Farmers have a golden solution to global warming largely missed by climate change pundits, right beneath their feet. The innovative Australian Soil Carbon Accreditation Scheme is showing how incentive payments can be received by landholders for measurable increases in soil carbon that soaks up CO2 from the atmosphere. Financial incentives could help fund soil restoration efforts, which in turn bring the bonus of greater productivity, drought resilience and even rain. The action is deep underground.

 

Australian soil scientist Dr Christine Jones is frustrated that the world hasn’t fully cottoned on to the important role of healthy crop roots and soils to draw down massive amounts of carbon, buffer drought and re-supply essential nutrients which have been drained from our landscape and farm produce by traditional agricultural practices.

Her 10-year crusade to raise the profile of soil carbon processes and what she calls the microbial ‘carbon highway’ led to the foundation of the organization Amazing Carbon and then to the development and leadership of the Australian Soil Carbon Accreditation Scheme (ASCAS).

ASCAS is a vehicle to demonstrate through farm trials that with biologically based protocols involving perennial (long-lived) deep-rooted pastures and annual crops, measured increases in vital soil carbon can be achieved quickly and rewarded with incentive payments for the CO 2 sequestered. The scheme is the first of its kind in the Southern Hemisphere, making Australia an early leader in the recognition of soils as a verifiable carbon sink.

The ASCAS project is also collecting much-needed hard data on soil carbon accumulation rates across various properties and soil types in the Northern Agricultural Region (NAR) of Western Australia and central Queensland, two of the areas hardest hit by climate change.

After the oceans, the soil is the earth’s largest carbon sink – but plants are the facilitators. Through photosynthesis plants convert CO 2 to sugars to power growth, releasing oxygen into the atmosphere. The activities of symbiotic bacteria and fungi, associated with roots and fed by the sugars, enable the exuded carbon to be combined with soil minerals and made into stable humus1 which locks the carbon away.

The fundamental processes which produce humified soil carbon are part of the microbial bridge – the focus of Dr Jones’ interest – and the key to the formation and maintenance of healthy topsoils with high moisture-holding capacity, which largely determines plant and crop productivity.

‘This can’t happen where farm chemicals kill the essential soil microbes,’ says Dr. Jones. ‘When chemical use is added to intensive cultivation, which exposes and oxidizes the humus already in the soil, it is easy to see why soil has become a huge net source rather than a net “sink” for atmospheric CO2 under current farming practices.’

Alongside this, the removal of groundcover interrupts the important water and climate cycles facilitated by plants. Photosynthesis is a cooling process. Lack of green cover on the land greatly increases heat absorption, causing a dramatic increase in evaporation. Water vapor is a greenhouse gas of greater significance for global warming than CO 2. Lower rainfall can also result from groundcover loss.

Under conventional cropping practices, soil carbon in Australia has declined to one-half to one-third of original levels. CSIRO research has found that the rate of carbon sequestration resulting from good continuous pastures is enough to maintain or increase soil carbon levels, but all other crops/pasture rotations cause a decline of surface soil carbon.

Dr. Jones claims that conventional approaches to modeling soil carbon, while useful for describing soil carbon loss, are inadequate for determining soil carbon gain. Soil carbon models such as Roth C do not take into account the humification of root exudates or contributions from mycorrhizal fungi. ‘Sequestration rates under regenerative agricultural regimes may be quite a bit higher than estimated by current models,’ she says.

The scheme is the first of its kind in the Southern Hemisphere, making Australia an early leader in the recognition of soils as a verifiable carbon sink.

Tim Wiley, Development Officer with Western Australia’s Department of Agriculture and Food, was quick to realize the great potential of soil carbon increases with perennials. Wiley has been supporting the ASCAS trials in the NAR of WA. ‘The trend is clear – perennial pastures sequester 5 to 10 tonnes of CO 2 per hectare annually.’ He says with changes to farming practice, landholders in the northern agricultural areas of WA could sequester these amounts of CO 2 over two million hectares of poor sandy soil.

