Soil/grass/herbivore synergies

Soil-grass-herbivore synergies in the evolution, productivity and resilience of bio-systems

Walter Jehne, Healthy Soils Australia

In October 2011, the earth’s human population exceeded 7 billion, and our exploitation of resources exceeded 150% of the earth’s sustainable carrying capacity. This is clearly unsustainable on a finite planet with 13.9 billion ha of land, much of it degrading, and totally unsustainable in the face of pending realities from climate extremes, the decline in oil, resource limits and our continued degradation of its soils, bio-systems and natural capital.

While we know of these problems, our urgent imperative is to implement solutions that fix them. And because we need solutions – urgently – we have to get dirty and understand Pedogenesis.

Ed: Pedogenesis (from the Greek pedo-, or pedon, meaning ‘soil, earth,’ and ‘genesis’, meaning ‘origin, birth’) is the science and study of the processes that lead to the formation of soil. This process was first explored by the Russian geologist Vasily Dokuchaev (1846 – 1903), the so-called grandfather of soil science. Dokuchaev realised that soil formed over time as a consequence of climatic, mineral and biological processes.

We need to understand how the soils and hence the bio-systems we depend on evolved and function, and how we have impacted these processes and their consequences to our wellbeing. We need to discover what we must do to regenerate them so as to secure our sustainable needs and future. To understand how soils – and thus bio-systems – formed to create the diverse, productive and resilient habitats and stable climate we found 200,000 years ago and have changed since then, we must go back 420 million years to when the earth was ocean and rock. We need to know how fungi – including 4 m giants like Prototaxoides – first colonised and solubilised rocks to sustain themselves – and bio-systems- to obtain nutrients that had become unavailable from the oceans; how these fungi formed symbioses with algae that could photosynthetically fix CO₂ and water into sugars that the fungi could access as their energy source in exchange for essential nutrients; how progressively such fungal-plant symbioses enabled vast quantities of CO₂ to be sequestered into biomass and soil humates to form the deep organic soils that supported this bio-productivity; how this organic ‘sponge’ enabled soils to infiltrate, retain and make rainwater available as well as retain and supply solubilised nutrients to support and extend the growth of such bio-systems; and how these processes enabled forests to colonise over 8 billion ha of the earth’s surface to create soils, and change the earth’s carbon and hydrological cycles and thus its heat dynamics and climate.

However, forests were often restricted in climates that were seasonally too dry or cold for growth. Perennial plants responded to this by suspending growth during climate extremes by forming deciduous foliage or underground regenerative structures for re-growth when conditions allowed. Other plants evolved growth and seed strategies which enabled them to mature rapidly as annuals.

These strategies for avoiding stress evolved relatively recently, particularly in our grasslands. They enabled grasslands to colonise most of the 6 billion ha of land that had seasonally been too dry, cold or extreme for evergreen plants, to instead form productive prairies, savannas and grassy woodlands.

Perennial grasslands with high root/shoot ratios sequestered vast quantities of carbon to form deep organic soils which conserved water and aided their growth and survival, whilst opportunistic annual grasses survived via their rapid growth and large or prolific seeds when conditions allowed.

The dry grasslands were, however, highly susceptible to fires that oxidised the sequestered carbon and often degraded soils and bio-systems back to their primary mineral or exposed condition. Hence, the spread of grasslands, particularly in ‘front line’ extreme climates and habitats, depended partly on whether the carbon that was fixed was able to be sequestered as humates to enhance soil structures, or oxidised by fire, thereby degrading these soils and their dependent bio-systems. The spread also depended on the balance between carbon bio-sequestration – which enhance pedogenesis and the productivity and resilience of the grasslands – and fires which oxidised and degraded these soils and bio-systems, and on the balance between the fungi that form humates and fires that oxidise and mineralize them.

