How you take a census of something you cannot see
Thirteen cores of soil, taken from under five different plants growing in the same pasture. From each core we pulled out all the DNA at once — the plants', the worms', the bacteria's, everything mixed together.
Then we photocopied one particular gene, called 16S, millions of times. Every bacterium carries it and no plant or animal does, so copying it is how we ignore everything that is not a microbe. A sequencing machine reads those copies, and matching them against a reference library turns them into a list of names and counts.
Out of thirteen samples came distinguishable kinds of bacteria and archaea, from between and DNA reads per sample.
Worth knowing: this counts DNA, not bodies, and not activity. A microbe that is dormant, or dead but not yet decayed, still shows up — and in soil the dead share is not small.
Every patch is equally rich. They are not the same patch.
The obvious first question is whether some plants host more life than others. They do not. Diversity is statistically flat across all five plants (p = ), and flat again under a second measure that accounts for how closely related the organisms are (p = ).
Each dot is one soil core. The bar is that plant's average.
But that is the less interesting half. When you stop asking how many and start asking which ones, the patches separate by the plant growing above them.
Cores that contain similar communities sit close together. The two directions are the largest and second-largest ways these samples differ — they carry % and % of all the variation.
The plant explains meaningfully more of that separation than chance would. Because there are five plants and only thirteen cores, pure chance already produces an apparent effect of about — so the honest measure is not the raw but the of it that chance does not explain (p = ).
Two follow-up checks. It is not driven by one patch being unusually varied while the rest are tight — the spread is even across plants (p = ). And it survives a completely different way of measuring how different two communities are, one that counts how distantly related the organisms are rather than just how many they share (p = ).
Same amount of life everywhere. Different life everywhere. The plant above picks the neighbours below.
The analysis shuffled the plant names across the cores times and recomputed the effect each time. Every grey bar is how many of those shuffles landed at that value. Press the button to pull one out.
What a press actually does. It draws one value from the shuffles the analysis already ran, whose distribution is what the grey bars are. It does not re-run the test in your browser — that would need the whole distance matrix here and would be a different procedure from the one the manuscript reports. You are sampling the real null, not simulating a new one.
The headline: to 1
Turning ammonia into nitrate is one of the essential jobs in any soil — it is most of what "nitrogen cycling" means. Two very different kinds of life can do it: ordinary bacteria, and archaea, an ancient and completely separate branch of life. Which of the two dominates says a great deal about a soil's history.
In this pasture the archaea outnumber the equivalent bacteria by roughly to one (% of all the DNA read, against %). Heavily fertilised soils tend to flip this: the bacteria are the ones that bloom on a flush of synthetic nitrogen. A ratio this lopsided towards archaea is the signature of soil that has not been getting that.
How do we know the list of archaea is right?
That headline depends on a hand-built list of which organisms oxidise ammonia, so it is fair to ask who built the list. We re-ran the same samples through an independent published database that was assembled by other people for other reasons. It puts ammonia oxidation at % where our list says %, and nitrogen fixation at % against our %. Two unrelated methods, the same answer.
But couldn't the soil just be sour?
There is an obvious objection to everything above, and it is the one a sceptical scientist would raise first. Archaea also take over from bacteria in acid soil — nothing to do with farming. Public soil maps put this ground at around pH 5.5, which is firmly on the acid side. So perhaps the headline is not a story about management at all. Perhaps it is just geology.
The archaea answer this themselves, because they are not all alike. One group of them can only live in acid — put it in ordinary soil and it dies. The other group prefers ordinary soil. If sour ground were the reason this pasture is full of archaea, the acid specialists should be a large share of them.
They are % of the archaea here. The ordinary-soil group outnumbers them roughly to one (% of all DNA read, against %).
Acid soil alone does not explain it. These are not the archaea an acid soil would select.
There is a second way at this, and it does not use our sequences at all. Nobody has measured the acidity of this field — but two research stations within km have been sending soil to a laboratory for a decade, and between them they have measurements. If the maps are right about this neighbourhood, those measurements should sit around the modelled value.
The dashed line is what public soil maps estimate for this farm. The bars are measured samples from the two nearest research stations: the box is the middle half, the line inside it the median, the whiskers the full range. Measured in a .
They do not. The nearer station's median is and the further one's is — the modelled prior for this farm falls of a unit below the nearest of them, and outside the middle half of both. Less acid, in other words, than the maps had this ground.
Which cuts the same way. The rival explanation needs this soil to be sour; the archaea living in it say it is not, and the nearest real measurements say the estimate that made it sound sour is probably too low.
These are not this field. They are the closest measured soil, twelve and sixteen kilometres off, and one of the two is under woodland — soil pH turns over across a single hillside, and the range on the chart shows it doing exactly that. This does not establish the pH here. It establishes that the number the acid explanation leans on is a model's guess, and that where anybody has checked nearby, the guess reads low.