‘If all WA’s agricultural soils were sequestering carbon, we would soak up WA’s current emissions. This would have the potential to significantly decrease Australia’s net emissions and meet our Kyoto obligations.’

Add in the rest of Australia’s agricultural land area – and the world’s – and the impact on global CO2 levels is evident. Wiley pointed to current cost and data limitations to quantitative measurements of soil carbon. ‘We don’t know enough about carbon under different farming systems,’ he said. ‘We have data from farmer sampling before and after perennials were planted and over-the-fence comparisons, but it is not rigorous enough.

‘To trade carbon we need a working model such as Roth C for estimating changes in carbon. The model results would be verified by occasional soil sampling of farmers’ paddocks. Roth C needs to be validated with data from long-term trials in the regions that accurately measure carbon.’ That’s where the ASCAS trials are filling in the picture.

Up at Lancelin, about 140 km north of Perth, things have been tough during the last 10 years of below-average rainfall. But cattle farmer Bob Wilson hasn’t been too fazed; since changing his farming system over the past 20 years from traditional annual pastures to the fast-growing fodder shrub, tagasaste, and subtropical perennial (permanent) grasses, his farm has ridden out the dry far better than most, producing good returns.

As a member of the Evergreen Farming Group, he hasn’t been surprised by the exciting results of the ASCAS trials. His band of farmers advocates growing hardier perennial plants which improve the soil and help stave off salinity. Two decades ago the view to the future of farming opened up for Wilson and his colleagues, and it looked much greener.

Unlike some of the other farmers involved in the ASCAS trials, Wilson has been growing perennials for some time. Using the scheme’s protocols he has been able to measure soil carbon on his land and quantify to some extent how it can improve yields, increase water and nutrient retention for greater farm vigour, and now, potentially bring useful credit income for sequestering carbon dioxide.

He now has half his 2000 ha under tagasaste in wide rows with annual pastures in between. ‘I changed my farming system because of concern for the environment, wind erosion, and our need for an extended grazing season. We have doubled our carrying capacity.’

But he points out that while subtropical perennials provide an extended period of green feed, they grow slowly during winter and are susceptible to frosts. ‘We need annuals as well for winter feed. A mixture of pasture types is best, on a case by case basis,’ he says. When Tim Wiley dug soil pits in Bob Wilson’s paddocks, he found perennial grass roots at the bottom of a 2.5 m deep pit and tagasaste roots at the bottom of a 3 m pit. He calculated from the soil test and other results that the perennial grasses and tagasaste were sequestering 7 t/ha of CO2 per year more than traditional annual
pastures.

The group of 12 farmers involved in ASCAS ‘benchmarking’ in the Northern Agricultural Region of WA over the last year will later in 2008 be completing calculations to see how much carbon has been sequestered under their perennial pastures. Baseline soil carbon levels in five increments in the 110 cm soil profile were determined during August 2007 within Defined Sequestration Areas on their properties.

Results from the first 12 months of field trials in Queensland will also be known later this year. Dr. Jones says the initial findings have been exciting. ‘One of the broadacre cropping properties north-east of Clermont in Queensland that is participating in the ASCAS project has more than three times the amount of carbon in the farmed soil than there is under the surrounding native vegetation (149 tonnes of carbon/ha under native vegetation versus 516 tonnes of carbon/ha under the crop). As a result, the soil is far more productive. The wheat crop yielded 4 tonnes per hectare of grain with 13.5 percent protein this year – well above the district average.

‘This demonstrates that with the right kind of farming (in this case zero till with microbial stimulants in place of harsh fertilizers) we can dramatically improve soil health. I’m not saying we should replace native vegetation with farmed land – far from it. What I am saying is there is still hope for much of the land that we have inadvertently almost totally destroyed,’ she observes.

Under the Australian Soil Carbon Accreditation Scheme, participating farmers will receive Soil Carbon Incentive Payments (SCIPS) calculated at one-hundredth the 100-year rate ($25 per tonne CO 2 sequestered).

The incentive payments made to farmers are a private donation from Rhonda Willson, Executive Chairman, John While Springs (S) Pte Ltd and Director, Gilgai Australia.

