Let microbes
stand in for chemical fertilizer.

Through Chapter 4, the conclusion came out like this.

• Chemical fertilizers will rise structurally in price
• Industrial agriculture that depends on chemical fertilizer cannot stand
• Full self-sufficiency cannot stand either
• The shortfall is covered by imports, and domestic production migrates to methods that do not depend on chemical fertilizer

That last item — "methods that do not depend on chemical fertilizer" — this chapter says, concretely, what that is.

The conclusion is agriculture that uses the work of soil microbes. This is the scientific core of the family of methods that have been called "natural farming," "regenerative agriculture," and so on.

5.1 The soil already holds enormous phosphorus — "legacy phosphorus" and biological mining

Let me start with one surprising fact.

Most farmland already holds enormous accumulated phosphorus.

It may sound surprising. In an "era when phosphate fertilizer is running short," is there really phosphorus in the soil? There is. Often there is, in fact, an excess.

On farmland that has used chemical fertilizer, the plant uptake rate of applied phosphorus runs from a few percent to about 20%, with the remainder fixed in the soil.

What does "fixed" mean here? Phosphate ions bind with iron, aluminum, and calcium in the soil to form insoluble phosphates. Plants cannot absorb insoluble phosphorus. So most of the applied fertilizer remains in the soil in a form plants cannot use. This is called "legacy phosphorus."

After decades to a century of chemical fertilizer use, the topsoil of Japan's farmland is estimated to already contain enough phosphorus to grow crops for years to more than a decade.

Add to that: in regions with geological mineral sources, nutrients beyond phosphorus are also potentially abundant.

• Weathering of green chlorite schist — silicate minerals containing magnesium and iron dissolve over long timescales
• Alluvial silt from flooding — mineral-rich sediments brought from upstream
• Volcanic ash soils — rich in many trace elements beyond phosphorus

The problem is not a shortage of phosphorus or nutrients. It is the inability to convert the enormous nutrients already present into a form plants can use.

The architecture that changes this is "biological mining" — the autonomous nutrient-recovery system based on the symbiosis of mycorrhizal fungi and plants, touched on at the end of Chapter 3.

Rothamsted long-term experiments — 8 years of normal growth on legacy phosphorus alone

The amount of legacy phosphorus is vast, and it is estimated that even if external phosphate fertilizer input is halted entirely, enough already lies in the topsoil for crops to grow healthily for several years, more than a decade, or even decades.

In long-term field experiments conducted in England (Rothamsted),

in barley cultivation, even when phosphate fertilizer was halved and finally halted entirely, for the first 8 years the surplus nutrients in the soil (legacy phosphorus) were sufficient to grow the crop normally, with no impact on yield.

In other words, the real challenge of modern agriculture is not an "absolute shortage of phosphorus." It is the lack of a biochemical mechanism to unlock the vault of accumulated "legacy phosphorus" and convert it into the soluble forms plants can use.

Japan's Andisols — exceptionally high phosphate-fixation capacity, even by world standards

This phosphorus accumulation is especially pronounced in Japanese soils. The volcanic ash soils (Andisols, Japan's kuroboku volcanic ash soils) that dominate Japan's farmland have a high capacity for storing organic carbon, but also have very distinctive chemical properties.

• Andisols contain large amounts of amorphous aluminum (Alo) and iron (Feo)
• The phosphate absorption coefficient (the soil's ability to bind phosphorus tightly to soil particles, turning it into insoluble forms unavailable to plants) is proportional to the Alo + 1/2 Feo content
• As a result, Japanese soils have exceptionally high phosphate-fixation capacity, even by world standards

Farmers, to prevent phosphate deficiency in their crops, have for decades applied excess phosphate fertilizer continuously. Examples of organic phosphorus accumulation in Japanese farmland soils, based on measured data (about 50–60% of total phosphate accumulates as organic P):

This phosphorus is physically and chemically there, but it lies dormant as "unavailable phosphate," which plant roots alone cannot absorb. There is no physical necessity to keep importing expensive phosphate rock from outside. How to mobilize this "phosphorus already present" is the core determinant of the economics of next-generation agriculture.

