Dr. Christine Jones was interviewed in the March, 2015 issue of AcresUSA.
This article does a great job of explaining how carbon sequestration, the secretion of sugars into the soil by plant roots, is the absolute best method of creating wonderful, nutrient dense topsoil.
Here is the interview. Enjoy!
To the pressing worldwide challenge of restoring soil carbon and rebuilding topsoil, the Australian soil ecologist Dr. Christine Jones offers an accessible, revolutionary perspective for improving landscape health and farm productivity.
For several decades Jones has helped innovative farmers and ranchers implement regenerative agricultural systems that provide remarkable benefits for biodiversity, carbon sequestration, nutrient cycling, water management and productivity.
The following article is reprinted from the March, 2015 edition, volume 45, #3 of AcresUSA Magazine
Dr. Christine Jones, Interviewed by Tracy Frisch
ACRES U.S.A. You’ve written that the most meaningful indicator
for the health of the land and the long-term wealth of a nation is
whether soil is being formed or lost. Yet there’s a widespread
belief, actually dogma, that the formation of soil is an exceedingly
slow process. Even some organic researchers accept that idea.
describe the formation of topsoil as being breathtakingly rapid.
DR. CHRISTINE JONES. People have confused the weathering of rock,
which is a very, very slow process, with the building of topsoil,
which is altogether different. Most of the ingredients for new
topsoil come from the atmosphere — carbon, hydrogen, oxygen and
ACRES U.S.A. Why have many soil scientists denied the phenomenon
of rapid soil-building?
JONES. Because they do their research in places where it’s not
happening, where the carbon is running down and the soils are
deteriorating. We need to measure carbon on farms where
soil-building is occurring and see what the farmers and ranchers are
make that happen.
The process of fixing carbon in the soil seems to be
the crux of your work. You describe
a cycle with carbon in three
phases: as a gas, a liquid and a solid.
JONES. The issue we’re facing is that too much of the carbon that
was once in a solid phase in the soil has become a gas. That could
be dangerous for the human species. Climate change is just one
aspect. Food security, the nutrient density of food and the
water-holding capacity of the soil are also very potent reasons for
keeping carbon in a solid phase in the soil.
Your term “liquid carbon” is such a brilliant phrase.
It has really helped me conceptualize the carbon cycle. What do you
mean by it?
Liquid carbon is basically dissolved sugar. Sugars are
formed in plant chloroplasts during photosynthesis. Some of the
sugars are used for growth and some are exuded into soil by plant
roots to support the microbes involved in nutrient acquisition.
ACRES U.S.A. I remember bringing up the idea of leaky roots in a conversation with you and you laughed.
JONES. At first people thought “leaky” roots were defective.
Exuding carbon into the soil seemed such a silly thing for plants to
do! Then it became recognized that some of the exudates were
phenolic compounds with allelopathic effects, important in plant
defense. Of course we now know that plant roots exude a vast array
of chemical substances, all based on carbon, to signal to microbes
and to other plants. But perhaps the most significant finding, at
least from a human perspective, is that
the flow of liquid carbon to
soil is the primary pathway by which new topsoil is formed.
ACRES U.S.A. All of which revolves around the concept of a
JONES. In order for carbon to “flow” to soil, there has to be a
partnership between plant roots and the soil microbes that will
receive that carbon. Somewhere between 85 to 90 percent of the
nutrients plants require for healthy growth are acquired via carbon
exchange, that is, where plant root exudates provide energy to
microbes in order to obtain minerals and trace elements otherwise
unavailable. We inadvertently blow the microbial bridge in
conventional farming with high rates of synthetic fertilizers or
with fungicides or other biocides.
ACRES U.S.A. Are you observing an increased awareness of the
significance of biological processes?
JONES. There is a lot more energy generated through biological
processes than through the burning of fossil fuels. Most life-forms
obtain their energy either directly or indirectly from the sun, via
the process of photosynthesis. Plants are what we call autotrophs.
That is, they feed themselves by combining light energy with CO2 to
produce biochemical energy. As heterotrophs, we obtain energy by
eating plants or eating animals that ate plants. In effect, we’re
running on light energy too. Even microbes in a compost heap are
obtaining energy by breaking down organic materials originating from
the process of photosynthesis.
