Soil Carbon:
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The Natural Farmer
S u m m e r, 2 0 1 4
Some Frequently Asked Questions
by Dr. Christine Jones
Q: Is it fair to say that carbon is the key ingredient
that makes the difference between barren, unhealthy
soil and fertile, healthy soil?
A: Yes. The glues and gums that hold soil particles
together in the form of aggregates (small lumps)
are made from carbon. Aggregation is what gives
soil its tilth - making it well-structured, porous and
friable. Porosity, in turn, improves the infiltration
and storage of water. Carbon derived from plants
also provides the energy for the soil biota essential
to nutrient availability. Plants give to the soil, rather
than take from it, as many people believe. The
greatest threat to soil health is bare ground. When
soil lies in bare fallow for long periods (eg. between
crops) - or if it is over-grazed and has bare patches it will deteriorate. Around 80-90% of plant nutrient
acquisition is microbially mediated. If there’s no
energy for the microbes (in the form of carbon)
there will be very little nutrient - particularly vital
trace elements - for plants. These deficiencies are
passed along the food chain to animals and people.
Q: When did humans begin to release carbon into
the air through disruption of the soil? Can you
explain the process of how this happens?
A: As soon as living plant cover is removed,
soil begins to deteriorate. Plant litter (mulch)
can maintain the condition of the upper layers
of soil (topsoil) but cannot maintain the deeper
layers (subsoil). There must be active root growth
in subsoil in order for it to remain alive and
functioning effectively. Grasslands build more
soil - and deeper soil - than forests. Due to these
deep, carbon-rich soils - and low numbers of trees -
grasslands were traditionally the areas first selected
for cropping. However, the removal of the actively
photosynthesizing year-round groundcover caused
immense damage - not only to subsoils - but also to
topsoil through wind and water erosion. Fortunately,
this damage can be repaired by restoring the flow of
liquid carbon via year-round living cover - such as
obtained with the use of multi-species cover crops.
Best results are seen when cover crops contain
at least 20 different varieties of plants and are
strategically grazed.
Q: Do you know when scientists first became
aware of carbon loss from soil, and of the possible
relationship to climate?
driver of soil health. It was in the early 1900s that
most of the significant research on humus occurred.
A lot of the information was discarded, however,
with the dawning of the ‘chemical age’ in the 1940s.
The destruction to soils (and the deterioration in
food quality) caused by synthetic fertilizers was
recognized even as early as 1948.
I don’t know when scientists first
discovered the relationship between soil carbon
and climate change. Professor Rattan Lal was
certainly one of the pioneers in this field (Lal, R.,
Kimble, J.M., Follett, R.F., Cole, C.V., 1998. The
Potential of U.S. Croplands to Sequester Carbon and
Mitigate the Greenhouse Effect. Ann Arbor Press,
Ann Arbor, MI, 128 pp.). I was the first scientist to
hold a conference specifically on the subject of the
A: In ancient times (as far back as the Roman
relationship between soil carbon and climate change
Empire, and possibly before), the word ‘humus’ was in the Southern (and possibly also the Northern)
used to refer to what we would call ‘soil carbon’
Hemisphere.
today. Although the actual composition of humus
was not known, it was well recognized as the main
Q: Do you endorse Allan Savory’s methods? What
determinant of soil fertility (soil ‘fatness’ was the
are other effective methods for restoring carbon to
general term used for soil health back then). The
soil?
first explanations of what humus might actually
be composed of began appearing in the scientific
A: Any method that increases photosynthetic
literature in the 1600s and 1700s. One hundred
capacity and photosynthetic rate will restore carbon
years previous, Flemish physician Jan van Helmont to soil - provided the flow of carbon is not inhibited
(1579-1644) discovered that the growth of plants
by chemicals such as synthetic nitrogen, water
did not reduce the weight of the soil. He was
soluble phosphorus - and of course pesticides and
puzzled as to the source of the plant material. If not fungicides. Holistic Planned Grazing is an effective
from the soil, how did plants grow?
way to increase photosynthetic capacity provided
Another two hundred years passed before
the land manager can accurately determine plant
scientists discovered the miracle of photosynthesis
recovery and adjust stock movements to match
(carbon fixing by living plants). Plants are
carrying capacity. In farmed lands where livestock
autotrophic, that is, they build themselves from light may not be an option, multi-species cover cropping
and CO2. We now understand that this carbon-fixing is effective - again, provided the inputs of synthetic
process - and the translocation of a portion of this
chemicals are reduced.
fixed carbon to soil microbes in liquid form - is the S u m m e r, 2 0 1 4
Q: What has happened so far in Australia, in terms
of individuals and groups taking action, as well as
government activity? Is Australia a pioneer in this
realm? What is happening in other countries?
