How carbon creates soils

November 29, 2021

For several decades Australian soil ecologist Dr. Christine 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 is an edited extract of an interview by Tracy Frisch that first appeared in ACRES U.S.A. magazine, March 2015.

There's a widespread belief that the formation of soil is an exceedingly slow process. Yet you describe the formation of topsoil as being breathtakingly rapid?

Most of the ingredients for new topsoil come from the atmosphere — carbon, hydrogen, oxygen and nitrogen.

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?

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. 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.

Liquid Carbon

Your term “liquid carbon” is such a brilliant phrase. What do you mean by it?

Liquid carbon is basically dissolved sugar. 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. The flow of liquid carbon to soil is the primary pathway by which new topsoil is formed.

All of which revolves around the concept of a plant-microbial bridge?

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.

We inadvertently blow the microbial bridge in conventional farming with high rates of synthetic fertilisers or with fungicides or other biocides.

Are you observing an increased awareness of the significance of biological processes?
There is a lot more energy generated through biological processes than through the burning of fossil fuels. 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.

We breathe out more CO2 than we breathe in, because as we utilise the energy we obtain from the assimilation of food, our cells release CO2. 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.

Mycorrhizal Fungi

You frequently mention mycorrhizal fungi in your work. What makes them so special?

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. Mycorrhizal fungi also transport a wide variety of other nutrients, including nitrogen, sulphur, potassium, calcium, magnesium and iron, and can extend quite a distance from plant roots.

They form networks between plants and colonies of soil bacteria. Mycorrhizal fungi are both the highway and the internet of the soil.

Rapid plant growth

I've learned from you that plants colonised by mycorrhizal fungi can grow much more robustly?

Yes, a mycorrhizal plant photosynthesises much faster than a non-mycorrhizal plant of the same species growing right next to it. If a plant photosynthesises 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.

Do 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.

Chemicals break Mycorrhiza

We always hear the story about fields where the soil is so exhausted that we have to add a lot of nutrients or we can't grow a thing.

The problem is that we interrupt carbon flow with the way we farm. If plants can obtain nitrogen or phosphorus easily, they will stop pumping carbon into the soil to support their microbial partners. 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. More efficient water use is going to be absolutely critical to the survival of our species.

Explaining aggregation

How can we tell if a soil has good aggregation?

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.

What processes are going on inside a soil aggregate?

Aggregates are fuelled by liquid carbon. Most aggregates are connected to plant 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. You'll rarely see a nitrogen deficient plant in a healthy, natural ecosystem.

Nitrogen forming bacteria

What should we know about free-living nitrogen fixing bacteria?

There are thousands of different types of bacteria and archaea that can fix nitrogen.

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 channelled to soil by plant roots. These organic forms of nitrogen cannot be leached or volatilised.

Synthetic Nitrogen

How dependent is the world on the application of synthetic nitrogen?

Farmers around the world collectively spend about $100 billion per year on nitrogen fertiliser. But 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 fertiliser. 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.

Diversity and creating soil

I want your recipe for transforming terracotta tile into chocolate cake — that is, turning hard, compacted soil into loose, fragrant soil teeming with life.

Soil becomes like a terra-cotta tile when aggregates break down. The first rule for turning this around is to keep the soil covered, preferably with living plants, all year round. Bare soil will be significantly hotter and lose more moisture than covered soil. Aggregation is absolutely vital for moisture infiltration and retention.

Point two is to maximise diversity in both cover crops and cash crops. Diversity above ground will correlate with diversity below ground. There are countless living things in soil.

Many farmers plant seeds treated with fungicide — they're actually preventing the plant from forming the beneficial associations that it needs in order to protect itself and inhibiting the soil fungi that are essential to crop nutrition and soil building.

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?

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. Cancer is also the number one killer in dogs. Isn't that telling us something about toxins in the food chain?

Cancer is not a transmissible disease. It's simply the inability of our bodies to prevent abnormal cells from replicating. The big breakthrough in cancer prevention will be in changing the way we produce our food.

