenrose

A number of commenters are pointing out that natural fertilizers exist. That is true. It is also true that artificial fertilizers were invented because around 1900 humanity ran out of biologically accessible ("fixed") nitrogen that it could convert to crops. The key nitrogen atom in roughly half of the amino acids in your body was part of a nitrogen-nitrogen pair floating in the atmosphere until it was fixed in a factory. If all the factories making fertilizers shut down tomorrow, there would be mass famine.