ACRES U.S.A. You distinguish between organic matter formed by the
decomposition of manure, crop residues or other carbonaceous
materials — and humus — which is generated via a building-up
process. I think a lot of times that is misunderstood.
JONES. It’s a really important distinction, but it’s often overlooked. In order to obtain the energy that is contained in cellulose, lignin, starches, oils, waxes or other compounds formed by plants, microbes have to break this material down — the same as we do when we digest starches or proteins or anything else of plant or animal origin. We breathe out more CO2 than we breathe in, because as we utilize the energy we obtain from the assimilation of food, our cells release CO2.
The decomposers in the soil are doing exactly the same thing —
breaking down organic materials and releasing CO2. These processes
are catabolic. Conversely, the formation of humus is an anabolic
process, that is, a building-up process. Rather than sugar being the
end point, sugar is the start point. Soil microbes use sugars to
create complex, stable forms of carbon, including humus.
ACRES U.S.A. How would you define humus?
JONES. Humus is an organo-mineral complex comprising around 60
percent carbon, between 6 and 8 percent nitrogen, plus phosphorus
and sulfur. Humic molecules are linked to iron and aluminum and many
other soil minerals, forming an intrinsic part of the soil matrix.
Humus cannot be “extracted” from soil any more than wood can be
“extracted” from a tree.
ACRES U.S.A. You frequently mention mycorrhizal fungi in your
work. What makes them so special?
JONES. Much of the initial research into mycorrhizal fungi was related to the uptake of phosphorus. Phosphorus is a highly reactive element. As soon as there’s any free phosphorus floating around in the soil, including whatever we may add as fertilizer, it becomes fixed. In other words, it forms a chemical bond with another element like iron or aluminum or calcium, making it unavailable to plants. But certain bacteria produce an enzyme called phosphatase that can break that bond and release the phosphorus.
Once released, the phosphorus still has to be transported back to the plant, which is where mycorrhizal fungi come in. As our analytical techniques have become more sophisticated, we’ve realized that mycorrhizal fungi also transport a wide variety of other nutrients, including nitrogen, sulfur, potassium, calcium, magnesium, iron and essential trace elements such as zinc, boron, manganese and copper. In dry times they supply water.
Mycorrhizal fungi can extend quite a distance from plant roots.
They form networks between plants and colonies of soil bacteria.
Plants can communicate with each other via messages sent through
these networks. Mycorrhizal fungi are both the highway and the
Internet of the soil.
ACRES U.S.A. How can something so important be overlooked?
JONES. Much of the agricultural research undertaken in pots in
glass houses is fundamentally flawed. Soil is homogenized to remove
background noise, that is, to make the soil in all the pots similar
at the outset. The blending process breaks up the hyphae of
mycorrhizal fungi. In some trials the soil is also sterilized to
eliminate any microbial activity that could interfere with the
treatment being assessed. And often the soil has been stored for a
long time prior to the experiments, which means most of the soil
organisms have died. In such an environment, plants are likely to
respond to applied fertilizer, as they have no other means to obtain
nutrients. Similarly with field trials, if the soil has been
cultivated or bare fallowed, mycorrhizal fungi will not be there in
sufficient quantities for effective carbon flow and nutrient
acquisition. In healthy, biologically active soils, we do not see a
response to synthetic nitrogen or phosphorus fertilizers. If
anything, the use of these is counterproductive.
ACRES U.S.A. I’ve learned from you that
plants colonized by
mycorrhizal fungi can grow much more robustly even though they’re
giving away as much as half of the sugars that they make in
photosynthesis through their roots.
JONES. That’s correct.
ACRES U.S.A. So we have this system characterized by abundance
and generosity, and that’s really different from the way we are used
to thinking about growing crops.
JONES. The point that’s often missed is that
a mycorrhizal plant
photosynthesizes much faster than a non-mycorrhizal plant of the
same species growing right next to it. The plant is able to give
half its energy away and still grow stronger because of the
symbiotic relationship with the fungus. It doesn’t cost the plant
anything to photosynthesize faster. It’s just using sunlight more
efficiently. Remember, plants are autotrophic.
ACRES U.S.A. And sunlight is free.
JONES. CO2 is free too.