How the autonomous loop is configured

Instead of continually supplying precisely calculated chemical fertilizer from outside,

• Atmospheric CO2 → plant photosynthesis → soil via root exudates
• Root exudates feed mycorrhizal fungi
• The fungal hyphae dissolve legacy phosphorus and weathered minerals in the soil
• Returned to plants as nutrients

an autonomous loop is set up. The cost structure is fundamentally different.

This is where soil microbes — especially mycorrhizal fungi — enter.

5.2 Mycorrhizal fungi — the plant's hidden partner

Plants look as if they are absorbing nutrients directly through their roots. The reality is different.

About 80% of land plants form symbioses with mycorrhizal fungi [unverified].

Mycorrhizal fungi are fungi (relatives of molds) that live inside or around plant roots. They extend hyphae into the plant's roots, penetrating into the cells of the root. From there they extend countless hyphae outward, building a vast network in the soil.

The breadth of this network reaches hundreds to thousands of times that of the roots themselves [unverified]. Plants can collect water and nutrients via mycorrhizal fungi from regions their own roots cannot reach.

A universal symbiosis built over 475 million years of evolution

The history of mycorrhizal–plant symbiosis is ancient, going back about 475 million years, to the early stage when plants emerged from the sea onto barren land. The first land plants, in a harsh environment of rock and sand where the very concept of "soil" did not yet exist, only succeeded in colonizing land by partnering with fungi to acquire essential minerals. This co-evolution of plants and fungi fundamentally rewrote the planetary carbon cycle, bringing about a dramatic environmental change in which atmospheric carbon dioxide (CO2) was reduced by as much as 90%.

Even today, this partnership is maintained with extreme robustness. By the latest estimates, 80–90% of plants form symbioses with mycorrhizal fungi — an overwhelming majority of known land-plant species. There are several diverse groups, including ectomycorrhizae common to trees, and arbuscular mycorrhizal fungi (AMF), which form symbioses with nearly all major crops — maize, wheat, soybean, and others.

In nature, plants absorbing nutrients alone is the exception, not the rule. "Outsourcing to mycorrhizal fungi" is the default strategy of plant survival.

The spatial reach of the hyphal network — hundreds to thousands of times

The volume of soil a plant can explore with its own root hairs alone amounts to just a few percent of the total soil. Most of the fine gaps inside the soil (micropores) are too tight for even root hairs, let alone roots, to enter. This is where mycorrhizal fungi exert their overwhelming physical advantage.

Arbuscular mycorrhizal fungi (AMF) penetrate even into the cortical cells inside the plant root, forming a tiny nutrient-exchange organ called an "arbuscule" (the tree-shaped body). From there they radiate countless microscopically thin hyphae outward into the soil, building a vast three-dimensional network (mycelium).

The physical scale of this hyphal network is hard to imagine:

• Reaching a wide area, 45–60 cm or more beyond the root itself
• Expanding the plant's effective nutrient-absorbing surface area by hundreds to thousands of times
• Up to about 90 m of fungal hyphae per 1 g of healthy soil
• It is not unusual for several kilometers of hyphae to be threaded through a single teaspoon of soil
• The total length of fungal hyphae in the top 10 cm of soil across the entire planet is estimated at about 4.5 quintillion km — half the Milky Way galaxy

Because hyphae are far thinner than root hairs, they readily enter microscopic soil pores and access water and nutrients tightly bound to mineral surfaces. Plants use this "world's largest straw" and "giant underground communications network" of mycorrhizal hyphae to gather resources from a wide range — including regions their own roots could never reach.

What mycorrhizal fungi do — a sophisticated nutrient-supply mechanism

The Australian soil scientist Christine Jones summarized it as follows in her paper "Light Farming" (2018).

