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It's been a while since I found myself disagreeing so strongly with a piece on agriculture.
It would be stupid *not* to rely on the insight and accumulated experience of local farmers, or local genetic resources. The opinion piece could have made that argument. Instead, they decided to present it as a competition between traditional knowledge and "external tech."
Traditional approaches get you traditional results.
Here, by contrast, is what happens to maize yields if you use modern technology. Make no mistake - most of this increase is due to *better genetics*, although fertilizers and pesticides obviously helped. We could show similar pictures for many different crops and countries. 
That's a six-fold yield increase. (Source for the chart: agry.purdue.edu/ext/corn/news/…).
The authors claim that "small-scale family farming, ..., despite the popular misconception that industrial systems are necessary to feed growing populations, continues to produce most of our food with fewer resources and less harmful impacts than the industrial model." Um, no.
Most of the world's farms are small farms (less than two hectares), but most of the land is in large farms. sciencedirect.com/science/articl…
Small farms (<2ha) probably produce something like one-third of the world's food supply. Not bad, but not exactly "most of our food", as the authors claim. sciencedirect.com/science/articl…
But how can this be? The authors even link to another article explaining "family farms produce over three-quarters of the world’s food. The FAO also estimates that almost three-quarters of all farms worldwide are smaller than one hectare"!
Well, you've been tricked by a stereotype. You read "family farm" and you think "small farm" - but most *large* farms are family farms, too! Even in the US, presumably as close to "industrial ag" as we can get, most of the farm production happens in (often large) family farms.
But are the small-scale, traditional approaches more sustainable? Yes, perhaps, if you compare environmental impacts *per unit of land*. But the point of farming is to produce food. Environmental impacts *per unit of food* typically look very different.
For example, here are greenhouse gas emissions from beef expressed *per kg of protein*. By far the highest emissions intensity is found in ... traditional systems, where productivity is low.
The authors write that "agriculture currently produces roughly 11% of global greenhouse gas emissions, rising to as high as 29% taking into account the entire food system". Surely this means all the industrial processes? Production of fertilizers, transport, processing? Nope.
The vast majority of greenhouse gases are directly linked to agricultural production, or land use changes (deforestation etc.), roughly 50/50. This accounts for some 80-86% of the total "food system" emissions. annualreviews.org/doi/abs/10.114…
And all of this is just in the introduction of their piece.
The rest of the piece takes for granted that synthetic inputs are bad, but worries that moving to organic bio-inputs is bad too. "The problems with introducing “bio-inputs” ... are displacement of local practices and the risk of creating new forms of dependence."
Now, perhaps this is reasonable for the farmers in Guatemala they studied - I don't know the situation. But that's not the scope of the claims made in this piece. We're not talking about "sustainable agriculture in Guatemala"; we're talking about sustainable agriculture, period.
So, let's take a look at what this "no external input" strategy means for other regions.
This chart (via @OurWorldInData) shows nitrogen balances, an essential plant nutrient. Orange or red means deficiencies, which in turn gives you low yields... as in nearly all of Sub-Saharan Africa.
If you don't like "external tech", then good news - Sub-Saharan Africa has mostly avoided the dependence on external inputs... Low use of synthetic fertilizers, of modern varieties, or irrigation. And spectacularly disappointing yields.
Now, agriculture in SSA is facing numerous challenges; it's not as simple as throwing some nitrogen on the land and waiting for the bumper crops. I don't doubt that there is a wealth of local knowledge and genetics which can help improve on the current situation.
But let's not kid ourselves for a moment that traditional ways would somehow be sufficient.
The challenges facing global food and agriculture are enormous. By 2050, we'll have some 9.7 billion people to feed. Doing so without destroying the planet is going to be tricky, even with technological progress.
The authors conclude: "If sustainability is the true objective, we need to focus, not on new technological fixes, but on the recovery of local, time-tested agroecological practices" - strongly disagree. What we need is pragmatism.
Can traditional insights help? Sure. Are they the answer? No. There are no silver bullets. We'll need all the tools we can get.