If a plant photosynthesizes faster it’s
going to have higher sugar content and a higher Brix level. Once
Brix gets over 12, the plant is largely resistant to insects and
pathogens. High-Brix plants have formed relationships with soil
microbes able to supply trace elements and other nutrients that the
plant needs for self-defense, for its immune system. When plants are
able to produce high levels of plant-protection compounds, the
insects go elsewhere.
ACRES U.S.A. We tend to think that minerals in the soil are
scarce because most of them are not in a form available to plants.
A soil test will only tell you what is available to plants
by passive uptake. The other 97 percent of minerals — made available
by microbes — will not show up on a standard test.
By looking after
the microbes in the soil we can increase the availability of a huge
variety of minerals and trace elements — most of which are not even
ACRES U.S.A. We always hear the story about fields that were
continuously cropped or hayed for 30 years where the soil is so
exhausted that we have to add a lot of nutrients or we can’t grow a
JONES. The problem is that we interrupt carbon flow with the way we farm. Cultivating the soil and using chemical fertilizer and pesticides break up the mycorrhizal networks. If plants can obtain nitrogen or phosphorus easily, they will stop pumping carbon into the soil to support their microbial partners.
It’s taken a while for people to realize that plant root exudates are not only important for nutrient exchange, but also essential for the maintenance of topsoil. If carbon is not flowing to soil via the liquid carbon pathway, soil deteriorates. Carbon is needed for soil structure and water holding capacity as well as for feeding the microbes involved in nutrient acquisition.
When soil loses carbon, it becomes hard and compacted. The differences in infiltration and moisture retention between high and low carbon soils are dramatic. Planetary stocks of fresh water are declining alarmingly. More efficient water use is going to be absolutely critical to the survival of our species.
Making better use of water requires improved soil structure —
which in turn requires actively aggregating soils. If aggregates are
breaking down faster than they’re forming, the water-holding
capacity of soil can only deteriorate.
How can we tell if a soil has good aggregation?
JONES. Dig a hole and take a handful of soil. Squeeze it gently
and release. If the soil is well aggregated, it will look like a
handful of peas. If the soil remains in hard chunks that don’t break
easily into small lumps, then it isn’t well aggregated.
ACRES U.S.A. What processes are going on
inside of a soil
JONES. The aggregate is the fundamental unit of soil function. A great deal of biological activity takes place within aggregates. For the most part, this is fueled by liquid carbon. Most aggregates are connected to plant roots, often to very fine feeder roots, or to mycorrhizal networks unable to be detected with the naked eye.
Liquid carbon streams into the aggregates via these roots or fungal linkages, enabling the production of glues and gums that hold the soil particles together. If you gently lift a plant from healthy soil, you’ll find aggregates adhering to the roots. The moisture content is higher inside a soil aggregate than on the outside, and the partial pressure of oxygen is lower on the inside than on the outside. These important properties enable nitrogen-fixing bacteria to function.
When aggregates aren’t forming —
because of cultivating the soil
or using chemicals or having bare soil for six months or more with
no green plants — crops are not able to obtain sufficient nitrogen.
The tendency is then to add fertilizer nitrogen, exacerbating the
situation. The application of
large quantities of inorganic
nitrogen interrupts carbon flow to
soil, further reducing aggregation.
ACRES U.S.A. It sounds like a vicious cycle.
the more N applied, the more soil structure
deteriorates and ironically, the less N is available to plants.
You’ll rarely see a nitrogen deficient plant in a healthy natural
ecosystem. When I was driving home yesterday I noticed yellow,
nitrogen deficient pastures on many of the dairy farms I passed. But
in the area between the fence and the road, where no fertilizer had
been used, the grasses were a
lovely dark green.
ACRES U.S.A. We are familiar with Rhizobium bacteria and their
relationship with legumes. What should we know about free-living
nitrogen fixing bacteria?
JONES. From an agricultural perspective the most important of the
freeliving nitrogen-fixing bacteria are associative diazotrophs —
so-called because the atmospheric nitrogen that they fix occurs as di-nitrogen (N2) and associative because, like mycorrhizal
fungi, they require the presence of a living plant for their carbon.
These bacteria live in close proximity to plant roots or are linked
to plant roots via the mycorrhizal highway.