• Up to 90% of the nitrogen and phosphorus the plant needs can be supplied via mycorrhizal fungi
• By secreting powerful enzymes such as phosphatase, and organic acids, from the tip of the hyphae, they dissolve hard-to-solubilize phosphates bound to iron and calcium in the soil and convert them into phosphate ions plants can use
• Phosphorus uptake by hyphae is 6 times faster than by root hairs; transport is 10 times faster
• Mycorrhizal fungi can directly absorb organic nitrogen such as amino acids in the soil and, while preserving the molecular structure, deliver it through the hyphal network into the vacuoles of root cells, then transport it systemically all the way to the chloroplasts in the leaves
• They sharply increase the plant's drought tolerance (the network gathers water)
• They form physical and chemical barriers against pathogens, induce the production of defensive enzymes, and suppress and isolate uptake of heavy metals and excess salt

So you can almost say "the plant employs mycorrhizal fungi as a contractor." The plant is good at producing carbon by photosynthesis. Mycorrhizal fungi are good at gathering nutrients in the soil. They divide the labor and trade.

Plant → mycorrhizal fungi: carbon (up to 20% of photosynthetic output) Mycorrhizal fungi → plant: water, phosphorus, nitrogen, minerals

This is a symbiosis built over 475 million years of evolution.

The synergistic consortium: AMF + phosphate-solubilizing bacteria (PSB)

AMF do not work alone — they form a synergistic functional consortium with PSB (phosphate-solubilizing bacteria).

• PSB produce inorganic acids such as carbonic acid (H₂CO₃), hydrochloric acid (HCl), nitric acid (HNO₃), and sulfuric acid (H₂SO₄), and a variety of organic acids, with the capacity to dissolve and solubilize insoluble inorganic phosphorus
• AMF hyphae act as a physical "highway" for these PSB to move beyond the rhizosphere into patches of insoluble phosphorus in the soil
• As a result, the resource-mobilization efficiency of the microbial community as a whole improves dramatically

In field trials of maize on saline-alkaline soils in China (BeiWuLao and XuJiaZhen), in plots that integrated AMF while reducing chemical fertilizer (AHCF), compared to conventional fertilization plots,

• Yield increased by 23.5% (11,475 → 14,175 kg/ha) up to a maximum of 81.2% (7,245 → 13,125 kg/ha)
• Available potassium (AK) in soil rose 77.7%
• Available phosphorus (AP) rose 33.9%
• Ammonium nitrogen (AN) rose 57.3%
• Soil organic matter (SOM) rose 96.4%

— a dramatic improvement in soil fertility was confirmed. It has been demonstrated that using AMF can cut the recommended chemical phosphate fertilizer application for crops by up to about 80%.

The "liquid carbon pathway" — root exudates, not residue

Jones's central claim is the "liquid carbon pathway." It is also an important correction to the agricultural science community.

Industrial agriculture has misunderstood, believing that soil carbon is maintained by tilling crop residues (above-ground biomass) into the soil.

But the result of Jones's analysis of 10 experiments showed:

In other words, what makes soil fertile is not dead plant residue but the liquid carbon compounds living plants produce by photosynthesis and exude through their roots.

Plants exude sugars, enzymes, amino acids, and other compounds produced through photosynthesis through the roots, and these become strong signals and food for soil microbes (bacteria and mycorrhizal fungi). Microbes use this liquid carbon as an energy source to dissolve nutrients such as inorganic phosphate tightly bound to soil minerals, and supply them to the plant.

Jones emphasizes that "plant diversity" is essential for this biological exchange to function. Industrial agriculture, growing a single crop with chemical fertilizer and fungicides, directly inhibits microbial activity and thereby drives farmers further into dependence on more expensive pesticides and fertilizers.

This means that modern soil ecology independently corroborates the "no weeding" principle Masanobu Fukuoka articulated — keeping living grass roots in the ground continuously — covered in Chapter 8.

