having a field full of different crops is not useful.

Really, or is that just an unquestioned "industrialized farming is the progress because volume produced (for a short time, wholly unsustainably, with loads of hidden overheads) is big!" perspective? You see, biological systems are far more complex than a few years of crop output, and such a simplistic take is clearly missing the bigger picture.

A field full of different crops is much more useful than a field of one crop because (A) it requires less maintenance (B) it can feed you more fully from a dietary perspective (C) it encourages a proper ecosystem to develop (insects, birds, etc.) (D) it is far more likely to prove a sustainable user of soil nutrients (E) with a higher density of vegetation and multiple layers of canopy, it will retain and therefore use less water, better surviving fluctuations in precipitation.

It would lower yields,

I believe evidence is to the contrary, but do not have the time to research just to convince you. If you are interested, please start by reading the Japanese farmer/microbiologist's book The One Straw Revolution I posted earlier in this discussion.

...be difficult to harvest...

If you haven't had to do much maintenance on the crops at all (weeding, watering, pesticides since a healthier ecosystem will prevent plagues of most pests, fertilizing, etc.) then a little more harvesting time is no issue.

(mechanical harvesters rely on uniformity)

We could always harvest ourselves on smaller scale farms, and anyway we'll surely make better machines. It's hard, but not that hard.

...and consumers like uniform crops.

Debatable. Organic Farmer's market, anyone?

It also doesn't make sense to take genetic diversity in a crop and plant it in a field because it's completely ignoring our ability to design local crops — ones that are more drought tolerant given a region's rainfall, or ones that could handle colder temperatures.

Nature does this automatically.

If your field of genetically different crops are all planted together, half may die if there's a cold spell.

Sure. But if you then have a virus that infects cold-spell-resistant-genotype in the same year, at least you have 50% of your crops instead of none. And your overall time input was close to zero. And your seeds are real, fertile ones, that you get every year for free, giving you true food security.

Uniform genetics allow us to really understand what a single field is going to do, and this is why it's so common. It's also why there are vast field trials —sometimes decades long— for all crop varieties.

We only have some idea. We can't predict much of the future, such as emergent pathogens or significant climactic variation.

Take the wheat example I gave above. Even if you were to plant every variety of hexaploid wheat in a field, despite different flowering times, milling characteristics, best environments, etc. one rust would still kill them all.

If you have diverse crops planted, the likelihood that one rust will spread to all physically separated groups of wheat is far lower. In addition, even if they all die, you still have food, and there will often be seeds that have survived and will return in the next year... Oh wait! That only holds true for real seeds, not the GM sterilized-for-the-profit-of-the-few industrial ones.

There is no resistance allele in this entire species of wheat. This is why researchers had to go find Sr35 in an ancient relative.

Aha! So here we have an example of a plant that we heavily domesticated, destroying genetic diversity and creating gross vulnerability to a single pathogen. That illustrates my diversity point well.

You could make the claim, well, we should be growing that ancient relative, but this is silly too — it would be risky given it hasn't undergone the same selection for agricultural hardiness as modern varieties.

See, here's the thing. We don't know the future: so who are we to select? Nature does all this by itself. It's a bit silly to waste our time trying to out-nature nature, when we could adopt a different philosophy and significantly increase our food security in measurable ways: maintaining long term genetic diversity, and ensuring resistance of annual output to single pathogens or other unexpected environmental factors.

As I said, there's nothing magical about having a field of diverse crops.

But there is. By being closer to nature, it survives and thrives on its own with minimal effort.

A field's population will always be smaller,

False.

... and encapsulate less diversity than that all of the world (and in other relatives).

Sure, but that's a pointless observation. In any event, it will encapsulate a subset of diversity for each plant that evolves to suit to local conditions, and that is more resistant to crop failures than a single genotype.

If your so called black death came along and killed all but a few plants, why would this help?

Because you have multiple crops, so the reduction in one is less significant, and because your local genotype is better suited to other aspects of the environment and most challenges to plants aren't Tom Clancy killer viruses.

There's still too little to feed or sell.

Really, you should read about alley cropping, then read The One Straw Revolution, then watch some videos of permaculture gardens. You'd be surprised just how wrong you are about output from industrial agricultural monocultures versus diverse crop interplanting.

This disease already decimated the population, and our best approach is to breed an entirely resistant population the next year — not throw in more diversity and hope for the best.

I would say our best hope is not to do anything, and to allow the more resistant or miraculously preserved subset to return in its own time, lending its former space to other species as nature sees fit.

We can intelligently leverage diversity in breeding, which is more optimal than just planting diverse fields.

More optimal .. for what set of conditions? Not a sustainable or self-sufficient food security goal for most of the human world. Though, perhaps more optimal for profits for industrial farming companies who have little interest in actually looking after the land, water tables, ecosystem or community past the bare minimum necessary to ensure continued profits.

> Third, your backcrossing line is dubious. Biology is good at survival, we don't need to tend to it ourselves. If we reach a state where we do, then gee golly: we've clearly buggered up hundreds of millions of years of success in a right jiffy!

Sure, but then go eat teosinte rather than maize. I think you're forgetting that we domesticated varieties to survive with our help, and to feed us. Through breeding we can grow maize in Wisconsin rather than Mexico. If backcrossing is dubious to you, you should stop eating all crops because I guarantee all have had parents that have been extensively backcrossed.

Historically speaking, large scale agriculture was heavily linked to the emergence of a state, wielding a monopoly of force to extract corvee labour, military service and taxation from a population. Perhaps it's time to put that history to rest and consider less uniform crops, more seasonal diets, and a swing back toward more decentralized production of a greater variety of foods.

Please if you have some magic way to do this and feed met the world's food demands, become a plant scientist! But I think you will find that it's just not this easy.

Actually I'm going right for the throat: the financial system. Once that's done I'll be happy to retire to farming!