|  Our Valuable Native Grasslands, Better Pastures Naturally
Proceedings of the Second National Conference of the Native Grasses Association
PO Box 199a Armidale, NSW, 2350
Conventional methods of cropping and grazing often lead to excessive removal of groundcover, a deterioration in soil quality and an increased prevalence of dryland salinity. The challenge for agriculture is to simulate the patchy and intermittent disturbance regimes found in nature, using the livestock and mechanical tools available. With appropriate land management, traditional enterprises such as grain, meat and wool production can be conducted in such a way that perennial groundcover is restored and the moisture-holding capacity, nutrient content and structural properties of soil are improved. As a bonus, symptoms of soil decline such as dryland salinity may be reversed.
Although some forms of salinity have been present in the Australian environment for thousands of years (White 1994), their incidence and extent have increased considerably since European settlement. The escalation in dryland salinity is a symptom of a landscape out of balance: an indicator that soils have ceased to function effectively in regard to their water-holding capacity.
Organic matter and associated soil microbes are necessary for soil aggregation and the formation of tiny spaces, or pores, which hold water and increase the storage capacity of the soil (Donahue et al. 1983, Killham 1994). Organic matter is also the soil component with the greatest affinity for water (Faulkner 1945). Reductions in the organic matter content, absorbency and water-holding capacity of Australian soils became evident within a few years of areas first being settled for agriculture (Robertson 1853, Bean 1916, Martin 2001) and have continued as agricultural practices have intensified (Charman and Roper 2001). These changes have resulted in the excessive movement of water from the upper soil horizons and its accumulation in lower profiles or lower landscape positions. When aquifers are confined, the accumulated water rises, bringing dissolved salt closer to the surface, where the salt is concentrated by capillary action and evaporation.
Disturbance regimes and landscape processes
The ecological literature indicates that the presence of animals and their disturbance regimes are often critical determinants of the infiltration and retention rates of soil moisture, the nutrient status of soils, microbial and plant diversity and the functioning of ecological processes at both microhabitat and landscape scales (Laundre 1993, Whitford and Kay 1999, Martin 2001). These findings are in accordance with the Intermediate Disturbance Hypothesis, which predicts that moderate or intermittent levels of disturbance enhance environmental heterogeneity and contribute to high diversity within and between species, both above and below ground (Crawley 1986, Petraitis et al. 1989, Guo 1996).
To regenerate agricultural landscapes, we need to understand and mimic the disturbance regimes observed in nature. A disturbance is any factor which affects the growth or the arrangement of soils or plants, and includes cultivation, grazing and herbicide application. Soils and vegetation deteriorate when there is too much disturbance, such as broadacre chemical application or ploughing, or when the disturbance is ongoing, such as continuous grazing (set stocking). Landscapes also deteriorate when there is no disturbance at all, for example in areas "set aside". Intermittent disturbance can optimise the functioning of ecosystem processes, enhance biodiversity and provide opportunities for soils, plants and microbial populations to regenerate rather than deteriorate.
Soil health and water balance
Landholders cannot alter the type of parent material on which soils are based. Nor can they change their property location, prevailing climatic conditions or historical salt loads. Fortunately, they can change land management practices in such a way as to rebuild porous, organically rich topsoil. This will not only help to restore water balance and control salinisation, but will also regenerate the natural resource base and enhance productivity through a multiplicity of other benefits such as improved nutrient availability.
We tend to think of soil formation as simply the weathering of parent material. The good news is that we can form new topsoil biologically at a much faster rate than it can form via the weathering process. The bad news is that on most land, erosion and soil loss are the dominant processes. How can we turn that around? To begin, we need to know what soil is.
Healthy soil is composed of rock minerals, air, water and living things such as plant roots, microorganisms, insects and worms and the organic materials they produce. However, there is little information available as to how to increase the levels of air, water and organic materials in soil. If you think about sex, you might remember that there are sex (6) ingredients for soil formation (then again, you might not).
The sex (6) components of SOIL FORMATION
- Living things IN the soil (plants and animals) and their by-products
- Living things ON the soil (plants and animals) and their by-products
- Intermittent and patchy disturbance regimes
All of the above components are essential for soil formation.