Receipt of Soil Carbon Incentive Payments will be similar to being paid ‘on delivery’ for livestock or grain, with the bonus being that sequestered carbon remains in the soil, conferring multiple landscape health and productivity advantages.

Agricultural soils have short-, medium, and long-term potential to mitigate climate change by sequestering atmospheric carbon as beneficial humified organic matter. Results from overseas studies indicate that the carbon sequestration potential of appropriately managed farmlands can be higher than that of tropical forests. In countries such as Brazil, Colombia, Costa Rica, Mexico, and Cuba, the science of soil carbon is the subject of active research and development.

Dr. Jones says the rationale for the ASCAS trials was to demonstrate that significant quantities of soil carbon could be sequestered on Australia’s commercial properties, even under difficult environmental conditions, provided appropriate land management technologies were employed.

Apart from needing to be rapid, stable, and applicable to large areas, soil carbon sequestration as an effective climate mitigating tool must involve low-cost, easily implemented, innovative land management techniques that differ substantially from ‘business as usual. There also needs to be effective monitoring, evaluation, and verification, particularly when measures of carbon sequestered might be linked to a financial mechanism.

At present, an emissions trading scheme does not operate in Australia, although a national scheme is planned in line with the government’s recent ratification of the Kyoto accord. Rio Tinto Coal Australia is currently one of the organizations funding research into soil carbon and its potential for a future carbon trading scheme under ASCAS.

Recent good news is that Australian agricultural products company Incitec Pivot Ltd has also come on board as a supporter of the Queensland field trials. Of the estimated 3060 gigatonnes of carbon in the terrestrial biosphere, 82 percent is in soils.2 That’s over four times the amount of carbon stored in the world’s vegetation. Dr. Jones asks, ‘If only 18 percent is stored in vegetation, why all the emphasis on biomass, rather than soil, as a carbon sink?

‘The answer is that people – including most of our top scientists – simply don’t understand soil carbon sequestration or the role of the microbial bridge and have therefore overlooked it.

‘ASCAS was established so that farmers could receive incentive payments for increases in their soil carbon. We’re demonstrating the incredible rates at which carbon can be put into soil by roots in biologically based sustainable cropping and grazing systems,’ she says.

‘Effective soil carbon management is a key factor for productive farms, revitalized catchments, and a greener planet.

‘Incentive payments for regenerative land management would help to “cash flow” the multiple natural resource management and environmental benefits that accompany increased levels of carbon in soils.’

The capacity for appropriately managed soils to sequester atmospheric carbon is enormous. The world’s soils hold around three times as much carbon as the atmosphere and over four times as much carbon as the vegetation. Soil represents the largest carbon sink over which we have control.

When atmospheric carbon is sequestered in topsoil as organic carbon, it brings with it a wealth of environmental, productivity and quality of life benefits. An understanding of the ‘carbon cycle’ and the role of carbon in soils, is essential to our understanding of life on earth.

Building soil carbon requires green plants and soil microbes. ‘There are 4 steps to ‘turning air into soil’

i) Photosynthesis

ii) Resynthesis

iii) Exudation

iv) Humification

Photosynthesis is a two-step endothermic reaction (ie a cooling process) which takes place in the chloroplasts of green leaves. Incoming light energy (sunlight) is captured and stored as biochemical energy in the form of a simple sugar – glucose (C6H12O6), using carbon dioxide (CO2) from the air and water (H2O) from the soil. Oxygen is released to the atmosphere.

Photosynthesis requires 15 MJ of sunlight energy for every kilogram of glucose produced. If the same 15 MJ of incoming light energy makes contact with a bare surface, such as bare ground, it is reflected, absorbed or radiated – as heat, usually accompanied by moisture. The respective area of the earth’s surface covered by either actively growing crops and pastures, or bare ground, has a significant effect on global climate.

Resynthesis: Through a myriad of chemical reactions, the glucose formed during photosynthesis is resynthesised to a wide variety of carbon compounds, including carbohydrates, proteins, organic acids, waxes and oils. Carbon atoms can link together to form long chains, branched chains and rings, to which other elements, such as hydrogen and oxygen, can join.

