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The grazing resource

K.J. Hutchinson

CSIRO Division of Animal Production, Private Bag, Armidale NSW 2350

Summary. Australia's sheep and cattle industries provide more than half the value of our national agricultural production and these industries are based almost entirely on grazing. However, there is a growing perception that our grazing lands are degrading (7) and there are major problems in planning their sustainable development. The main goals of agronomic management must be to conserve the bio-physical soil resource, to develop and to stabilise a nutritious mix of plants that are well-adapted to climate and to grazing, and to optimise productivity by the effective acquisition, uptake, recycling and retention of mineral nutrients. The components of the grazing ecosystem and the enterprise are defined along with parameters of system behaviour. Problems of degradation and the potential for further development in the semi-arid, high rainfall tropical and the high rainfall temperate zones are reviewed briefly and the complexity of management is illustrated by case studies. Agronomists, economists and educators will need to develop and to apply an ecosystem perspective to meet all the challenges of ecologically sustainable development (6).

The distribution and development of grazing lands

Sixty-one per cent of Australia's total land area of 768 million hectares is grazed by sheep and cattle, whereas only 3% is used for broadacre cropping. The gross annual return from ruminant products exceeds $12 billion, which is more than half the value of Australia's total agricultural production (16). Native grasses and shrubs comprise 94% of our grazing lands (Fig. 1) but support only 59% of our livestock numbers, expressed as sheep equivalents (344 million in 1990-91). Arid and semi-arid rangelands occupy 383 million hectares and there is a further 27 million hectares of native grasslands in higher rainfall regions (25). The carrying capacity of domesticated stock on native grazing lands varies widely with from 30 to 0.5 hectares of land being used to support one sheep equivalent (4).

Figure 1. (a) Areas (%) of native and improved grasslands, and (b) Livestock carried (%).

Only 6% of our grazing lands have been improved by the introduction of exotic plant species and the use of fertiliser, yet these improved pastures support 41% of our domestic livestock (Figs 1(a) and 1(b)). Approximately 80% of Australia's total sown pastures have been temperate and mediterranean climates, where plantings began in the 1920s and peaked in the mid-1970s. These pastures are predominantly legume-based, with the dominant species being subterranean clover, Trifolium subterranean, white clover, Trifolium repens,lucerne Medicago sativa, and barrel medic, Medicago truncatula. The introduced perennial grasses phalaris, Phalaris aquatica, ryegrass, Lolium perenne, cocksfoot, Dactylis glomeratum, and tall fescue, Festuca arundinacea, can be major contributors to the production of the 14 million hectares of sown pastures in the higher rainfall, temperate regions.

There are 4.5 million, hectares of sown tropical pastures, including three million hectares of all-grass pastures (19). Sown, tropical pastures in Queensland increased four-fold to 4.3 million hectares between 1960 and 1990. The major tropical legumes currently being sown are Caribbean stylo, Stylosanthes hamata cv. Verano, shrubby stylo, Stylosanthes scabra cv. Seca, round leaf cassia, Cassia rotundifolia cv. Wynn, and jointvetch, Aeschynomene americana cv. Glenn. Use of a number of earlier introductions has declined because of disease susceptibility and higher management requirements (21). The major sown grass species are silk sorghum, Sorghum spp. hybrid cv. Silk, Rhodes grass, Chloris gayana, buffel grass, Cenchrus ciliaris, signal grass, Brachiara decumbens, and purple pidgeon grass, Setaria incrassata. There can be large increases in the production of sown grasses when nitrogenous fertiliser is applied suggesting that the level of nitrogen fixation by companion tropical legumes may be inadequate (17).