ACRES U.S.A. Isn’t our knowledge of these organisms pretty
JONES. The reason we know so little about associative diazotrophs is that most cannot be cultured in the lab. This applies to most species of mycorrhizal fungi as well. As bio-molecular methods for detecting microbes in the soil become more sophisticated, we’re realizing there is a lot more life — and a lot more species — than we thought. It has become obvious that there are thousands of different types of bacteria and archaea that can fix nitrogen.
The Haber-Bosch process, by which we manufacture nitrogen
fertilizer, is a catalytic reaction requiring enormous amounts of
energy. Yet microscopic bacteria in the rhizosphere or within
plant-associated aggregates can fix nitrogen simply using light
energy from the sun, transformed to biochemical energy during
photosynthesis and channeled to soil by plant roots.
ACRES U.S.A. I’m a little confused because I understood that
there is a difference between mineral nitrogen and organic nitrogen.
JONES. That’s correct. Nitrogen fixing bacteria produce ammonia, a form of inorganic nitrogen, inside soil aggregates and rhizosheaths. Rhizosheaths are protective cylinders that form around plant roots. They’re basically a bunch of soil particles held together by plant root exudates. You can easily strip them off with your fingers.
Within these biologically active environments the ammonia is rapidly converted into an amino acid or incorporated into a humic polymer. These organic forms of nitrogen cannot be leached or volatilized. Amino acids can be transferred into plant roots by mycorrhizal fungi and joined together by the plant to form a complete protein.
On the other hand, inorganic nitrogen applied as fertilizer often ends up in plants as nitrate or nitrite, which can result in incomplete or “funny” protein. This becomes a problem in cattle if it turns up as high levels of blood urea nitrogen (BUN) or milk urea nitrogen (MUN).
Nitrates cause a range of metabolic disorders including
infertility, mastitis, laminitis and liver dysfunction. There is
also a strong link between nitrate and cancer. In some places in the
United States it is not safe to drink the water due to excessive
nitrate levels. Milk can also have nitrate levels above the safe
drinking standard, but people happily consume it, not realizing it’s
ACRES U.S.A. These are great points. How dependent is the world
on the application of synthetic nitrogen?
JONES. Farmers around the world collectively spend about $100 billion per year on nitrogen fertilizer. I’m greatly inspired by the multi-species over crop revolution in the United States. Leading-edge farmers like Gabe Brown, Dave Brandt and Gail Fuller are showing it’s possible to maintain or even improve crop yields while winding back on fertilizer. These farmers are light years ahead of the science.
They’re building soil, improving the infiltration of water,
increasing water holding capacity and getting fantastic yields. They
have fewer insects and less disease. The carbon and water cycles are
fairly humming on their farms.
ACRES U.S.A. I want to get your recipe for transforming
terra-cotta tile into chocolate cake — that is, turning hard,
compacted soil into loose, fragrant soil teeming with life.
JONES. There isn’t a “recipe” as such for maintaining soil aggregates (the starting point for chocolate cake). It’s really just a set of guiding principles. Soil becomes like a terra-cotta tile when aggregates break down. Hard, compacted soil sheds water. The amount of effective rainfall is dramatically reduced. It’s also much harder for plant roots to grow in poorly aggregated soil.
The first rule for turning this around is to keep the soil covered, preferably with living plants, all year round. In environments where the soil freezes, it’s still important to maintain soil cover with mulch or a frost-killed cover crop or better still, a frost-hardy cover that will begin to grow again as soon as spring arrives.
Microbes will go into a dormant phase over winter and re-activate
at the same time as the plants. In regions with a hot, dry summer,
evaporation is enemy number one. Bare soil will be significantly
hotter and lose more moisture than covered soil. Aggregates will
break down unless the soil is alive. Aggregation is absolutely vital
for moisture infiltration and retention.
ACRES U.S.A. OK, so that’s one.
JONES. Point two is to maximize diversity in both cover crops and cash crops. Aim for a good mix of broadleaf plants and grass-type plants and include as many different functional groups as possible. Diversity above ground will correlate with diversity below ground.
Third, avoid or minimize the use of synthetic fertilizers, fungicides, insecticides and herbicides.