Why "up to 90%"

In a natural state without chemical fertilizers, plants getting their nutrients via mycorrhizal fungi is far more efficient than absorbing them directly through their own roots.

Because:

• Hyphae are far thinner than roots and can enter the soil's tiny spaces
• The hyphal network is on a wholly different scale
• Mycorrhizal fungi have enzymes that solubilize insoluble phosphorus

Evolutionarily, plants chose the path of "outsourcing to mycorrhizal fungi" because it was efficient.

In natural conditions without chemical fertilizer, the lead actor in plant nutrition was the mycorrhizal network — not the roots.

5.3 Chemical fertilizer has been breaking the symbiosis

Here is an ironic fact.

Chemical fertilizer breaks the mycorrhizal symbiosis.

This is not a story about "overuse." It is the fact that the moment water-soluble chemical fertilizer is applied, the symbiotic circuit shuts down at the molecular level.

Closing the "carbon faucet" and the GA signal

The mechanism by which chemical fertilizer destroys the soil ecosystem is not direct toxicity, like a pesticide's. It is the "cancellation of an economic transaction" (ecological decoupling) between plants and microbes that had been operating at a sophisticated level.

The plant–mycorrhizal relationship is a mutual exchange of carbon and nutrients (phosphorus, nitrogen, and so on). However:

When high concentrations of water-soluble phosphate fertilizer or synthetic nitrogen fertilizer are scattered across the soil, the area around the plant's roots is temporarily overflowing with nutrients that can be absorbed directly without relying on the mycorrhizal network. When the plant's sensors perceive this excess nutrient state, the plant performs an evolutionary-chemical cost calculation. It judges, "if there are nutrients this easily absorbable around me, there is no need to spend precious energy (liquid carbon) handing it over to mycorrhizal fungi," and stops investing in the symbiosis.

This closure of the "carbon faucet" has had its detailed mechanism elucidated in recent molecular-biological research.

Normal symbiosis process:

1. The plant releases molecular signals from its roots, such as strigolactones and flavonoids
2. AMF hyphal growth is promoted
3. AMF produce "Myc factor" (a mixture of chitooligosaccharides and ribosaccharides)
4. Recognized at the plant cell membrane, calcium oscillations in and around the nucleus are triggered, activating the symbiotic pathway

Chemical fertilizer's blocking of the symbiotic circuit:

• When high concentrations of phosphate (Pi) are supplied, the plant itself blocks the symbiotic pathway via the plant hormone GA (gibberellic acid)
• Under high-phosphate conditions, GA biosynthesis levels rise in mycorrhized roots, acting as a powerful inhibitor of AMF symbiotic development
• In genetically modified tobacco lines that express GA methyltransferase to lower GA signaling, AMF colonization levels rise even under high-phosphate conditions has been demonstrated
• High-phosphate treatment does not immediately destroy already formed, finely branched arbuscules (the main nutrient-exchange sites), but it selectively inhibits "the development of new arbuscules"

In other words, when chemical fertilizer is applied, the plant senses "phosphorus is easily obtainable from outside," and to save energy (carbon) voluntarily shuts down the symbiotic circuit with AMF via GA signaling and the like.

The death of the network and "fertilizer addiction"

Arbuscular mycorrhizal fungi, which depend entirely on plant-derived liquid carbon as their energy source, are obligate biotrophs, so when the host's carbon supply is cut off, they cannot survive. As a result, the mycorrhizal fungi's activity slows, and over time the vast hyphal network dies and shrinks.

When the mycorrhizal network collapses, a fatal domino effect (a negative loop) propagates through the entire soil ecosystem.

