After a rain, as the soil goes from waterlogged to dry, there are phases that are hostile to root hairs and ones that are conducive. So the plant roots pulse with these cycles, advancing and retreating, sometimes arriving at places vacated by other plants. By this mechanism, any plant can scavenge some of the nitrogen left in the decaying root hairs of their neighbors.
I would also warn that thinking nitrogen=legume is a potentially limiting strategic error. While something like 7% of all plants fall into the Fabaceae (legume) family, some other pockets of the Fabales order also have root nodules, in particular, alder, and up into the Rosids clade (buckthorn, ceanothus), and then a few odd stragglers like borage, which makes me wonder if it's a taxonomic problem, parallel evolution, or what.
And then there's mondo grass (asparagaceae), which nobody expects to have root nodules. I knew about that plant for about two decades before someone pointed out it's nitrogen fixing, and that's not even in the wikipedia article. And in fact I'm having a dickens of a time finding a citation for that.
https://www.ers.usda.gov/publications/pub-details/?pubid=440...
Industrialized farming practices are capable of changing.
There have even been a few studies that warn that some strains of conventional crops are losing the ability to make this exchange. When we hit peak phosphorous and start taxing anhydrous ammonia production, these strains are at risk of going extinct (hopefully not enough of any crop to take us with them).
The wrong question is, "how many calories of <X> can I get out of this field in a year?" The right question is "how many calories can I get total out of this field in a year" and there are a number of people out there demonstrating that they can get about 50% of the conventional yield from an acre, but for 4 different crops, and a few other things thrown in to get over 2x the total yield.
The "problem", in scare quotes, is that these solutions take more thinking and knowing than scourging your fields every year. But since running a farm practically takes a bachelor's degree these days, that's not really a problem of lack of resource in that area. It's more a problem of perspective and focus.
I agree on this point. Every successful farmer I've met has been of notably above average intelligence. However at the family farm scale it's a very fragile business. A small increase in input costs can greatly reduce or eliminate profitability. While I think permaculture, no-till, and other such techniques are great, we have to acknowledge that they require considerably more labor than running a combine harvester over corn or soy fields. The labor shortage is bad enough that even generally immigration skeptical rural areas welcome H-2A migrant workers. And while the best American farm workers are every bit as hard-working as the best Mexican seasonal workers, the average Mexican that comes to the USA in the program is considerably more reliable than the average American these days.
(The most obvious could be that nobody want to buy some of the other crops, so while you could get the calories out, you can't get the dollars out, and the calories would go to waste if everyone did that.)
A lot of US agriculture is done on by contract operators. Bill Gates seems to work mostly in that model.
I mention Gates because what he says suggests that he'd love to see that claim pan out on a large scale. Also, he's known for insisting on high dollar yields.
And yet, we're talking about demonstrations and not actual significant experience.
Maybe Gates is lying about his social goals AND also isn't profit-maximizing.
But, if he isn't, why aren't the demonstrators doing good and doing well (2X production is a big bucks) by doing this stuff at scale somewhere in Gates-land?
https://www.ers.usda.gov/publications/pub-details/?pubid=440...