The energy captured during photosynthesis and stored in carbon compounds serves as ‘fuel’ for life on earth. Carbohydrates such as cellulose provide energy for grazing animals, the starch in grains provides energy for livestock and people. The carbon stored in previous eras as ‘fossil fuels’ (hydrocarbons) such as coal, oil and gas provides energy for vehicles, machinery and industry.

 

 

Exudation: Around 30-40% of the carbon fixed by grass plants during photosynthesis is exuded into the soil to form a microbial bridge (to feed the microbes that enhance the availability of essential plant nutrients). In this way, actively growing crops and pastures provide ‘fuel’ for the soil engine.

Carbon compounds are essential to the creation of topsoil from the structureless, lifeless mineral soil produced by the weathering of rocks.

Organic carbon additions are governed by the volume of plant roots per unit of soil and their rate of growth. The more active green leaves there are, the more roots there are, the more carbon is added. It’s as simple as that (Figure 1). The breakdown of fibrous roots pruned into the soil through rest-rotation grazing is also an important source of carbon in soils.

Humification: Adding organic carbon to soil is one thing, keeping it there is another. Organic carbon moves between various ‘pools’ in the soil, some of which are short-lived while others may persist for thousands of years. Carbon additions need to be combined with land management practices that foster the conversion of relatively transient forms of organic carbon to more stable complexes within the soil.

In the humification process, soil microbes resynthesize and polymerize labile carbon (exuded from plant roots) into high molecular weight stable humic substances. Humus, a gel-like substance that forms an integral component of the soil matrix, is the best known of the stable organic fractions.

Humification cannot proceed unless there is a continuous supply of ‘fuel’ for soil microbes. If humification does not occur, the carbon exuded from plant roots (or added to soil as plant residues or manure) simply oxidizes and recycles back to the atmosphere as carbon dioxide.

Humic substances have significance beyond the relatively long-term sequestration of atmospheric carbon. They are extremely important in pH buffering, inactivation of pesticides and other pollutants, improved plant nutrition, and increased soil-water-holding capacity. By chelating salts, humic substances can also effectively ameliorate the symptoms of dryland salinity. Increasing the rate of humification has highly significant effects on the health and productivity of agricultural land.

Importance of soil fungi

Most perennial grasses are excellent hosts for mycorrhizal fungi, with up to 100 meters of microscopic fungi forming per gram of soil under healthy grassland. Glomalin is a glycoprotein (contains both protein and carbohydrate) produced by arbuscular mycorrhizal fungi living on plant roots. Glomalin can persist for several decades and may account for one-third of the stable organic carbon stored in agricultural soils.

Mycorrhizal fungi and glomalin production are inhibited by bare soil, intensive tillage, the application of phosphorus fertilizer, and the presence of plants from the Brassica family such as canola, which do not form mycorrhizal associations.

Maintaining soil structure

‘Aggregation’ is part of the humification and soil carbon building process and is essential for maintaining soil structure. Glues and gums from fungal hyphae in the rhizosphere enable the formation of peds or lumps (which can be seen with the naked eye, often attached to plant roots). The presence of these aggregates creates macropores (spaces between the aggregates) which markedly improve the infiltration of water. After rain less water sits on the soil surface and waterlogging is reduced. As structure continues to improve, smaller and smaller aggregates are formed, along with soil mesopores and micropores, dramatically improving soil function, aeration, levels of biological activity, and resilience.

Soil structure is not permanent. Aggregates made from microbial substances are continually breaking down and rebuilding. An ongoing supply of energy in the form of carbon from actively growing plant roots will maintain soil structure. If soils are left without green groundcover for long periods they can become compacted, blow or wash away.

Under conventional cropping or set-stocked annual pastures, the stimulatory exudates produced by short-lived species are negated by bare earth at other times of the year. The result is a decline in levels of soil carbon, soil structure, and soil function. Soil building requires green plants and soil cover for as much of the year as possible. In seasonal rainfall environments, a mix of perennial groundcover species enables response to rain at any time. In grazing enterprises, rest-rotation grazing is absolutely essential. For broadacre cropping, the presence of out-of-season groundcover ensures stability, long-term productivity, and soil building rather than soil destruction.