1. Collapse of physical structure: with mycorrhizal fungi dying, the continuous production of glomalin — soil's adhesive — ceases. Soil aggregate structure gradually breaks down, the soil hardens (compaction), and drainage and air permeability deteriorate sharply
2. Loss of environmental tolerance: the water-collection system provided by hyphal networks hundreds to thousands of times wider than the root system is lost, leaving plants extremely vulnerable to drought
3. Trace-element deficiency and falling nutrient density: chemical fertilizer supplies major elements such as N, P, K in bulk, but the mycorrhizal system that gathers diverse trace minerals such as zinc, copper, magnesium, and cobalt from a wide range is lost. As a result, the crop may grow large in appearance while internal mineral density (nutrient value) drops sharply — the "empty calorie" effect advances
4. Fertilizer runoff and immobilized legacy phosphorus: the soil's retention functions (aggregates and microbial biomass) are lost, so most of the heavily applied fertilizer does not stay in the soil and flows into groundwater and rivers, causing serious water pollution (eutrophication). At the same time, the means for solubilizing the enormous "legacy phosphorus" immobilized in the soil by phosphatase enzymes is also entirely lost, and farmers must keep buying expensive water-soluble phosphate fertilizer every year

A soil that has been on chemical fertilizer for years to decades like this falls into a state of severely impoverished microbial flora and physical degradation. In this state, the soil environment has been optimized for microbes "not to work."

When you use chemical fertilizer, the plant itself sends the signal to soil microbes: "you are no longer needed." As a result, the microbes are out of work and disappear from the soil. That is why a state arises in which "without chemical fertilizer, the crop won't grow at all." This is by no means natural law — it is the result of a self-fulfilling "withdrawal symptom" produced by the structure of dependence on chemical fertilizer itself.

If you stop chemical fertilizer all at once, yields drop for the first few years. It takes time for the soil ecosystem to recover.

Conversely: with time, it does recover. Mycorrhizal fungi return as long as living roots are there (as noted, AMF are obligate biotrophs, so living roots are essential).

5.4 The misconception that "natural farming is spiritualism"

Let me emphasize an important point here.

When this series says "migrate to natural farming," it is not based on

• The philosophy of "respect for the wisdom of our ancestors"
• The aesthetics of "harmony with nature"
• The norm of "organic is correct"

Rather, it is based on:

• Chemical fertilizer rises in price (economics)
• The accounting of industrial agriculture breaks down (economics)
• The soil already has phosphorus (physics)
• Microbes can mobilize it (biology)
• Chemical fertilizer was stopping the microbes (biology)

— from these facts of economics, physics, and biology, microbe-based farming is what remains by elimination.

It is not "live in harmony with nature." It is "let microbes stand in, because we won't be able to buy chemical fertilizer."

This is not spiritualism — it is a story of accounting and physics. And so, independent of whether you sympathize with organic farming or hold any naturalist faith, the conclusion follows: only this direction is economically viable.

But human knowledge has limits — learn from 500 million years of evolution

Here a very important caveat must be added.

The conclusion "microbe-based farming," derived from facts of economics, physics, and biology, is the most coherent answer within what humans currently know. But it is not necessarily the right answer.

What humans know about nature is only a small part.

Land plants have a history of about 500 million years.

• 475 million years ago: plants moved onto land (covered earlier in this chapter)
• Since then, through countless trial and error, enormous diversity has emerged
• Millions of plant species, tens of millions of microbial species, and the ecosystems they weave
• For each region, each climate, each soil, "the answer that holds there" has evolved on its own

Against this 500-million-year accumulation of evolution, human scientific knowledge has only about 150 years of history. Discoveries such as the function of AMF, the liquid carbon pathway, and glomalin are stories of the last 30 years.

Concluding "microbe-based farming" from facts of economics, physics, and biology is the most coherent answer at present. But it is only the optimum within the range humans know. Nature itself knows much more.

Diversity is the answer of 500 million years

What 500 million years of evolution produced is not a single "correct answer." It is an enormous number of locally balanced solutions combining region, climate, soil, microbes, plants, and animals.

