How did the agriculture survive before fertilizers?

Answer 1

All fertilizers did and continue to do is accelerate the growing process by constantly adding energy in the form of nutrients. Agriculture survived just fine without fertilizers-- the natural biochemical cycles ensured that key nutrients and proficient components in the growing process were used by crops. These crops (however meager) would feed the population of humans to some degree. It is also worth mentioning that agriculture has completely been modified since the practice of fertilizing the soil, sometimes for the worst.

The difference between then and now is the simple fact that there are more people today. There was a time before the industrial production of fertilizers that humans were growing too quickly and there wasn't enough food to feed all. But fertilizers create environments of crop-friendly soil even when it wasn't before-- effectually bumping up the human population's carrying capacity.