What this does and does not do. It weakens the simplest rival explanation; it does not prove the management one, and it is not a substitute for actually measuring this soil's acidity, which still has not been done. Reading which organisms are present also tells you who is there, not how hard they are working.
Clover changes the neighbourhood
Clover makes its own nitrogen fertiliser, using bacteria housed in nodules on its roots. If some of that nitrogen leaks into the surrounding soil, the ammonia-oxidising archaea nearby should have less work to do — and should be less abundant. That is what the samples show (p = ).
Each dot is one core. Orange cores were taken under a legume — red or white clover, the plants that make their own nitrogen.
A food web, not a soup
A second set of DNA reads, tuned to pick up organisms with more complex cells, shows this is not just a bag of bacteria. There are fungi, there are protists that hunt and eat bacteria, and there are microscopic animals — nematodes and mites — that eat the protists. Predators are present, which means the system is running, not merely present.
Share of the complex-celled organisms in each patch. Based on of the thirteen cores — this second test was not run on all of them.
What we cannot say yet
The clover pattern above is real. But we tested whether it is specifically about nitrogen, and it is not. Of common bacterial groups, track the archaea about as closely as the nitrogen-fixers do, and the nitrogen-fixers rank only among them.
What is actually happening is simpler, and we can show it directly. The whole community shifts along one dominant gradient — the horizontal direction in the second chart on this page, which alone carries % of all the variation between cores. The archaea ride that gradient (correlation , p = ). They are not responding to one neighbour. They move with everything at once.
So we can say the archaea differ by plant. We cannot yet say why.
And one more: only a single white clover patch was sampled. One is not a group, and nothing here should be read as a finding about white clover specifically.
The headline counts two competitors, and there is a third. Some bacteria do the whole ammonia-to-nitrate job by themselves rather than handing it over halfway, and they are especially good at it when there is very little ammonia around — which is what we think is the case here. The kind of DNA reading used for this study cannot tell them apart from a close relative that does an unrelated job, so we can only say their combined share is %. That is small, but it is not nothing, and it means the headline ratio compares the two best-known ammonia oxidisers rather than every organism doing the work.
Compared with other farms
A published study sampled organic and conventional pastures the same way. Set beside them, this soil has far more archaea and far more of the group that tends to dominate undisturbed ground.
Each dot is one soil sample. The bar is the group average.
Read this one carefully. That is a different farm, in a different place, with soil processed in a different laboratory — any of which can move these numbers on its own. And the sharpest test cuts against the comfortable reading: within that published study, organic versus conventional management made no detectable difference to either measure (p = and ). If management alone did not move the needle there, it cannot be the whole explanation here. This soil is unusual. Why it is unusual is not settled.
And against the field next door
Every comparison so far has been with soil somebody else sampled. There is one that does not need a laboratory at all: satellites have been photographing this field, and the fields around it, every few days for years. From those pictures you can measure how green a parcel is, and — more usefully — whether it stays green.
That second one is the claim regenerative management actually makes. Ground kept under continuous living cover should not swing between lush and bare across a season. Ground that is tilled, or cut and left, should. It is a prediction about steadiness, not about peak greenness, and the two come apart here.
Each point is one parcel across cloud-free satellite passes. Right is greener. Down is steadier — less change between one pass and the next.
The farm is greener than % of the parcels around it, which is to say: not very. It is steadier than % of them, and it is the only parcel that never once dropped below the bare-soil line in passes.
Cover that persists, not cover that peaks. Which is the shape the claim predicts — and notably not the shape a fertiliser would produce.
Nobody has checked what those neighbours do. They are fixed boxes on a ring around this field, not mapped property lines, and no one has established that a single one of them is conventionally farmed — they are simply the nearest ground. Eight of them is far too few to test anything, and there is deliberately no line drawn through those points and no p-value quoted, because neither would mean anything. This situates the farm. It does not explain it, and it cannot connect the satellite picture to the archaea underneath.
What would settle it
Three things, none of them exotic. A measurement of this soil's acidity, which drives the archaea-to-bacteria balance nearly as strongly as nitrogen does. The archaea themselves already argue that acidity is not the whole story, but that is an inference, and a pH meter would be an answer.
A comparison against soils that received known, deliberately different amounts of nitrogen — if the ratio moves with the nitrogen, the mechanism stops being a story and becomes a result.
And a test of a different idea entirely. Some plants release compounds from their roots that shut down ammonia oxidisers directly, and how strongly they do it varies between grasses and clovers — exactly the comparison this farm happens to offer. If that is what is happening here, the clover pattern is not about nitrogen at all: it is the plant switching the archaea off. Testing it means washing the roots and seeing whether what comes off them stops the reaction in a dish. That is bench work on plants already growing in this field.