Given that grasses are often periodically dry and dispersed and that fungal bio-digestion requires moist conditions, fires and soil mineralisation processes initially dominated this balance. However, once grasslands developed symbioses with ‘mobile microbial bio-digesters’ (i.e., herbivores) to convert dry grass into protein and nutrient-rich wastes, this balance shifted greatly in favour of fungi.

Since then, most grasslands have co-evolved close relationships with herbivores to convert grass into protein and dung which aids soil development and limits the oxidation of the grass biomass as CO₂. By raising the carbon, nitrogen and essential mineral status of soils, these herbivore and microbial ecologies also progressively raised the productivity of pastures, enabling these grassland-herbivore symbioses to extend sustainable bio-systems, often into marginal soils and extreme environments.

As such, natural grasslands must be seen not just as a type of vegetation type but as sophisticated symbioses of soils, grasses and herbivores, driven by sunshine and micro-organisms to maximize:

• the capture and retention of rainfall to support plant growth,

• the cycling of essential plant nutrients,

• the fixation and sequestration of atmospheric carbon back into stable soil sinks,

• pedogenesis and the development of healthy soil structures and processes, and

• the extension and sustainability of resilient pioneering bio-systems particularly into extreme and marginal habitats.

Thus, grasses not only grow on soils but also grow soils; and thereby productive resilient bio-systems. Consequently these grassland symbioses are a powerful tool for regenerating landscapes so as to secure our essential water, food and habitat needs as land, resource and climate stresses intensify. Our imperative is to use this tool wisely to help secure our sustainable safe future, hopefully, in time.

Australia, because of its location, with flat, old and highly weathered topography and soils, is not only the driest inhabited continent with the most variable, unreliable climate, but also has some of the most leached, nutrient-limited soil availabilities for sustaining plant growth and healthy bio-systems.

Because of these extremes, many of Australia’s natural bio-systems have had to evolve sophisticated and efficient processes to conserve and use water, as well as solubilise and cycle limited nutrients. These included the natural development of deep soft organic soils that conserved water, and a range of microbial ecologies for the efficient fixation, solubilisation, access, uptake and cycling of nutrients that underpinned pedogenesis and plant growth in these often extreme sites. This enabled highly productive and resilient natural bio-systems to colonise most of Australia’s 770 million hectares of land, despite its often adverse climate and soils. As a result, we have the apparent paradox of highly productive rainforests occurring on sand dunes of very low nutrient status and productive grasslands originally covering most of Australia’s ‘deserts’.

Europeans at first marvelled at the apparent boundless scale and productivity of ‘Australia Felix’, but their overgrazing of these fragile soils and bio-systems soon led to their rapid degradation and the collapse of many of their extractive land uses and the sectors and communities that were dependent on them. This was so much so that by the ‘Federation drought’ (1893-1904), many of the former extensive perennial grasslands across Australia had been so overgrazed that their topsoil, which contained most of their carbon and nutrient reserves, was lost – often to depths of over 1 metre – due to water and wind erosion. As a result, vast areas of inland Australia that, in 1840, had had deep, soft soils with organic contents of some 20% to depth, and had sustained perennial grasslands up to 3 metres high, have been reduced to hardened, often bare, subsoils with less than 1% organic matter and that are unable to infiltrate rain.

Agriculture over much of Australia has had to survive by farming such subsoils with water-holding capacities and nutrient reserves that are often less than 10% of their original natural condition. To sustain agriculture on such subsoils, farmers have had to add increasing inputs via cultivation, irrigation, fertiliser and bio-cides or through fallow and ley farming systems to try to sustain pastures and crops that may not reach former productivities, even with these unsustainable high inputs.

As these inputs become increasingly less affordable and as climate extremes and soil degradation intensifies, farmers in Australia and globally will need to face an inescapable harsh challenge. Can they understand and restore the pedogenesis processes that governed the natural productivity of their soils so as to regenerate their landscapes and viability or have to quit as systems collapse? More challengingly, can they accelerate the regeneration of these processes so that they can re-establish the resilience and productivity of their soils within decades, before the inevitable extremes from climate changes, soil degradation, population pressures and social stress make this impossible?

