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How carbon creates soils
For several decades Australian soil ecologist Dr. Christine Jones (CJ) 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 (TF) that first appeared in ACRES U.S.A. magazine, March 2015.
(TF) 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?
(CJ) 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.
(TF) You describe a cycle with carbon in three phases: as a gas, a liquid and a solid?
(CJ) 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.
(TF) All of which revolves around the concept of a plant-microbial bridge?
(CJ) 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.
(TF) How would you define humus?
(CJ) Humus is an organo-mineral complex comprising around 60 percent carbon, between 6 and 8 percent nitrogen, plus phosphorus and sulphur. Humic molecules are linked to iron and aluminium 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.
(TF) You frequently mention mycorrhizal fungi in your work. What makes them so special?
(CJ) 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.
(TF) I’ve learned from you that plants colonised by mycorrhizal fungi can grow much more robustly?
(CJ) 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.
(TF) 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.
(CJ) 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.
(TF) How dependent is the world on the application of synthetic nitrogen?
(CJ) 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.
(TF) You’ve talked about the pressure on farmers to have tidy farms and uniformity in their fields?
(CJ) 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.
(TF) What about fertility?
(CJ) 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.
(TF) 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?
(CJ) They have a particularly hard time believing that the southern and south-western 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 2-3 feet of topsoil across the whole country.
(TF) I read that in Australia, wheat production results in the loss of 7kg of soil for every kilogram of wheat harvested. Is it still that bad?
(CJ) Yes, probably worse. I have documented evidence of 20 tonnes of soil per hectare per year being lost through wind erosion. The average wheat yield in Australia is very low, around 1 tonne per hectare. We lose massive amounts of soil to achieve it. The current situation is not sustainable.
(TF) How much of Australia’s farmland would have to increase soil carbon to offset your country’s carbon emissions?
(CJ) 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.
(TF) Will adding compost help turn things around?
(CJ) 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 poly-culture crops can increase plant growth and photosynthetic rate, resulting in more liquid carbon flowing to soils.
Editor’s note: 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.