Turning dirt into soil

WORKING IN SUSTAINABLE food and agriculture means confronting some of the biggest wicked problems of our time: climate change, declining fresh water, a projected global population of nine billion people, and the planet's ability to supply their needs for food, fibre and energy. Solutions to any one raises problems in solving the others at the nexus of water, energy and food production.

For some time I have had a hunch that remedies lie in things that grow, that come from the soil: things of an agrarian nature. Can we harness the prolific and continuous energy from the sun, through nature's mechanism of photosynthesis, to meet our needs for food, fibre and energy? Can the planet support a healthy population half as big again? Biomass for green energy production, algae for oil, closed-loop agricultural systems for the production of nutritious food and fibre – these are the kind of things-that-grow scenarios with which I am preoccupied.

In early 2011 I participated in an extraordinary meeting of twenty of the world's leading soil and plant scientists. The scientists came to Sydney from North America, the United Kingdom, Europe and Australasia for the inaugural Soil Carbon Summit to deliberate the science of soil carbon sequestration and its potential in improving soil function, abating climate change, and girding water, food and energy security. What made this meeting unique was the calibre of the people in the room: six centuries of combined experience, the very top minds in soil science in the world. This esteemed group very quickly established consensus on the state of the science of soil, and concluded that soil carbon sequestration has the potential to secure the future of the world's soils.

This is the story of what emerged: the conclusions reached and the message of hope that it produced. We can solve these big wicked problems. This is the story of soil.

Most of us now know that too much carbon in the atmosphere is a bad thing, but few realise that the reverse is true in the case of soil: carbon in soil is a good thing. Carbon in soil is essential for life. The carbon in soil holds it together. Without carbon, soil is dirt that grows nothing. Carbon in soil powers the nutrient cycle, nutrients in dead organic matter turning back into a form that promotes the growth of food and fibre. The carbohydrates we eat in various forms every day depend on how the soil in which they are grown interacts with carbon and the plant. The other terrestrial foods in our diet also rely on soil carbon: without it, it is impossible to grow protein and fats – meat, plants or dairy.

Carbon in soil is a great indicator of the fertility and resilience of the soil. Soil that is high in carbon retains more water, is resistant to erosion and produces more food. Carbon in soil is unambiguously a good thing.

Unfortunately, low and declining carbon stocks in soils are a global phenomenon. Scientists are desperately concerned about soil degradation. The idea of 'peak soil' is emerging: that, if we continue on current trajectories, we may only have between sixty and a hundred years before we run out of functional soil. The recent flooding and erosion of Queensland's agricultural soils on a massive scale may have brought the peak a little closer.

This decline in soil carbon is occurring because agricultural practices in the developed world focus on high yield. 'Yield' is the language of the modern farmer. The green revolution gave birth to the industrial agricultural system that provides food and fibre. This is a highly sophisticated system of plant and animal breeding, with inputs in the form of synthetic fertilisers and pest management in various -icides, all designed to maximise yields. The goal of the green revolution was to produce more food to feed the hungry. It has been one of the great innovations of modern times. It has released people from subsistence farming to pursue fulfilling and productive urban lives.

It was not designed to conserve soil carbon. Over the decades the world's farmers have produced more and more food and fibre, while inadvertently mining soil carbon.


WE CAN, THOUGH, get the carbon out of the atmosphere into the soil where it is needed. As I learned at the Soil Carbon Summit, there is sufficient scientific knowledge to make a start. The summit marked a turning point when scientists were happy to say, 'the science can now predict soil carbon sequestration and stabilisation.' The mathematical models of soil carbon transformations are well enough developed. We know roughly what inputs will make a difference. We understand the interactions between the microbial communities in soils with soil carbon, and how this affects the movement of carbon between its various forms or pools within the soil. We also know – for different soil types, under various climatic conditions – a range of technologies and farming practices that increase soil carbon, while producing food and fibre. Australian farmers have led the world in developing a new range of innovative practices that appear to do this. The science is sufficiently developed to underpin a refocusing of agricultural practice to produce food and fibre that builds rather than mines soil carbon. This is a paradigm shift on the scale of the green revolution – finding solutions to wicked problems in things that grow.

Building carbon stocks in soil will future-proof food production. We cannot continue to mine soil carbon to produce food: when the soil carbon runs down, the productivity of the soil goes too. Restoration of soils by managing soil carbon is the key to future food security. This relies on enhancing natural processes; it can't happen just by throwing bricks of carbon into depleted soil.