Given that we don’t have 420 million years to regenerate our soils and landscapes, we have no option but to use our understanding of these soils-grass-herbivores symbioses to try to accelerate the regeneration and productivity of our landscapes and our sustainable future. Can we, via the wise management of grasslands and herbivores, rebuild the soils and productivity of healthy bio-systems within decades so that their resilience can help buffer the climate extremes? Can we do this, not by continuing inputs and their degrading impacts, but by restoring the natural microbial symbioses to re-build the soil structures, hydrologies and nutrient dynamics that previously underpinned the productivity of our grasslands?

Can we, through these processes:

• Increase the infiltration, retention and availability of rainfall to support plant growth and buffer the often extremely highly variable natural rainfall in these marginal areas? Given that each gram of carbon can help retain up to 8 grams of additional water in that soil, can we use this to increase the conservation of water and pasture productivities?

• Massively increase the cation exchange capacity of that soil and thereby its ability to retain and avoid the leaching of solubilised nutrients essential for plant growth? Can the increased cation exchange capacity also aid in adsorbing sodium and hydrogen ions from the soil solution to reduce the excessive soluble concentrations that may limit plant growth?

• Greatly lower the bulk density, shear strength of soils, and thus aid the ability of plant roots to proliferate through soils and to depths? Can we, by increasing the volume and ease of soil colonisation by roots, increase the level of water and nutrients that is available to plants, and thereby support and sustain their growth, particularly under stress conditions?

• Enhance the level and diversity of biological niches and activities in these soils as well as the exudates from the growing roots needed to sustain them? As activities by these bacteria, fungi, actinomycetes and a wide range of larger mites, nematodes, worms and insects are critical to fixing and solubilising essential nutrients from the air and soil and in enhancing their cycling and availability, can we enhance these to sustain highly productive bio-systems, even where nutrient levels from the parent materials are limited?

• Enhance the essential buffering and resilience that enables such productive grasslands to evolve and be sustained, even on marginal soils and in extremely dry and variable climates?

If so, can we help to regenerate the health, productivity and resilience of grasslands that cover 6 billion ha of the planet, including arresting the spread and helping to regenerate the many man-made deserts?

The answer is, yes, we can. Certainly, innovative farmers are sustainably sequestering up to 10 tonnes of carbon per ha annually via their management of such natural soil-grass-herbivore synergies. While still modest relative to the over 100 t C/ha/an that are bio-sequestered by leading natural systems, this is a major advance on past oxidative losses which often exceeded 10 t C/ha/an, plus the even larger losses from the widespread erosion of organic topsoils through wind and water exposures.

Practical actions to help farmers realize such soil carbon and productivity improvements.

Given that leading farmers all over Australia are restoring their soil carbon and structures – and through that the productivity and resilience of their agro-ecosystems – the issue is to extend such outcomes, and to extend and integrate such innovations into the practical management of even 20% of Australia’s 550 m ha of rural landscape, to greatly aid their regeneration, sustainability and viability.

While the practices to optimize carbon sequestration and the regeneration of grasslands will vary depending on local conditions, best results have come from farmers who understand and aid the restoration of natural grassland ecologies.

Effectively this involves reducing adverse factors in that agro-ecosystem to optimize:

• The photosynthetic fixation of carbon by the pasture per unit area and over time,

• The polymerization of that fixed biomass microbially into stable soil humates and glomalin, and

• The supply of oxygen in soils to limit the excessive oxidation of soil carbon.

The latter can be achieved most readily by limiting the oxidation of soil carbon by reducing:

• The excessive cultivation of soils and exposure of soil carbon to oxidation and desiccation,

• The excessive use of fertilizers that kill key microbes or aid microbial respiration rates,

• The use of bio-cides that can be detrimental to microbial humate and glomalin formation,

• The burning of stubble and soils which reduces carbon substrates and can kill microbes, and

• The bare fallowing of soils which can aid oxidation and reduce new carbon substrates.