It’s a no-brainer that something designed to kill things is going to do just that. There are countless living things in soil that we don’t even have names for, let alone an understanding of their role in soil health. It’s nonsense to say biocides don’t damage soil! In Australia many farmers plant seeds treated with fungicide “just in case.” They’re actually preventing the plant from forming the beneficial associations that it needs in order to protect itself.
After a few weeks of crop growth, they will then apply a “preventative” fungicide, which also finds its way to the soil, inhibiting the soil fungi that are essential to crop nutrition and soil building. The irony is that plants are then unable to obtain the trace elements they need to fight fungal diseases. We see many examples of crops grown biologically that are rust-free, side-by-side with rust infected plants in neighboring fields where fungicides are being used.
There is an analogous situation with human health. Not that
long ago the cancer rate was around one in 100. Now we’re pretty
close to one in two people being diagnosed with cancer. At the
current rate of increase, it won’t be long before nearly every
person will contract cancer during their lifetimes. Cancer is also
the number one killer in dogs. Isn’t that telling us something about
toxins in the food chain? We’re not only killing everything in the
soil, we’re also killing ourselves — and our companion animals. Is
that what we want for our future?
ACRES U.S.A. Are you a cancer survivor?
JONES. Yes, I am, which is basically why I do what I do. But I
don’t say a lot about that because if you start your talk with
“we’re all going to die from cancer unless we change,” people tune
out. It’s too threatening. Most of us have lost loved ones through
ACRES U.S.A. You say it’s not just the toxins in our food that
are the problem, but the use of biocides — chemicals that kill
living organisms — which reduce the nutrient content of food. And
you attribute that nutrient reduction to the inhibition of the
JONES. Spot on.
If the plant-microbe bridge has been blown, it’s
not possible for us to obtain the trace elements our bodies need in
order to prevent
cancer — and a range of other metabolic disorders.
Cancer is not a transmissible disease. It’s simply the inability of
our bodies to prevent abnormal cells from replicating. To date, the
response to the cancer crisis has revolved around constructing more
oncology units, employing more oncologists and undertaking more
research. The big breakthrough in cancer prevention will be in
changing the way we produce our food.
ACRES U.S.A. We have plenty of evidence from meta-studies that
the nutrient content of produce grown organically tends to be higher
than produce grown chemically. We also have documentation of steep
declines in nutrient content in a number of foods over the last
JONES. Yes, we’re getting a double whammy. We’re ingesting
chemical residues, but not the trace elements and phytonutrients we
need for an effective immune response. Plants need trace elements,
like copper and zinc, to make these phytonutrients. But the trace
elements will not be available in the absence of an intact microbial
ACRES U.S.A. You’ve talked about the pressure on farmers to have
tidy farms and uniformity in their fields. It seems like one of the
problems you’re identifying is a faulty understanding of what it
means to farm well and to be a good farmer. What are some of the
qualities that farmers think they should have that get in the way of
building healthy soil?
JONES. I must admit that in the early ’90s, when I first started going onto farms that were using holistic planned grazing, I was a bit shocked to see the number of weeds popping up. These weeds would have been sprayed under the former management regime, but the ranchers were saying, “Don’t worry. We have to pass through this weedy stage. If we spray weeds, we create bare ground and the weed seed that’s there means the weeds simply come back.”
There’s a saying, “the more you spray weeds, the more weeds there will be to spray.” It’s oh so true! Continually reverting to bare ground creates more problems than it solves. Those ranchers knew some weeds had deep roots that bring up nutrients. Leaving them there meant better quality plants would eventually be able to grow in the improved soil and replace the weeds. That is exactly what happened. Over the last 60 years we’ve tried — and failed — to control weeds with chemicals.
One of the exciting things about the multi-species cover crop revolution that’s underway in the United States is that the greater the variety of plant types you use, the more niches you fill and the less opportunities there are for weeds. Cover-crop enthusiasts are experimenting with 60 or 70 different species in their mixes. I see the trend to polyculture as the most significant breakthrough in the history of modern agriculture. Even so, the first time you see a multi-species cover or a cash crop grown with companion plants, you might think, “Wow, that looks untidy” because we’re not used to it. It takes a little while to realize that having all those different plants together is really beneficial.