A lot of other good things happen when we start to secure our soils by replenishing soil carbon stocks. The carbon that goes into the soil comes from the atmosphere. This is basic biology: photosynthesis. Plants take in carbon dioxide from the air, and release oxygen. The plant uses the carbon to grow, and if the conditions are right the carbon goes through the plant's root system and into the soil – this is the beginning of soil carbon accumulation. Creating the right conditions can be achieved by adjusting land-management practices. Some of these, such as minimising tillage or ploughing of the soil, manuring and composting, and growing deep-rooted pastures, are well established. Up to four-fifths of Australian cropping farms already practise minimum tillage; seed is 'direct drilled' into the soil without ploughing. Increasing numbers of graziers are switching to intensive 'cell-grazing' techniques, with high rotations of livestock through small paddocks. Pastures are grazed intensively and then the stock moved on, so that the top of the plant regenerates, leaving the root systems intact. Natural, biological fertilisation occurs through the manure. Some innovative farmers are adding 'poultry tractors' into this mix, bringing large mobile chook runs in to feed on the bugs associated with cow manure, and add nitrogenous chicken manure to the system.

Other land-management practices need calibration with the science. Australia leads the world in the development of innovative new farming systems that build soil carbon. Pasture cropping, planting crops into deep-rooted native perennials, is one such practice. Making and using compost and compost teas as alternatives to commercial fertilisers is increasing. Some Western Australian farmers have converted their cropping system to grazing, using deep-rooted shrubs as fodder that hold down the soil and sequester carbon to depth. Biochar will play a role in adding soil carbon to some systems, but it is not a silver bullet – rather a piece of silver shrapnel. Black carbon is one form of soil carbon; healthy soil requires many forms. Innovative, localised pyrolysis (heat-driven decomposition) techniques may be part of the mix of solutions to be developed as the new paradigm emerges.

Soils that contain high levels of carbon have better structure and retain more water, while soils low in carbon are more likely to erode as wind or water move across them. Soils have a critical role in triaging rainfall. Carbon-rich soils effectively partition rainfall into infiltration and runoff; carbon, together with weather and crops, determines this partitioning. The amount of water that runs over the surface and causes floods and erosion, as well as the amount that flows into the soil profile, is directly related to the soil carbon. This underground hydrology is important, as it contributes to the recharge of water into groundwater systems, and the storage of water in soil to make it available for plants to grow. Soils that are low in carbon don't have this sponge-like capacity, so they are less productive during dry periods. Farmers who are using practices that build soil carbon are already realising the drought-proofing benefits.


SOIL AIN'T JUST soil. There are many different types, reflecting the diverse geological and climatic environments that they have been built from across the millennia. Soils are made up of complex mixes, including carbon and minerals in various forms, sophisticated and diverse communities of living organisms. Australia has the widest and most comprehensive range of soil types. The diversity of our agriculture reflects the fickle climate and variety of soils, from the sandy soils of the west to the red-brown earths of the grain belt, the fertile alluvial black-soil flood plains and the iron-rich soil of the north-east. These are depleted in carbon. Australian soils under cultivation have lost at least half their soil carbon since the introduction of European agricultural methods.

Australian agriculture has been honed in these tough conditions. Replacing the carbon in our soils will require a range of different land-management practices and technologies. Our farmers are the most innovative, professional and competitive in the world: we have the capacity to make the necessary adjustments. Australia leads the world in soil science, and has done so for some time. We attract the best international talent, because of the diversity of soils, which need such attention. We are well positioned to lead the world in the new paradigm.

The science is ready, and we know what to do: there are five key measures. First, building soil carbon in soils must become a priority in the drive to increase food production to feed the growing world population. Second, public policy must recognise agricultural soil as a national asset, and protect and rebuild this vital resource. Third, farmers must be recognised as the stewards of the asset, and supported through policy measures in their role of managing the asset to rebuild soil carbon in addition to maximising yields of food and fibre. Building better connections between farmers and the science of soil carbon will play a critical role. Fourth, agricultural research and development must recalibrate to address yield maximisation within a framework of soil security, preservation and conservation. Fifth, and critically, we must continue the scientific endeavour to understand soils and soil carbon. Soil science has been dismally underfunded for decades, partly in lieu of water and landscape research. When I say the science is ready, it is really the starting point. For soils to be the solution, we must pursue scientific knowledge of soils relentlessly and not rest on our laurels.

Soil security deserves as much attention as climate change, if not more. To aim for soil security, by managing soil carbon stocks in the world's soils, is a roadmap to helping solve not only climate change but also food, water and energy security. While the world has been dumbstruck in response to climate change, we have failed to look down and see that the solution may lie beneath our feet.


A FEW DAYS after the summit, my mind still buzzing, I visited a friend whose husband is a keen plant collector. Their garden overflows with an unrivalled botanical collection. As I stepped out of the car I saw a small sign hanging to the branch of a rose bush: 'To forget how to dig the earth and tend the soil is to forget ourselves – Gandhi.'

It was as though those words were placed there as an affirmation of what I had learned. They encapsulate the brink on which we stand, a moment in time where we can refocus our intent on things that grow, with a new respect for the soil that gives them life. The goal is to secure our soils; the way to achieve it is by managing and increasing soil carbon.

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