• Tropical rainforest ecosystems
• Temperate deciduous forest ecosystems
• Volcanic ash soil (Andisols) ecosystems
• Wetland ecosystems
• Terraced rice field ecosystems (made by humans, but already thousands of years old)
• Secondary-forest ecosystems of satoyama

All of these are separate answers optimized for their place. When this series says "migrate to microbe-based agriculture," it does not mean unifying everything to a particular form.

The answer 500 million years of evolution gave is diversity itself. Each region, each field, each household — learning from nature's diversity and finding their own answer — that is the proper picture.

"Deduction" alone is not enough — observation is required

Deductive reasoning from economics, physics, and biology is sufficient to indicate direction. But in the actual field, observation and trial and error are equally important.

• Look at your own field carefully
• Listen to the behavior of plants and microbes that have 500 million years of history
• Don't apply textbook answers; learn what is happening in your land
• Learn from failures; adjust
• Respect diversity

When Masanobu Fukuoka arrived at the principles of "no weeding, no tilling, no fertilizer, no pesticide," it was not from deduction but from observation and practice. His four principles have since been backed up by scientific research (as we saw in this chapter) — but he did not start from scientific facts; he started from observing nature.

The direction shown by economics, physics, and biology is probably right. But to implement that direction, the humility to learn from nature itself is required. Diversity with 500 million years of history cannot be replaced by 150 years of science alone.

The logic this series presents is a first sense of direction. When you actually move with it, you must observe your own land, your own climate, your own microbial flora, your own crops carefully, and find your own solution while respecting the diversity that 500 million years of evolution shows.

Delegating farming to AI overlooks a double limitation

Here let me add one more important caveat. In recent years, "AI-driven precision agriculture" — integrating satellite imagery, drones, soil sensors, and AI analysis — has sometimes been spoken of as the savior of agriculture.

But AI has an essential limitation.

AI has only learned from books and the internet — text.

AI is

• not directly touching the soil
• not directly looking at plant roots
• not directly observing the mycorrhizal hyphal network
• not directly feeling the microclimate or water veins of that field

What AI "knows" is limited to what humans have written down up to now. Further: it is limited to what has been digitized and exists on the internet.

In other words,

AI is merely organizing, summarizing, and combining what 150 years of human science has recorded. Most of the diversity 500 million years of evolution produced has not been recorded by humans. What is not recorded, AI does not know either. AI is a "copy of a copy" of human knowledge — not a primary observer.

A double limitation

To elevate "AI-driven precision agriculture" to be agriculture's final arbiter overlooks a double limitation.

• First limitation: human science itself is only 150 years against 500 million years of evolution
• Second limitation: of that 150 years, AI only knows the part that has been written down and digitized

Much of traditional farming wisdom — for example, the decades of observation through which Fukuoka arrived at "no weeding," local indigenous farming methods, the bodily sense required to maintain terraced rice fields — has been neither published as papers nor digitized. There is currently no way for AI to learn it.

In addition, the specificity of each field — where water tends to pool, which slopes catch the sun, where animal trails run, what weeds grow where and how — is living information that changes year by year, day by day. This too is impossible for AI to learn in advance.

Use AI as an "assistant"

This is not a "don't use AI" story. This site (aiseed.dev) runs in parallel a series "AI-native ways of working" that recommends using AI as a "colleague." AI is

• organizing and summarizing literature
• aggregating and visualizing data
• reminders for seasonal work
• early warning of pests and diseases (image recognition)
• question-answering that draws out existing knowledge

— extremely useful as an assistant.

But:

It is wrong to entrust the final agricultural decision to AI. AI has only learned from what humans have written. It is not directly looking at soil, plants, or mycorrhizal fungi. Touching your own soil, observing plants, listening to the behavior of microbes — none of this can be substituted by AI. AI is the assistant; the final call is made by a flesh-and-blood human, observing 500 million years of nature — that is the right way to use it.

If you place precision agriculture or AI analysis at the "destination," then on top of the supply-chain trap (Chapter 3), you are also locked inside the epistemological trap of "the range of human written knowledge."