We cannot achieve components 2, 3 and 4 without components 5 and 6
- For soil to form, it needs to be living (4)
- To be living, soil needs to be covered (5)
- To be covered with healthy plants and plant litter, soil needs to be managed with appropriate disturbance regimes (6)
Broadacre disturbances like ploughing, and to a lesser extent continuous grazing, reduce root mass, soil organic matter and the living things in soil that produce sticky gums and bind soil particles together into crumbs, or aggregates. When the aggregates collapse, soil structure is lost along with the tiny pores within soil, which hold air and water and provide spaces for soil biota (Donahue et al. 1983, Killham 1994). When this was recognised it became fashionable to disturb the soil and vegetation as little as possible. Minimum tillage techniques were developed for cropping country, while conservation areas on grazed land were fenced to exclude livestock and allow Mother Nature to go about her work unhindered.
What have we learned from these experiences?
Minimum tillage represents an improvement on ploughing, but has really only slowed the rates of soil loss rather than contributing to soil formation. Fenced remnants, despite the good intent, often become havens for feral species, with losses of more desirable species sometimes observed. The factors required for effective landscape function in these situations are perennial groundcover and intermittent, patchy, soil disturbance regimes, especially those produced by animals (Jones 2001, Martin 2001). The extent, frequency and timing of these disturbances need to be varied in accordance with the requirements of different plant communities and prevailing climatic and seasonal conditions.
Techniques such as annual grain or fodder cropping into permanent perennial pastures (Cluff and Seis 1997, Jones 1999) and animal impact, obtained through herding, control over water, use of attractants, or pulse grazing (Jones 2000), are some of the tools we can use to achieve components 5 and 6. The effective use of such tools can regenerate the natural resource base, as opposed to merely sustaining it in its current degraded state.
Along the path to regenerative agriculture, we might discard many of the illusions we have about soils? Over fifty years ago (Faulkner 1945) observed that rain could not properly infiltrate and be stored, and nutrient cycles could not adequately function, in the absence of organically rich, porous topsoil. Furthermore, water moving across soil surfaces takes with it many nutrients, humic materials and fine soil particles, resulting in on-site depletion as well as off-site problems such as sedimentation and dryland salinity. Despite this knowledge, conventional soil management has continued to overlook the fundamental significance of soil life and soil organic matter.
If we turned the geological clock back several hundred million years to when the earth's surface was composed of rocks and rock minerals, but no plants and animals...there wasn't any soil either.
Sand is not soil.
Clay is not soil.
They are components of soil.
It is living things that maintain the world around us, the air we breathe, the food we eat, the clothes we wear, and our soils. Furthermore, there must be interactions between soil minerals and living things in order for new topsoil to form. These interactions need to be in an appropriate form and at an appropriate level. If disturbance levels are too high or too low, or continuous, the organic matter content of soils declines, leading to reduced levels of soil biota, air and moisture, leaving only the residual mineral soil which today characterises many agricultural landscapes.
Changing what we do and how we do it
Most people accept the premise that our grasslands and croplands aren't as healthy as we'd like them to be. Degraded landscapes are often characterised by areas of bare ground, erosion, the presence of weeds and the lack of desirable plant species. It is easy to make the simplistic assumption that removing the weeds and replanting some "better" species will solve the problems. Decades of experience have demonstrated that the simplistic approach rarely works, and that the plant species we put there can only survive with inputs such as fencing, fertiliser and ongoing weed control. Meanwhile, the interactions between animals, plants and soil biota remain out of balance because these factors have not been addressed, and the resulting shortfalls in ecosystem services, such as nutrient availability, need to be supplemented at the landholders' expense.
Landscapes are not degraded because they lack desirable species. Rather, desirable species will not flourish when landscapes are degraded. The components which are absent from degraded soils, that is, high levels of soil organic matter and high levels of microbial activity, are often not as obvious as the symptoms of soil deterioration such as lack of groundcover, lack of desirable plants, or dryland salinity. Attempts to treat these symptoms with structural works or plantations of trees, shrubs or grasses, can only be partially effective.
The challenge for the regeneration of agricultural landscapes is to find ways to implement appropriate levels of disturbance to restore soil forming processes and utilise ecosystem services to work with, rather than against, nature (Soule and Piper 1992, Jordon 1998).
Fortunately, highly effective land management techniques such as pasture cropping and pulse grazing have become available to Australian farmers over recent years. The future for agriculture (that is, for us all) will be determined by how well we learn to use these, and other tools, to restore perennial groundcover, rebuild soils and restore water balance.
Without a change in approach, the salinisation process cannot be reversed.
This paper is the result of discussions with many people who have enthusiastically shared their knowledge and experience and supplied valuable background materials. The financial assistance provided by NHT Project BD0444.98 "Ecological and Technical Support for Landcare on Rangelands" is also gratefully acknowledged.
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