E.g. a 25% average yield penalty in this meta-analysis:
Alvarez, R. (2022) ‘Comparing Productivity of Organic and Conventional Farming Systems: A Quantitative Review’, Archives of Agronomy and Soil Science, 68(14), pp. 1947–1958. doi: 10.1080/03650340.2021.1946040.
I studied the productivity benefits of adding beneficial fungi as part of my master's thesis. On average they provide a yield benefit, but it's not ubiquitous and they're far more likely to work in arid and semi-arid soils that have poor microbial diversity in their baseline. They don't tend to be as effective in temperate soils - partly because they have to compete with existing soil microbes.
This isn't categorically true if you're comparing the same variety of crop. Vaclav Smil does great work compiling data on this in his book "How to Feed the World". The overall environmental picture is also more complicated[1].
[1] https://ourworldindata.org/is-organic-agriculture-better-for...
Organic grown food tends to be higher in anti-oxidants and secondary metabolites, possibly because the plant immune system is activated more frequently due to better microbial biodiversity. From what I remember at least - it doesn't maintain any advantage in macronutrient density (carbs/nitrogen etc.)
There’s just not compelling evidence for your claim comparing the same varieties, the research exists.
It's hard to tell. There's no shortage of these types of questions, or people claiming to have the answers to them (like this guy). Reductionist Western science isn't amazing at understanding if these holistic thinkers are full of crap or not. Certainly some of his ilk are snake oil salesmen, and some are visionaries. I *tend to distrust the ones who are selling the solutions. I tend to trust farmers and farmer-researchers who are describing what they're seeing, but aren't selling anything.
A lot of people I know have used their Bio5 reactor and are pretty happy with it. It's hard to know what sort of effect applying compost extract has on agroecosystems, because these are complex systems and the tools we use to measure soils are fairly crude. But I know producers who have stopped using nitrogen fertilizers entirely, and are applying this extract instead.
If you're interested in soil health in general, and learning about what you can do on whatever land you might be managing (including a garden plot or a yard), an excellent starting resource is NRCS's soil health principles, https://www.nrcs.usda.gov/conservation-basics/soil/soil-heal.... If you are able to find ways to meet these principles in your context, that's like 80% of the battle. The rest will sort itself out. Or if you have more specific questions about other things these guys are schlepping, let me know and I can give you my two cents or point you towards more resources.
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Definitely give a shout if you have more questions. I'm biased but she's great at this. You can find some contact info for me in my bio.
e.g. https://www.youtube.com/watch?v=C3_w_Gp1mLM&pp=ygUUY2hpcnN0a...
It takes hardly any artificial fertiliser (10g per sq meter) to eliminate beneficial fungus from the soil, at which point you are basically running an open air hydro system and have to artificially add nutrients and adjust pH. It takes upwards of 3-5 years to start getting proper results from organic farming methods when switching back and basically involves adding years of organic material to kickstart the organic cycle.
It is totally possible to get comparable results to fertiliser based farming when farming organically, you just need to focus on 'growing' the soil, not just providing nutrient to the plants. In my opinion the former is farming, the latter is hydroponic production. Both have their benefits, it's just that one leaves behind barren soil and the other enriches the soil and is part of a natural cycle that leaves the soil exceptionally fertile.
The RHS (Royal Horticultural Society) sells little packets of mycorrhizal powder that you can put into your garden if you feel it is lacking beneficial fungi. Another more natural route is to bury a kilo of cooked white rice near a very healthy tree, where the soil is soft and 'healthy' then retrieve it after a week. It will be mouldy, but with the right type of mould. Mix that into compost, grow tomatoes in that compost, then when they are finished, chop up their roots, mix it into the compost again, add fresh compost from your compost bin to make seed compost. Mix that seed compost into whatever you want to 'infect'. Some people grow just the fungus using sprouted barley and add the mouldy sprouted barley to their compost.