There has always been alternatives to commercially produced fertilisers. Horse and cattle manure, are the obvious ones, as well as chicken pigs etc. It is also a fact that it is not a necessity to add fertiliser to any plant.The only requirement is sun and water to photosynthesise and produce nutrients.
One of my first books, probably in the 60s, told how people used to make bonsai fertilizer by soaking manure in water for long times, squeezing it out, and other steps. There was a similar process involving dead fish.
It did not recommend doing it then, in the 20th century. We are now in the 21st. Don't. Or, if you do wear gloves.