Weeds and cover crops

You've talked about the pressure on farmers to have tidy farms and uniformity in their fields?

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.

One of the exciting things about the multi-species cover crop revolution that';s underway is that the greater the variety of plant types you use, the more niches you fill and the less opportunities there are for weeds.

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 realise that having all those different plants together is really beneficial. There is increasing worldwide recognition of the fact that multi-species cover crops improve soil-water relationships.

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. Lack of aggregation also renders the soil more prone to wind and water erosion.

Soil in transition

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?

If the soil is dysfunctional, chances are the wheels will fall off when fertilisers 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. Include some clovers or peas with your wheat, or vetch with your corn — just on one part of the field. This reduces the risk. Another option is to plant a multi-species cover crop on part of the land that would normally be devoted to a cash crop.

What about fertility?

It's important to cut back on chemical fertilisers slowly. At the same time as reducing fertiliser 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.

The longest-running field experiment in North America that found that high nitrogen depletes soil carbon?

The Morrow Plots are the oldest continuously cropped experimental fields in the United States. They discovered that the fields that had received the highest applications of nitrogen fertiliser had ended up with less soil carbon — and ironically less nitrogen — than the other fields.

If carbon is decomposing, then the soil will also be losing nitrogen. They decompose together.
Dr. David Johnson, based in Las Cruces, south of Albuquerque, 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. When you scoop up the soil, it has that lovely composty, mushroomy sort of smell that indicates good fungal levels.

Australian soils pre-colonisation

You've written about how lush and green Australia's landscape was at the time of European settlement in the early 1800s. How do your readers react?

They have a particularly hard time believing that the southern and southwestern parts of Australia supported green plants during our hot, dry summers.

In summertime when it was over 100 degrees (F) and without rain for months on end, George Augustus Robinson noted green grass and carpets of wildflowers everywhere he looked.

Sadly, by the late 1800s there were many millions of sheep in Australia, grazing the grasslands down to bare earth in the dry periods. When it rained, the unprotected soil washed away. We've lost around 2 to 3 feet of topsoil across the whole country.

Australian soil today

I read that in Australia, wheat production results in the loss of 7 kilograms of soil for every kilogram of wheat harvested. Is it still that bad?

Yes, probably worse. I have documented evidence of 20 tons of soil per hectare per year being lost through wind erosion. The average wheat yield in Australia is very low, around 1 ton per hectare. We lose massive amounts of soil to achieve it. The current situation is not sustainable.

How much of Australia's farmland would have to increase soil carbon to offset your country's carbon emissions?

It would require only half a percent increase in soil carbon on 2 percent of our agricultural land to sequester all Australia's CO2 emissions.

Agriculture is the major land use across the globe. According to the FAO there are around 1.5 billion hectares of cropland and another 3.5 billion hectares of grazing land. Currently much of that land is losing carbon.

The focus needs to be on transforming every farm that's currently a net carbon source into a net carbon sink. Activating the liquid carbon pathway requires that photosynthetic capacity be optimised.

Will adding compost help turn things around?

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.

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. The use of natural plant or seaweed extracts as biostimulants is a relatively new but rapidly expanding area of R&D and farmer-adoption worldwide.

These products stimulate soil biota and enhance plant root function. There can also be rapid improvements in soil structure.

Did you study soils because you loved to grow things?

In a roundabout way I became interested in the linkages between soil health, plant growth and animal production.

I undertook a Ph.D. in soil biochemistry to better understand how plants communicate with soil microbial communities. There haven't really been any light-bulb moments; it has been an ongoing process of discovery, finding the miraculous in the common.

 

This is an edited extract of an interview by Tracy Frisch that first appeared in ACRES U.S.A. magazine, Vol.45, No.3 in March 2015. Reprinted with kind permission.

ACRES is a highly regarded authority on large scale organic and sustainable farming: http://www.acresusa.com


For more information about Dr. Christine Jones visit:
http://www.amazingcarbon.com/