Somehow we have to change the image of what a healthy field looks like so that when people see bare ground or a monoculture, they recognize it’s lacking — and that this is not a good thing.
ACRES U.S.A. What sort of response are the cover crop pioneers
JONES. They’re seeing fantastic results. The trouble is they are not getting the accolades they deserve. This is slowly beginning to change. NRCS, in particular, are being exceptionally supportive of these leading edge farmers. Cover cropping is now generating a huge amount of interest.
Recently I visited Brendon Rockey, a young potato farmer in the
San Luis Valley of Colorado. Brendon has increased irrigation
efficiency 20 percent through the use of cover crops. There is
increasing worldwide recognition of the fact that multi-species
cover crops improve soil-water relationships.
ACRES U.S.A. Right, another aspect of that abundance.
JONES. If there is a bare fallow between crops — or bare ground between horticultural plantings such as grapes — soil aggregates break down. As a result, water cannot infiltrate as quickly. It remains closer to the surface and evaporates more readily. Lack of aggregation also renders the soil more prone to wind and water erosion.
We have this fear that if we grow companion plants or a cover
crop, they’re going to use up all the water and nutrients. We have
to realize that by supporting soil microbes,
a diversity of plants
actually improves nutrient acquisition and water retention.
ACRES U.S.A. In
the transition period from a chemically intensive
system where you don’t have a functioning plant-microbial bridge,
what are some kinds of practices that farmers can use?
JONES. Sometimes when farmers realize the importance of soil biology they immediately stop using fertilizers and chemicals. This is not necessarily a good thing. It takes time for soil microbial populations to re-establish. If the soil is dysfunctional, chances are the wheels will fall off when fertilizers are pulled. If there is a failure, farmers will revert back to what they know ... chemical agriculture.
You have to wind back slowly and accept that it’s going to take time to transition. The key to getting started is to experiment on small areas. It’s a matter of dipping a toe in the water. Include some clovers or peas with your wheat, or vetch with your corn — just on one part of the field.
This reduces the risk. When farmers see that they’ve gained rather than lost yield — and that the crop looks healthier — they will be inspired to try a larger area and a greater variety of companion plants next time. Another option is to plant a multi-species cover crop on part of the land that would normally be devoted to a cash crop.
You’re exceptionally lucky in the United States in that a lot of farmers are experimenting with cover crops now. Once the diversity ramps up, the ladybirds and lacewings and predatory wasps appear and the need for insecticides falls away. And after heavy rain, it’s obvious that water has infiltrated better in the parts of the field where the cover crops were.
Gradually the changes become an integral part of farming — an
exciting part, in fact. Experimentation and adaptation become the
norm, rather than conformity. Confidence builds, as ways to restore
healthy topsoil become firsthand knowledge.
ACRES U.S.A. What about fertility?
JONES. It’s important to cut back on chemical fertilizers slowly. If you’ve been using loads of synthetic nitrogen, then free-living nitrogen-fixing bacteria won’t be abundant in your soil. An easy way to transition is to reduce the amount of nitrogen applied by around 20 percent the first year, another 30 percent the next and then another 30 percent the year after.
At the same time as reducing fertilizer inputs it’s absolutely vital to support soil biology with the presence of a wide diversity of plants for as much of the year as possible.
Another way to gradually reduce fertilizer inputs is to use foliar fertilizers rather than drilling fertilizer under the seed. Foliar-applied trace minerals can also help during transition. These can be tank-mixed with biology-friendly products such as vermi-liquid, compost extract, fish hydrolysate, milk or seaweed extract.
Whichever path you choose to support soil biology, the overall
aim is for soil function to improve every year. The overuse of
synthetic fertilizers will have the opposite effect.
ACRES U.S.A. You mentioned the longest-running field experiment
in North America that found that high nitrogen depletes soil carbon?
JONES. The Morrow Plots are the oldest continuously cropped experimental fields in the United States. A team of University of Illinois researchers investigated how the fertilization regimes that were commenced in these plots in 1955 affected crop yields and soil carbon and organic nitrogen levels.
They discovered that the fields that had received the highest applications of nitrogen fertilizer had ended up with less soil carbon — and ironically less nitrogen — than the other fields.
