Soil Fertility is Not Bought
It Is Built, Grown and Protected

Most soils already contain everything plants need. What’s missing is not fertiliser, but space, air, water, and biological life. When soil biology is given the right conditions, fertility builds itself—quickly, safely, and permanently. This page explains how Keyline cultivation and the Yeomans Plow accelerate a natural process that has always been the foundation of productive farming.

What “Creating Fertility” actually means

When we say “create fertility”, we’re not talking about buying nutrients and adding them. We’re talking about turning biologically inactive subsoil into living, humus‑rich topsoil — and doing it fast.
In Yeomans terms, the cash value of soil comes down to two things:
  1. Basic mineralisation (set by geology — you can’t change it much)
  2. Humic content (the amount, age and stability of humic substances — you can change this a lot through farming)
That second factor — humus/humic substances — is where real, lasting fertility lives.

Why deep tilling matters: “space” is the missing ingredient

Healthy soil is a habitat. Soil life needs:
  • air to breathe
  • moisture
  • food (dead plant material and dead roots)
  • space to live
In many paddocks the big limiting factor isn’t “lack of fertiliser” — it’s lack of space, because subsoil has become dense and closed (hardpan / compaction). When that happens:
  • water infiltration is limited
  • roots are restricted
  • air movement is poor
  • soil organisms can’t thrive in numbers
Deep tillage (subsoiling) works mechanically because a narrow shank penetrates to depth, lifts the soil like a wedge, and the lifting action causes the compacted layer to fracture and crack — creating loosened, aerated subsoil.
Keyline cultivation takes that same basic “fracture the subsoil” idea, but aims to do it with minimal soil profile disturbance so biology can explode without the penalties of mixing layers.

What the Yeomans Plow is doing in the ground (the critical difference)

A Yeomans pass is not meant to churn soil or flip layers. The point is:
  • During cultivation the soil is gently lifted and loosened
  • with negligible soil profile disturbance
  • so rain is rapidly absorbed and air becomes readily available
A simple farmer‑check for correct operation is: “The plow is working perfectly when you see the ground rise up around the shank and then gently settle back to not quite where it was before.”
That “lift and settle” is a visual sign that you’re creating fracture and porosity, not turning soil into loose surface rubbish that seals over again.
And this matters because the microbes and fungi that create humus are aerobic (they breathe air). If soils are saturated after heavy rain, “soil life is drowning” — and the fastest fix is to restore air pathways.

 

The fertility chain reaction (what happens after you open the soil)

Once deep tilling creates air and space, a biological and chemical chain reaction begins.

Water goes in, not away

With soil opened and fractured:
  • storm rains infiltrate into the deep worked soil
  • storm erosion and wash can vanish
  • the paddock holds rainfall rather than shedding it
This is not just a water benefit; it’s the start of the fertility engine — because moisture and air are now present together where biology lives.

Soil life multiplies (fast) if it has food

“It all starts with dead plant material, air and water.”
When you’ve opened the soil and there is dead root material and surface litter available:
  • bacteria, fungi, actinomycetes, and worms feed
  • they multiply
  • they die and are consumed in turn
This is the manufacturing line that turns residue into humus.

Biology makes the “key” chemicals that unlock minerals

As soil life processes organic matter, it produces concentrated acids that break down tiny rock structures and release crucial elements. Minerals that are “unavailable” to plants can be made available through healthy soil biological activity — and if that weren’t true, land plant life could not exist.

Minerals get “shelved” onto humic substances (so they don’t leach)

Once released, those minerals don’t just float away. They:
  • minerals chelate / loosely attach onto clay particles and humic acid molecules
  • chelated this way, they are insoluble in water but still available to growing plants
This is the practical reason humus matters: it holds nutrient in the root zone while keeping it plant‑available.

Humus forms (and soil structure starts to “feel right”)

As the biology continues, complex humic substances form:
  • “Complex humic acid molecules are ultimately formed.”
  • Long sugar‑like chains (polysaccharides) form and bind soil
  • fungal thread‑like structures bind soil particles
  • small aggregates accumulate, which you feel as “good soil structure” in your hand
This is where your deep tillage pass becomes more than “loosening”. It becomes soil making.

Two kinds of humus explain why fertile soil feeds crops safely

  • Dauerhumus: long‑lived humus that does not itself form part of biological activity
  • Nahrhumus: short‑lived, biologically active humus (minutes to months) that gets broken down and releases “a constant, harmless trickle of ammonia” to fine roots
And the key agronomic consequence:
“Almost all of the nitrogen supplied to plants in healthy soil is derived from this organic material within the soil.”
So you end up with a system that stores minerals, supplies nitrogen gently, and builds structure — without reliance on inputs that destroy the biology doing the work.

Worms move in, field capacity rises, rainfall becomes less critical

As organic content rises:
  • earthworms establish
  • their casts become a rich source of humus
  • their slimes/glues enhance structure
  • the soil’s ability to retain moisture (“field capacity”) rises dramatically
  • rainfall patterns become less critical to the farmer
That is the real “water security” story in Keyline: it’s not just storage — it’s soil becoming a sponge through structure and humus.

 

Practical operating rules that directly support fertility building

Deep tilling only creates fertility quickly when it’s done in a way that supports biology and avoids destructive mixing. Here’s a practical guide which farmers can apply:

Start timing (don’t wait for “soft soil” out of habit)

  • “Plow Immediately. The day it’s delivered.”
  • cultivate so the next rains are retained

Spacing (a broad starting point)

  • shank spacing “around half a metre or 20 inches” to get going
  • pasture guide: “20” to 32” apart”

Depth (especially where there’s a hardpan)

  • if previously cultivated, dig down and find the old hardpan
  • then set depth “about 2” to 3” (50–75mm) under the hard pan”

What you don’t want to see (slabbing)

  • if hard pans come up “like slabs of broken concrete”, fit a crumble roller to cut/flatten clods and speed the formation of fertile soil

Why extreme depth isn’t always the win

  • there’s “no great commercial advantage” cultivating much over ~14” (350mm), except in badly leached soils “where you are chasing minerals”

A Keyline principle about roots (depth that biology will actually use)

  • if you cultivate at extreme depth before the root mass is ready, the soil can “close up within a year or so”
  • and that depth should relate to “the depth of vigorous root activity… go a few inches below this” so roots are happy to move down
That’s a crucial point for farmer understanding: deep tillage is not just engineering — it’s engineering in service of root and biological progression.

 

The simple summary farmers remember

Farmers can do one thing better than nature ever can:

Create space in the soil instantly

One correct deep pass with a Yeomans Plow:

  • Opens compacted subsoil
  • Lets air in
  • Lets water soak deep
  • Gives soil life somewhere to live

This speeds up soil creation hundreds or thousands of times. What took centuries can happen in a few seasons.

“There is almost no agricultural problem that cannot be solved by increasing soil fertility”
Allan Yeomans