Interesting premise. I wonder if civilization would collapse, or if we'd be able to adapt our agriculture to more legumes and other vegetables quickly enough to avoid mass starvation.
The US plants more soy than wheat already so the adapting part would probably go OK. The bigger question would be the math about calories (it probably works out, meat production consumes a lot of calories).
I guess we could also plant lots of potatoes (which produce more calories/acre than soy).
And the more meat a county eats, the more is can divert stored feed for that purpose, modulo grain sorghum, which isn't normally a human food, to directly feed humans.
Feed Conversion Ratio (FCR) for cattle is about 10, pig 3, sheep 5, and chicken 2. That means we could feed about 10 times more people per hectacre on grains than using that grain as feed for beef. Ruminants are important for nutrient cycling and other ecosystem services, but far from efficient as a food source for humans. They are best utilized on marginal land where agriculture isn't ideal.
Yeah, in the US at least, the normal pattern is to raise cows on pastures, sometimes out in the dry west fantastic acreage of it, 1,000 acre ranches can be considered tiny, 10s of thousands are not uncommon, and/or including grazing rights.
Then they're sent to a feed lot for some period of time to fatten up.
Ah, from the article you linked: "However, comparisons of FCR among different species may be of little significance unless the feeds involved are of similar quality and suitability."
So cattle might be more efficient than appears at first glance, since as ruminants they're initially fed stuff you can't feed other animals (ADDED: including humans), especially "on marginal land where agriculture isn't ideal", or perhaps as part of a crop rotation cycle. Alfalfa is a 3-for, a rotation cycle that's not e.g. corn or soybeans, a nitrogen fixer, and tasty food for cows.
And all the above isn't the best for our topic at hand, for that alfalfa and such isn't stuff we can digest, nor is silage from corn leftovers, so it mostly feedlot cow food we could redirect to humans.
I agree with you that it's mostly feedlot grains that we could redirect to humans, and that feedlot grains is a surprising amount of what we produce in total.
"More than half the U.S. grain and nearly 40 percent of world grain is being fed to livestock rather than being consumed directly by humans"
Topsoil erosion is already a massive problem.[1] So far we've been able to mask the damage by substituting fossil fuel inputs for soil fertility, but realistically soil husbandry is the only sustainable way to grow food.
Heck, many people nowadays aren't even aware that soil organisms can manufacture bio-available nutrients from local minerals and the air.[2] The dominant view of soil seems to be as an inert tank that needs to be "refilled" with imported fertility.
In that context, for a couple or so of years you don't worry about soil erosion, except to avoid a repeat of the Dust Bowl, you worry about people not starving. Before AKA "now", and after the emergency period, yes, you worry about it, as we do now.
Don't be absurd. There are dozens of wheat pathogens alone (here's my favorite: https://en.wikipedia.org/wiki/Stem_rust ) and we as a civilization have been dealing with them for a long long time.
Indeed, read a infectious disease news collection source like http://promedmail.org/ long enough and you might be surprised we have anything to eat beyond Soylent Green. Everything you love to eat has a host of pathogens that want to eat it first.
Try gardening/farming. Starting with eggs. Snakes, weasels, raccoons, even the hens want them. Hawks want my chicks, as do snakes, raccoons, weasels, foxes, bobcats, and coyotes. Weasels, coyotes, foxes want the pullets and adult hens. Its like anything I want to raise is a buffet for nature. On the other hand, I have an electric fence.
So many people have stopped their small scale chicken raising/egg production, like one family I know, after they learned "fox in the hen-house" isn't just a turn of phrase.
Both my parents grew up on farms, and we kept a big garden when I was growing up, so I know this very well, although reading the article that link collects for many months was serious sobering.