Unless you’re in full apocalypse mode, every man for themselves, I’d expect for the most case people will learn from their neighbors quickly enough — as long as a survivable subset of the population knows what they’re doing
What’s going to kill billions is the lack of industrialized farming productivity, but you don’t expect every individual to know how to resolve that
I doubt even the lack of industrialized farming productivity will "kill billions".
It will certainly switch diets and most probably cause hunger and malnutrition for some time. But we can support billions of people, given the right diets. We cannot support billions of people's mcnuggets, beef burgers or cornflakes with milk. About a third of my food comes from stuff I make, grow and harvest myself. I can up that, if I need, but preparing, growing and harvesting are a hobby, not a full-time endeavor. I'm certain I can't up it to 100%. Maybe not even 50%. But some neighbor, friends and family can help out (and I them) and I'm certain with some ~100 people we could be self-sufficient. Sober, sure. But not dead.
(I would die from lack of insulin within months, though. TII. So I am aware of how dependent on industry and high tech I am)
No, without industrial scale fertilizer production, there is no way to grow enough food for our current population. Natural processes simply can't fix nitrogen fast enough. The main reason populations started exploding in the 19-20th century was because we found a way to produce nitrogen fertilizer in absurd quantities very cheaply.
If that link in our global industrial chain breaks, a lot of people will die. We can, of course, still grow food, but not anywhere near as much and it will take a lot more care and attention to not deplete all available soil in a generation or two.
In a hypothetical apocalyptic scenario, we might lose a lot of institutional knowledge about agriculture. It's not hard to imagine some average joes trying to farm the wrong way and accidentally starting another Dust Bowl. After all, that's how it happened the first time.
Feeding 8 billion people is so, so much more complicated than just putting some plants in the ground. That we can do it at all is an absolute miracle of technology. We simply could not do it with only naturally available resources. Not by a long shot.
According to most sources I can get to with my amateur knowledge, a giant portion of proteins is "wasted" by "producing meat". Another large portion is wasted because of poor logistics and wasteful behavior.
If everyone stops eating meat, and starts eating the proteins themselves, we win some 1000% to 25000% (sources range from 10 to 25x the proteins in/output when producing meat). Meat is just a terribly inefficient way to produce proteins. (Edit: to be clear, "meat" differs a lot: chicken apparently being rather efficient, more even than cheese, beef being amongst the worst).
And if then the resulting food sources are grown efficient, and all, or a lot of waste can be eliminated by shortening supply chains, sourcing JIT (no avocado's in winter in Europe, no tomatoes in snow), I'm pretty sure we'll get a long way.
But, sure. If some rich countries keep demanding giant portions of global protein in e.g. soybeans and corn to feed cattle to make burgers for 7 meals a week, then certainly: people in countries who cannot afford to compete with the soy-prices will starve.
Market is about supply and demand. People demand meat. Regardless of how inefficiënt it is produced.
And, no surprise, this isn't a free market at all. At least in Europe, meat, dairy (and on lesser extent crops) are heavily subsidised.
https://ourworldindata.org/grapher/feed-required-to-produce-... has a quick overview. My numbers aren't wrong, but, as always, they do need context (i.e. not all input is currently human consumable. Oos, many input is grass, which is rather ineffective land-use, i.e. the same km² could produce a multitude of human edible foods)
> About a third of my food comes from stuff I make, grow and harvest myself.
1/3rd of value or flavour is relatively easy. 1/3rd of protein or calories is a lot harder.
Need those mechanized 2000ac farms growing corn, canola or wheat to supplement the homegrown tomatoes/potatoes/peppers/herbs/apples. But it’s impressive what can be done with a somewhat small backyard in terms of value/flavour and not a lot of effort.
My diet is vegetarian, so a lot of flavor is that staple.
My tiny lot brought me all the potatoes, corn, beans and pumpkin I need and some more. Our five walnut trees, shared with 12+ households, produce some more protein.
I obviously still buy rice and a lot of wheat and rye meal to bake my bread and pizza and to make pasta.
My point was that I don't need the large industrialized food industry to feed myself. My point was not that I can do without a society with specialized and efficient food production.
What’s going to kill billions is the lack of industrialized farming productivity, but you don’t expect every individual to know how to resolve that