A: Any attempt to verify soil as a carbon sink has
been blocked by the chemically-funded scientific
organizations in Australia. There are countless
documents from departments of agriculture and
universities which ‘prove’ that it is not possible
to increase the level of carbon in agricultural
soils. Despite the volume of expert opinion to the
contrary, however, I could take you to many farms
where soil carbon has been significantly increased.
Q: Can the earth’s soil sequester just the carbon
it previously lost, or can it also actually absorb
additional carbon from fossil fuel emissions? If the
latter, how does that work? Is the soil’s capacity to
absorb carbon limitless?
A: The soil’s capacity to sequester carbon
is determined by plant root depth and plant
photosynthetic rate. We know a lot more about those
things now than we did in the past. Photosynthesis
accounts for only a tiny fraction of the light energy
that comes to earth each day. If we could figure
out how to increase photosynthetic potential and
channel more of that energy to soil (as liquid
carbon), we could turn every farm into a net carbon
sink rather than a net carbon source. That would
be great for farmers and unbelievably good for the
planet!!
Soil building takes place downwards into
the soil profile. That is, as soil health is restored,
the soil becomes deeper and deeper. We are finding
plant roots at incredible depths on carbon-friendly
farms, so I certainly believe we can put all the
carbon back that has been lost. Whether we can
sequester sufficient carbon to mitigate the ongoing
emissions of fossil fuel remains to be seen. Biologyfriendly farm practices require far less fossil fuel
- and also result in fewer emissions - hence the
changed land management of itself will reduce the
problem to some extent. The Natural Farmer
Q: Do you see this movement to focus on soil
growing? What has surprised you the most in your
work on this issue?
A: From what I’ve seen in my travels around the
world, the impetus for soil building is coming
from farmers, ranchers and their advisors, rather
than from government. Change is being driven by
the fact that many farmers are no longer making a
profit. Once soil carbon stocks have been depleted,
no amount of synthetic fertilizer can maintain yield.
There is also an increasing desire on the part of
many farmers to reconnect with their land. This vital
connection has been lost in the industrial farming
model. I don’t believe there’s a farmer on the planet
who wants to use more chemicals or destroy soil
or make people sick. But sadly, that’s what many
are being driven to do. It concerns me that there is
neither support nor direction from government to
help turn this situation around. There are so many
good reasons for improving soils. Applying simple
techniques to increase the level of soil carbon will
make farming infinitely more enjoyable as well as
more productive - and vastly improve the quality
of our food. If governments provided financial
incentive for soil restoration, they would not need to
invest anywhere near as much in hospitals.
Q: Is stable soil carbon the same thing as soil
organic matter (SOM)? If not, could you elaborate?
Is stable soil carbon inorganic? Does SOM contain
carbon? Can both help mitigate climate change?
Can SOM eventually turn into stable soil carbon?
A: SOM is derived from plant material, animal
remains, compost, manure etc. - i.e. stuff you can
see. It is made from carbon and other materials
and eventually decomposes to become CO2. This
is a catabolic (breaking down) process. During
decomposition, the presence of SOM in soil has
beneficial effects for the soil food-web, the buffering
of soil temperatures and in reducing evaporation.
However, SOM is very short-lived (days to months).
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B- 23
- but not what’s needed to remove CO2 from the
atmosphere and lock it away for long periods.
Humus, on the other hand, is a high
molecular weight carbon polymer, formed by
soil microbes within soil aggregates, from sugars
channeled to soil via the hyphae of mycorrhizal
fungi living in association with actively growing
green plants. The formation of humus is an anabolic
(building up) process. Humus is an organo-mineral
complex requiring carbon, nitrogen, phosphorus,
sulphur and several catalysts, including iron and
aluminum. The carbon derives directly from
photosynthesis, the nitrogen is fixed by a group
of free-living nitrogen fixing bacteria called
‘associative diazotrophs’, while the phosphorus
is solubilized by bacteria from either calcium
phosphate, iron phosphate or aluminum phosphate
(depending on soil mineralogy and pH).
The chemical reactions involved in
making humus occur inside soil aggregates. The
transformations require microbial activity and the
microbes require energy - which is produced by
the green plants. That’s why humus cannot form
to any significant extent when there are no green
plants. Once formed, humus is an inseparable
part of the soil matrix and can be very long-lived
(as in hundreds of years). Hence it fulfils the
requirements for safely removing excess CO2 from
the atmosphere and storing it in soil. Humus is
called non-labile or resistant carbon. You cannot see
humus - you can only see what it does.
The main blockage to humus formation in
chemical ag is the use of synthetic fertilizers (N and
P) which inhibit carbon flow to soil. Even though
green plants are often present at high densities in
cash crops, they are not forming relationships with
mycorrhizal fungi and associative diazotrophs and
hence not building soil. This is a huge waste of
photosynthetic capacity! Simple changes to fertilizer
management alone could improve soil carbon
content (and farmers’ bottom lines). Farmers are
being encouraged to use products they do not need
by companies interested only in profit.