The researchers concluded that adding nitrogen fertilizer
stimulated the kind of bacteria that break down the carbon in the
soil. The reason there is less nitrogen in the soil even though more
has been applied is that carbon and nitrogen are linked together in
organic matter. If carbon is decomposing, then the soil will also be
losing nitrogen. They decompose together.
ACRES U.S.A. That’s fascinating. Tell me about David Johnson and
what he is finding in his research at New Mexico State University.
JONES. Dr. David Johnson is based in Las Cruces, south of Albuquerque. He has discovered that the ratio of fungi to bacteria in the soil is a more important factor for plant production than the amount of available nitrogen or phosphorus.
Sadly, in most of our agricultural soils, we have far more bacteria than fungi. The good news is that farmers use multi-species cover crops, companion crops, pasture cropping and other polycultures — and the ranchers who manage their perennial grasses with high density short duration grazing accompanied by appropriate rest periods — are moving their soils toward fungal dominance.
When you scoop up the soil, it has that lovely composty,
mushroomy sort of smell that indicates good fungal levels.
Oftentimes agricultural soils have no smell or a smell that is a bit
sour. Fungi are important for soil carbon sequestration as well as
nutrient acquisition. The formation of humus, a complex polymer,
requires several catalysts, including fungal metabolites.
ACRES U.S.A. That is a really interesting insight. I would like
to get some perspective on soil degradation.
JONES. Many scientists have confused themselves — and the general public — by assuming soil carbon sequestration occurs as a result of the decomposition of organic matter such as crop residues. In so doing, they have overlooked the major pathway for the restoration of topsoil. Activating the liquid carbon pathway requires that photosynthetic capacity be optimized.
(Sections of this interview on 1. The cause of Australia's soil degradation, and 2. On offsetting carbon emissions, normally found here, have been left out for sake of brevity, but can be read in the full article)
ACRES U.S.A. When we talk about the consequences of the increased
extreme weather associated with climate change, like devastating
floods and droughts, all too often we neglect to consider how
better land management can reduce their impacts.
JONES. With weather events becoming more extreme our farming systems need to be more resilient. Again, this is where having carbon sequestered in soil to maintain aggregate stability and improve infiltration is vitally important.
If we look at flooding on the Mississippi, for example, we see that the mean maximum and mean minimum water levels from the early 1800s to the present show an increasing perturbation since the dust bowl era of the 1930s. That is, the highs are becoming higher — floods are more severe — and the lows are getting lower — the river doesn’t ‘run’ as much as it used to.
This boom-bust situation is due to inappropriate land management. If soil is in good condition, water infiltrates rapidly and is held in the soil profile. Some of this water is used for plant production and some will move downward through the soil to replenish the transmissive aquifers that feed springs and small streams, enabling year-round, moderated baseflow to river systems.
If groundcover is poor and soil water-holding capacity is low,
rapid run-off not only leads to flooding in lower landscape
positions, but also takes a lot of topsoil with it. These days it’s
not just soil, but a heap of chemicals too — which end up in the
Gulf of Mexico.
ACRES U.S.A. Causing the Dead Zone?
JONES. Yes. The consequences are enormous. And when the flood is
over, the river level drops because the transmissive aquifers
haven’t been recharged.
Is adding compost to the soil sufficient to turn
JONES. Compost is certainly a fantastic product, but compost alone is not enough. It will eventually decompose, releasing CO2. However, the application of compost to appropriately grazed pastures or polyculture crops can increase plant growth and photosynthetic rate, resulting in more liquid carbon flowing to soils.
Diverse microbial populations — particularly fungi — supported by the compost, can aid in humification, improving soil structure, water-holding capacity and nutrient availabilities.
On large agricultural holdings such as we have in many parts of Australia, it is not economically viable to spread compost. However, compost extract, which is simply the chemical signature of compost, can prove highly beneficial.Bio-stimulants.
The use of natural plant or seaweed extracts as bio-stimulants is a relatively new but rapidly expanding area of R&D and farmer-adoption worldwide. The advantage of bio stimulants is that they function at very low rates of application — milliliters per hectare — as opposed to a product such as compost which needs to be applied in tons per hectare.
These products stimulate soil biota and enhance plant root function. The proliferation of roots is quite obvious when you dig in the soil. There can also be rapid improvements in soil structure.
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