several years ago in my country located in southeast asia experienced a fertilizer crisis. However, because of the cleverness of the farmers here, they have even made new discoveries, such as organic fertilizer from household waste and the natural environment, even banana trees, which generally only take the fruit after being cut down. so now in my country banana trees are fermented into fertilizer and animal feed. and it turned out to be effective.
If we consider that people in the past were also engaged in agriculture and did not have artificially created fertilizers, then it is easy to conclude that they used something they could find in nature. For my garden, I use exclusively fertilizer that I make from two plants that are nothing particularly rare or exotic, and that is nettle and comfrey.
Fertilizer can be made in two ways, by fermentation (1kg plant + 10 liters of water) which is then used diluted with water to water the vegetables under the roots, or by soaking these plants in water for 24 hours using this water to fertilize plants through leaves. This is very effective because the plant gets all the necessary ingredients for growth, and nettles and comfrey can be found and harvested completely free of charge because they grow like wild plants.
As in the case you described, people have to deal with the situation they are in and help themselves by producing what they cannot buy on the market. Every country should place special emphasis on self-sufficiency, because being dependent on someone or something can ultimately mean a matter of life and death.
If people will only have the eagerness to explore new things just to fill in the gaps or lack of supply in a country things will be quite easy to solve. We only have to be efficient and creative so we could contribute something during times of crisis. We could make alternatives to survive. If there's a lack of supply of wheat then we could switch to rice or corn. This wheat crisis couldn't get worse if people will only be wise.