Grazing ecosystem and enterprise

The major components of the grazing ecosystem and the individual enterprise are given in Figure 2(a). Internal components of the ecosystem are animals, plants, other biota and the mineral soil which act together to support the production of the grazing animal. External components are a variable climate and a range of inputs and decisions associated with management. Australia excels at low-cost and efficient management of ruminants but neglects the regenerative needs of the grazed plant, which is often selectively grazed year-long, even under climatic stress. While the farmer is familiar with the condition of animals and pastures, he is less informed about bio-physical function in the top one-metre of soil. The interactive effects of treading and rainfall can damage the plant, reduce water intake and the habitat for biota that recycle nutrients from organic residues. Impaired physico-chemical and biological fertility in the soil may be important though less visible sources of long-term production decline. Finally, an overlay of marketing, economics and societal factors must be integrated with biological productivity to constitute the grazing enterprise.

Figure 2. (a) The grazing enterprise, comprising the ecosystem overlaid by economic and societal factors and (b) Motivation and the setting of short and desirable long-term priorities by farmers.

Scott (18) drew attention to farmers ranking of short-term priorities from profitability (highest) to soil care (lowest). These parallel motivational theory (14), which ranks human priorities from food and shelter (highest) to the meta-needs of altruism and self-actualisation (lowest). Scott's triangular presentation is extended in Figure 2(b). by adding the community interest to the base. Pressures from factors such as drought, low prices and a high debt to equity ratio focus priorities on dollar returns at the top and the enterprise must be able to cope with such stresses by a designed resilience, both biological and economic. Thus, over the longer. term, opportunities must be taken to extend priorities down the triangle, by making management and investment decisions that will sustain and improve the bio-physical stability and the asset value of the enterprise. Flexibility to respond to market change is also a necessary attribute of sustainable development. Finally, the interests of the community will become more important as people become more aligned to the national objective of environmentally responsible land care. However the altruism of the manager alone will not suffice and new policies will need to be considered. Possibilities are:

  • information, education and group action;
  • pricing policies, subsidies and taxation;
  • property rights, compensation and regulation;
  • seeking cross-compliance between groups.

Transitional states, system parameters and inter-connections

The concept of a single and persistent vegetational climax that represents a stable 'ideal' (1) is being supplanted by the view that grazing resources are intrinsically dynamic, moving between 'equilibrial' states with the intervening transitions governed by a combination of management and unplanned events (9,23). As man demands a greater use of resources, the likelihood of significant transitions increases, particularly where there are strong interactions between management and unplanned events, such as the combination of overstocking and drought (Fig. 4). Driving forces for improvement include prescribed fire, fertilisers, introduction of exotic plant species and grazing management. Two essentials for successfully applying the concept of dynamic states are:

  • ability to predict the critical threshold for transition and its impact on sustainable production;
  • knowledge of the bio-physical mechanism(s) underlying a transition, which may enable an evaluation of the reversibility of undesirable change and the success rate of remedial measures.

Stability is the constancy of temporal change in an attribute of ecosystem or enterprise; it can be expressed as the reciprocal of the variance (3,10). However, to be of analytical use, the variation must be partitioned (e g., trend and residual) and ultimately assigned to patterns of seasonal or yearly climate, outbreaks of pests and disease, chronic decline due to grazing pressure on preferred species, nutrient limitation, loss of soil structure with impaired hydrology and loss of habitat for useful soil biota. Large changes, that follow major stress, such as drought and fire, must also be accounted for. The stability of different attributes of a system can vary widely. For example, plant production can be less stable than animal production and notably so when animals are fed supplements. Resilience is the degree, manner and rate of recovery of an attribute to its level prior to some major disturbance (22). Elasticity and amplitude are two components of resilience (Fig 3(a)). Elasticity is the rate of recovery of an attribute following a major stress. The amplitude of recovery defines a new 'equilibrial' state and thence the net change in the system.

Figure 3. (a) Components of resilience and, (b) Interconnections between ecosystem components.