Any farming practice that improves soil structure is building soil carbon. Water, energy, life, nutrients, and profit will increase on-farm as soil organic carbon levels rise. The alternative is the evaporation of water, energy, life, nutrients, and profit if carbon is mismanaged and goes into the air.

Yearlong Green Farming (YGF) is any practice of turning bare soil into soil covered with green plants. YGF increases the quality, quantity, and perenniality of green groundcover in broadacre cropping, horticultural, forestry and grazing enterprises.

Many benefits of Pasture Cropping, for example, can be attributed to having perennial grasses and cereals together side by side in space and time. Ongoing carbon additions from the perennial grass component evolve into highly stable forms of soil carbon while the short-term, high sugar forms of carbon exuded by the cereal crop roots stimulate microbial activity.

As a bonus, regenerative farming practices such as Pasture Cropping result in the production of food much higher in vitamin and mineral content and lower in herbicide and pesticide residues than conventionally produced foods.

Rewarding farmers for Yearlong Green Farming practices that build new topsoil and raise levels of organic carbon would have a significant impact on the vitality and productivity of Australia’s rural industries. YGF would also reduce evaporation and heat radiation from bare soil surfaces, reduce the incidence of dryland salinity and counteract soil acidity.

Under regenerative regimes, soil carbon and soil life are restored, conferring multiple ecological and production benefits in terms of nutrient cycling, soil water storage, soil structural integrity, and disease suppression. Benefits extend well beyond the paddock gate. Improved soil and water quality are the ‘key’ to catchment health, while YGF represents the most potent mechanism available for mitigating climate change.

It’s about turning carbon loss into carbon gain.

Getting started in lifeless, compacted soils where the soil engine has shut down is the hard part. The longer we delay, the more difficult it will be to re-sequester soil carbon and re-balance the greenhouse equation.

Let’s begin with a topic that interests all farmers and one to which nearly all the other benefits of mycorrhizae are inherently linked: improving crop yields. Typically, mycorrhizae’s single most prominent contribution to a crop plant is improved access to and uptake of phosphorus (P).

All farmers are intensely familiar with the importance of this elemental nutrient to essential plant functions, which include energy transfer, photosynthesis, the transformation of carbohydrates, systemic nutrient mobilization, and genetic transfers. Given that often one of the most noticeable evidence of P deficiency in a crop is reduced yield (or in forage and pasture reduced quantity), it is no wonder that P is such a critical (and expensive) component in crop fertilizers.

Much of the naturally-occurring P in soils is found bound tightly with elements such as iron or aluminum in the form of recalcitrant compounds. Similarly, P inputs derived from fertilizers often react with ambient soil cations to form insoluble salts. In natural ecosystems, plant communities rely on mycorrhizal fungi to access these forms of phosphorus.

Mycorrhizal hyphae produce enzymes, including phosphatase to convert phosphorus into soluble, plant-usable forms. This same process can be valuable in agriculture, maximizing the availability of natural soil P as well as dramatically enhancing the efficient uptake of P derived from fertilizers. With greater P uptake, costs go down and yields frequently increase as well.

The availability of nitrogen can also be a factor in limiting crop productivity for reasons opposite to those limiting P. Available nitrogen in the forms of nitrates (N03), nitrites (N02), and ammonium (NH4) are very soluble and can flow past the root zone before roots can absorb it. This means they are often lost to run-off or groundwater or trapped in subsoil beyond the access of roots.

The profoundly dense network of tiny hyphae filaments in a mycorrhizal system typically extends 45 to 60 centimeters beyond the roots themselves, increasing the absorptive surface area of colonized roots hundreds to thousands of times. A teaspoon of mycorrhizal soil can easily contain several kilometers of hyphae, all of which are highly absorptive of soluble nitrogen ions, ensuring optimum uptake and the associated nitrogen-related cropping benefits.