Tools are tools. Judgment is made by a human in direct dialogue with nature.

5.5 The method that remains by elimination

Let me organize. What disappears, and why?

What remains is:

• Maintain domestic production as much as possible
• But by methods that do not depend on chemical fertilizer
• Use the phosphorus already in the soil and the soil microbial network
• Cover the shortfall with imports

This is the elimination conclusion.

5.6 Selecting resilient crops — minimize input resources

To run the biological-mining architecture cost-efficiently, beyond the mycorrhizal network, the choice of crop itself is decisively important.

Precision agriculture and industrial agriculture have presupposed varieties whose performance only emerges when humans pour in massive management resources — the F1 hybrid varieties being the representative case (covered in detail in Chapter 7). Biological mining, by contrast, can minimize human and material input by choosing

• crops with the vitality of weeds
• indigenous varieties with high environmental adaptability and open-pollinated reproducibility
• crops that can be deployed at scale by direct seeding

Examples of resilient crops

In particular, Trombetta di Albenga (Trombetta squash, an elongated zucchini/squash originating in Italy):

• bears 10–30 fruits on a single vine even on weed-overgrown wasteland
• maintains stable traits even when seed-saved
• has high pest and disease resistance and can be grown without pesticides
• the young fruit (as zucchini) and mature fruit (as squash) are both edible
• stores for long periods (months to half a year)

— a typical example of a crop optimal for the biological-mining architecture.

A "plant and wait" system

Deploying these resilient crops with diversity, in mixed direct seeding, makes the following system possible:

• Sow seeds (or plant seedlings)
• Minimum protection if needed (e.g., against animal damage)
• Management close to leaving alone until harvest

There is no need to monitor sensors daily and calculate inputs, as in precision agriculture.

What achieves "the cost structure with the least waste" is not adding complex control, but combining crops with autonomous vitality and the soil microbial network that supports them.

As we will see in Chapter 6, rising CO2 concentration acts as a tailwind for this autonomous system. Conversely, industrial agriculture, premised on chemical fertilizer, pesticide, and F1 varieties, faces the paradoxes of "nitrogen depletion" and "hidden hunger" under rising CO2 (see Chapter 6).

5.7 So how do you actually run it?

"Have microbes stand in" — concretely, what do you do?

This is the theme of the second half of this series — Chapters 7 and 8. The concrete principles are:

• Don't till (so as not to break the microbial network)
• Don't make bare soil (to preserve soil temperature and moisture and protect microbes)
• Grow diverse plants (to support diverse microbes)
• Don't use chemical fertilizer or pesticide (so as not to kill microbes)
• Don't let living roots disappear (mycorrhizal fungi can only receive nutrients from living roots)

There is one point here that is easily misunderstood.

In Japan, Masanobu Fukuoka's natural farming has held no weeding — not cutting weeds — as a principle. By contrast, in regenerative agriculture overseas, grass mulch and cover crops are sometimes recommended.

How should this difference be understood? Chapter 8 covers it in detail. Just to summarize the gist:

What mycorrhizal fungi need is "living roots." Cut grass laid on the ground does not become a nutrient source for mycorrhizal fungi. Fukuoka's "no weeding" is consistent with the principle of mycorrhizal symbiosis in that it keeps living roots from being severed.

This is the point at which traditional natural farming and the latest soil science are, in the end, saying the same thing.

5.8 Summary of Chapter 5

• The soil already holds enormous phosphorus (cumulative chemical fertilizer)
• The accumulated phosphorus is in a form (insoluble) plants cannot absorb
• Mycorrhizal fungi solubilize insoluble phosphorus and supply it to the plant
• Up to 90% of the nutrients a plant needs can be obtained via mycorrhizal fungi
• Chemical fertilizer has been breaking this symbiotic relationship
• If you stop using chemical fertilizer and keep living roots in the ground, the symbiosis recovers
• This is not spiritualism — it is derived from facts of economics, physics, and biology

The next chapter looks at one more tailwind fact: rising CO2 concentration boosts plant growth. Climate change is often described in negative terms, but for agriculture there are also unexpected positives.