Twenty inter-connections between the major internal and external components of grazing systems (20) are indicated in Figure 3(b). These can be of major importance, as a source of positive or negative feedback control, the net effects of which determine the stability of a system (12). Dynamic simulation models of agricultural systems commonly overlook important sources of feedback control, while emphasising the 'feed forward' of energy, nutrients and dollars leading towards the product and its value. In addition to the inter-connections, each of the four internal components of the grazing ecosystem can have its own strategy for essential functions. For example, plants, grazing ruminants, decomposers and the mineral soil each have internal mechanisms for retaining nutrients, based on internal cycling for the biota and sorption for soil. The relative importance of internal strategies versus external exchanges will vary both with the component and the overall nutrient status of the ecosystem. Understanding these transfers is of major importance for developing long-term, cost-effective and environmentally responsible strategies for fertiliser use.

Management practices and sustainable grazing

Management practices that can influence directly the production and stability of rain-fed grazing systems, with their major objectives, are listed below.

  • New plants and fertilisers are aimed at increasing net primary production (npp) and its feeding value for ruminants. Improved quality of organic residues also enhances nutrient cycling.
  • Choices for stocking rate, placement of watering points, fodder conservation and forage cropping, animal type and reproductive control are directed at increasing the utilisation of npp.
  • Grazing management, prescribed fire, chemical and biological control, are used to sustain desirable plant species and to control weeds, pests and diseases.
  • Exogenous feed supplements and disease control aim to benefit the domestic grazer directly.

The impact of many of these practices on temperate, sown pastures was examined intensively in the 1960s using experimental units comprising small land-plant-animal areas (mini-ecosystems). W.M. Willoughby (CSIRO, Armidale) led the questioning of the effectiveness of 'European' practices for Australian grazing systems, based on the year-long grazing of landholdings of fixed area. The latter conditions impose constraints that reduce the efficacy of many practices. Choice of stocking rate and the application of fertiliser emerged as the major determinants of animal production per unit area. Early conclusions on choice of stocking rate were based on short-term optima for production per hectare. However, when additional factors such as variable costs, risk minimisation, income satisfaction (24) and a likely decline in production optima with time (5), are included, the outcomes are more likely to favour a conservative stocking policy. Fertiliser studies in the 1960s also focussed on short and midterm response. In the 1990s, following 20 to 40 years of fertiliser use in many temperate grasslands, the mass movement and balance of nutrients may provide a better criterion for determining long-term fertiliser strategy.

While the whole system studies of the 1960s contributed substantially to knowledge of factors and their interactions, which govern production responses in sown, temperate pastures, there was a general lack of awareness of sustainability issues, such as:

  • the need to manage for botanical stability in pastures;
  • responses of native grasses to fertiliser and to grazing management; the need to define land capability and to accommodate spatial variation;
  • the nature and definition of bio-physical dysfunction in pasture soils, and
  • the importance and subtlety of feedback control in determining stability.

Arid and semi-arid rangelands

Rainfall events and temperature control the primary production of rangelands (15), while management factors such as stocking rate, fencing, watering and fire affect the stability of these resources. Prolonged heavy grazing in some regions can result in the dominance of woody shrubs that are largely inedible. Major mechanisms underlying transitions from grass to woody shrubs are reasonably well-defined and include seed production, theft by ants, and conditions for the germination and the survival of shrub seedlings as they are influenced by rainfall, fire and grass competition. A combination of rainfall pattern, controlled grazing and use of prescribed fire can restore the balance between perennial grasses and encroaching shrubs (8). Reduced stocking level, by itself, is not effective, but it can provide an opportunity for prescribed fire to act as a circuit breaker. A successful burn requires at least 80 g/m2. of grass mass as fuel and the pattern of seasonal rainfall needed for this amount of grass growth may occur only once in 20 years. Harrington (pers. comm., 1991) has suggested that a lack of management experience and confidence in the use of prescribed fire, combined with the rarity of the rainfall pattern needed to grow sufficient grass fuel, may result in important opportunities for shrub control being missed.