Another source of nitrogen uptake unique to mycorrhizal symbiosis has recently been discovered by scientists at the University of California, Irvine, US. The researchers set out to explore how nutrients, including nitrogen, are mobilized through the environment. Using cutting-edge technology, nanometre-sized bits of a semiconducting material called quantum dots were attached to organic compounds such as nitrogen-laden amino acids.

Nutrient transfer discovery

When energised by an ultraviolet laser, the tiny dots emitted light, becoming detectable by special cameras positioned in the root zone of plants. In this manner, the scientists could track nutrients as they were absorbed into the microscopic mycorrhizal hyphae and follow their subsequent movement into the tissue of the host plant.

For more than 100 years conventional scientific wisdom held that root absorption of nitrogen was restricted to inorganic forms of nitrogen such as N03, N02, and NH4. But to their surprise, the scientists saw the illuminated dots attached to amino acids enter the mycorrhizal hyphae and observed them as entire molecules moved into the root cell vacuoles and then continued systemically to the chloroplasts (in which nitrogen is used for photosynthesis).

MYCORRHIZAE

In non-mycorrhizal rhizospheres, amino acids, which are the primary components of proteins, must undergo extensive and time-consuming decomposition processes by bacteria and other soil organisms before nitrogen is released in inorganic, plant-usable forms. In many cases, much of the nitrogen is consumed by the organisms, further delaying its plant availability.

This research demonstrates that mycorrhizal fungi allow their plant hosts to bypass this process, implementing quick and effective access to organic nitrogen sources. What this means to the farmer is that utilizing mycorrhizal fungi, naturally occurring and introduced sources of organic nitrogen (such as found in fish-based fertilizers, green manures, and compost) can provide a readily available source of nitrogen to promote crop growth and enhance yields.

In addition to phosphorus and nitrogen, the mass of hyphal filaments in the soil surrounding mycorrhizae-colonized roots is also capable of mobilizing an array of other important plant nutrients, including calcium, iron, magnesium, and critical micro-nutrients such as manganese, zinc, and copper. Just as a lack of vitamins can impair human or animal health, crop yields and forage production are sometimes limited by insufficient supplies of these minor- and micro-nutrients, even when N-P-K is abundant.

Mycorrhizae’s ubiquitous presence throughout the surrounding soil can access these relatively scarce resources and, in many cases, can release them from insoluble compounds via the production of specialized enzymes. The management of micro-nutrients is becoming increasingly recognized as an important component of modern cropping science. Mycorrhizal fungi can serve as a useful tool to ensure that both natural and introduced sources of these nutrients are transferred efficiently from the soil to the plant.

Help find water

Mycorrhizae’s significant assistance with nutrient uptake is important, but it is not the only crop-enhancing benefit offered by these amazing fungi. Another valuable feature is water management. The expanded and enormous absorptive surface area connected to the roots is going to ensure that nearly all moisture in a plant’s surrounding soil is accessed. But what then? Once the soil is dry, how can the plant survive?

Mycorrhizae provide a mechanism inside the root cells that addresses this problem. When a root cell becomes colonized by a mycorrhizal fungus, a special shared organ called a vesicle grows inside the root cell. The vesicle is essentially a storage container for water and dissolved nutrients that can be utilized in times of deficiencies, such as drought periods.

When moisture and nutrients are abundant in the soil, surplus supplies are stored in the vesicle. When moisture and/or nutrient shortages occur, the plant begins to utilize the resources stored in the vesicles to avoid stress for extended periods – often weeks or even months longer than non-mycorrhizal plants.

When moisture or nutrients again become available, the plant is able to return to normal, healthy respiration and growth without shock or other negative symptoms. Of course, the reservoir provided by the vesicle cannot last indefinitely and the plant will suffer stress and ultimately death if sufficient moisture or nutrients remain unavailable for too long.

However, in most cases the extra non-stressed time provided via the vesicle allows the plant to survive until the next rainfall. This is great news for the dryland farmer. Australia’s recent excessive rainfall notwithstanding, drought is a serious risk encountered by all dryland farmers. Although not infallible, mycorrhiza inoculation offers inexpensive crop insurance as one of its many benefits.