Looking at the relationship between CO2 and soil microbes, you can see that now is a rare opportunity to migrate to microbe-based agriculture.

References

Mycorrhizal fungi and soil microbiome science

• Christine Jones, "Light Farming: Restoring Carbon, Organic Nitrogen and Biodiversity to Agricultural Soils" (2018) — the liquid carbon pathway, soil-stabilization rates of 8.3% (above-ground) vs 46% (root exudates)
• "Mycorrhizal Fungi Explainer and Definition" — Society for the Protection of Underground Networks (SPUN) — 475 million years of evolution; 4.5 quintillion km of fungal hyphae globally
• "Mycorrhiza: The Hidden Plant Support Network" — USDA NRCS
• "A phosphorus threshold for mycoheterotrophic plants in tropical forests" — PMC NIH (about 80–90% of land plants form mycorrhizal symbioses)
• Sara F. Wright (USDA-ARS) — discovery of glomalin and its contribution to soil aggregate structure
• Kristine Nichols — glomalin secretion from AMF hyphae
• Plantae plant database — literature on the non-mycorrhizal families Brassicaceae and Amaranthaceae (Chenopodiaceae)

Legacy phosphorus

• "Farmers are facing a phosphorus crisis. The solution starts with soil." — National Geographic
• "USDA Legacy Phosphorus Assessment Project" — Natural Resources Conservation Service
• "The Occurrence of Legacy P Soils and Potential Mitigation Practices Using Activated Biochar" — PMC9238423
• "Evaluation of Phosphorus Enrichment in Groundwater by Legacy Phosphorus in Orchard Soils" — ACS Publications, acs.est.3c07170
• "Characteristics of Organic Phosphorus Pool in Soil of Typical Agriculture Systems in South China" — MDPI 2311-7524/8/11/1055
• "Phosphate binding to allophane and ferrihydrite with implications for volcanic ash soils" — ResearchGate (Andisols, Japan's kuroboku volcanic ash soils)

Plant uptake rates and fixation mechanisms of chemical fertilizer

• "A new perspective on the efficiency of phosphorus fertilizer use" — IUSS 19th WCSS Symposium (10–25% same-year recovery, wet-process method)
• "A review on phosphorus drip fertigation in the Mediterranean region" — PMC10850969
• "Which method for calculation of fertilizer phosphorus use efficiency is better?" — ResearchGate
• Technical literature on the absorption rate and manufacturing process of fused phosphate fertilizer

AMF + PSB synergy and demonstration data

• Maize AHCF field trials on saline-alkaline soils in China (BeiWuLao and XuJiaZhen) — yield +23.5–81.2%, fertilizer reduction potential of 80%
• "Mycorrhiza: a natural resource assists plant growth under varied soil conditions" — PMC7165205
• Microbiology literature on the synergistic consortium of phosphate- solubilizing bacteria (PSB) and arbuscular mycorrhizal fungi

Molecular mechanisms of symbiosis inhibition by chemical fertilizer

• Molecular biology literature on the shutdown of the AMF symbiotic circuit by GA (gibberellic acid) signaling
• Research on activation of the symbiotic pathway by strigolactones, Myc factor, and calcium oscillations
• Research on rising GA biosynthesis under high-phosphate conditions and inhibition of AMF colonization

Resilient crops

• Horticultural literature on the cultivation characteristics of Trombetta di Albenga, the elongated squash originating in Italy
• Local case reports on the low-input suitability of indigenous potatoes, indigenous root crops, and traditional grains

Green chlorite schist and alluvial silt

• Geological literature on mineral supply from weathered green chlorite schist
• Soil science literature on agricultural mineral supply from alluvial silt