Similarly, the sequestration of carbon and pedogenesis processes can be aided by:

• Maintaining cool soil conditions via shade or insulating organic mulches,

• Maintaining moist soil conditions by limiting evaporation again via organic mulches,

• Maintaining actively growing cover crops to sustain the input of carbon substrates,

• Optimizing root exudation levels so as to sustain optimal soil carbon microbial ecologies, and

• Regulating oxygen levels to optimize these microbial ecologies and carbon sequestration.

Innovative farm leaders demonstrate how such outcomes are being achieved, for example in:

• The New England Tablelands, where holistic management has enabled the regeneration of natural perennial pastures, improved soil carbon and structures and the retention of rainfall to enable a sustained three-fold increase in stocking rates, with reduced inputs and major natural capital improvements.

• The Western Australian wheatbelt, where pasture management has similarly enhanced the carbon content, structure, water holding capacity and productivity of the sandy soil and the landholders’ ability to secure quality grain yields with lower inputs on as low as 150 mm of rainfall while avoiding the repeated crop losses on adjacent, conventionally-farmed properties.

• Central NSW, where innovative pasture/cropping strategies have created temporary growth niches in the root zone of heavily grazed perennial pastures which enable annual grain crops to be produced in a continuous integrated farming system that enhances the build up of soil carbon, hydrological outcomes and the capital value of that land.

• Dairy pastures in Victoria that have been seriously degraded by extended flood irrigation, but are being regenerated via pasture management to restore carbon levels, soil structure, water holding capacities and their productivity as dairy pastures with reduced water inputs.

• The regeneration of the western districts of NSW, where strategies for the accelerated succession of large areas of woody weeds are being implemented on remnant degraded subsoils to return these landscapes into productive perennial grassy woodlands.

The management of grasslands to aid the regeneration and health of our landscape.

As nature did 420 million years ago, humanity, via its farmers, must face its urgent responsibility to restore the health, resilience and productivity of its finite agro-ecosystems and landscapes in an increasingly harsh climate… or risk the fate of most previous civilizations: their ignominious collapse.

However, unlike nature, we have perhaps 20 years to secure and regenerate these bio-systems before their aridification, climate extremes and population demands make this extremely difficult. Fortunately, nature has given us the intelligence and one of its most powerful tools – the sophisticated symbioses between micro-organisms, grasses and herbivores – with which to do this.

This set of sophisticated symbioses between micro-organisms, grasses and herbivores:

• Helped drive pedogenesis to generate the earth’s highly productive soils and bio-systems – even with minimal inputs – on marginal parent materials and in extreme climates,

• Is needed to regenerate the 4 billion hectares of currently degraded marginal wasteland and man-made deserts that will be critical if we are to feed a projected 10 billion by 2050, and

• Is needed to help infiltrate, retain and more effectively use every raindrop that falls on these soils so as to sustain essential water, food, bio-system and social needs.

Our simple but urgent challenge is to:

• Recognise the importance of these synergies in regenerating our landscape,

• Refine our understanding of how they can be managed to regenerate landscapes,

• Extend their application to regenerate a wide range of degraded environments, and

• Secure policy recognition and support for their key role in addressing this imperative.

While Stipa, holistic managers and the wider innovative land regeneration movement have long recognised the important role of grassland ecologies in the regeneration of our landscape, it is critical that we stress the fundamental role that these processes have – and can again play – in helping to turn:

• Rock into soil,

• Deserts into sustainable productive bio-systems, and

• Extreme seasonal environments and limitations into buffered conditions that are able to support life.

We need to recognize that grass does not only grow on soils, but also grows soils. We must also recognise that our grasslands and these processes are the front line or ‘colonising commandos’ in our regeneration challenge, and that, managed wisely, they are now our only means by which to regenerate and sustain healthy productive agro-ecosystems, and thus the water, food and bio-systems essentials for the projected 10 billion population. This must happen despite our aridifying landscape, more extreme climate and finite planet.