The ecology and sustainability of grazing enterprises in the arid and semi-arid rangelands is controversial given the competing interests of pastoralists, conservationists and claims for land rights by aboriginal Australians. Pastoral enterprises differ widely in their bio-physical and economic viability and, while differences can be associated with the major vegetational associations, there are insufficient data for developing process-based models on which to develop land use policy. However, a linear judgement model has been developed that is based on assessments by an expert. Viability prospects (VIPROS), for 10 major regions, were assessed on vegetation type, vulnerability to overgrazing, the contribution of valuable perennials, soil water holding capacity, rainfall pattern, transport distances and economic solvency over 20 years, assuming a moderate stocking policy to avoid both vegetational degradation and waste (2). A comparison between the model's output and existing land use suggested that 65% of grazing enterprises in arid and semi-arid rangelands had medium to high prospects of viability and that the remainder should be withdrawn from pastoral use (25). While this may not be feasible, politically and socially, the findings do indicate that use of marginal land should not be expanded. However, prospects for expansion and development are considerably better in the higher rainfall regions.

Temperate and tropical grazing lands in higher rainfall regions

At the time of European settlement, the grassland associations in temperate regions appear to have been well-adapted to drought, occasional fire, low soil nutrients and grazing by macropods. Tall, warm season, perennial grasses, such as Aristida ramosa, Themeda australis, Sorghum leiocladum and Poa sieberana were dominant depending on soil texture and elevation (13). With the introduction of sheep, these species tended to be replaced by short, warm-season perennials such as Bothriochloa macra and Sporobolus elongatus along with cool-season annuals. With grazing, Aristida ramosa and Danthonia spp. remained prominent in soils of light and heavy texture respectively. With the increased use of superphosphate, particularly since the 1950s, and an accompanying increase in ruminant numbers, there have been increases in the more nutritious native grasses (year-long green) such as Microlaena stipoides and Danthonia spp. and exotic legumes, notably 7'. repens and T. subterraneum. These plant associations, termed semi-improved pastures, can be developed cost-effectively and can be promoted by grazing management (13).

With increased fertiliser use, there has also been a significant investment in all-exotic temperate pastures, commonly sown into a prepared seedbed. These fully improved pastures were highly productive in the 1960s and 1970s, but evidence is growing that they are now in decline with poor persistence of sown species and the ingress of less productive annuals. The trend is particularly apparent under set stocking. An example of this lack of stability is provided by 28 years of data on botanical change in improved pasture, sown with phalaris cv. Australian and white clover cv. Huia, well-fertilised and set-stocked over a wide range of rates (11, Hutchinson and King, unpublished data). Changes in the sown perennial grass versus other grasses, mainly annuals, are shown as stability diagrams, which present changes viewed through a 28-year 'time corridor' (Fig. 4). With a low stocking rate (10 sheep/ha), the phalaris was relatively stable, with a ratio of perennial to annual of about 3:1, and satisfactory recovery (resilience) after a severe drought in 1965. However, the medium treatment (20 to 15 sheep/ha) showed little resilience and 'stabilised' post-1965 at about 1:1, with a further increase in annuals after a second major drought (1980-82). At the high stocking rate (30 to 20 sheep/ha), the system showed no resilience with the phalaris replaced almost entirely by annuals. Major factors underlying this strong interaction between set-stocking rate and drought would appear to be selective and yearlong grazing for the phalaris, with reduction of its budbank, and the lack of grazing control to provide for its successful regeneration. Some decline in the bio-physical structure of the soil with stocking rate was also observed, but nitrogen status did not appear to be a major factor. If the sown perennial can be sustained, it will generally provide strong competitive exclusion of annuals.

Figure 4. Approximate stability and resilience behaviour, over 28 years, of phalaris versus the ingress of other grasses. Sites were set stocked at three rates (text) and experienced two major droughts.

Tropical grazing lands also have considerable potential for further sustainable development with more than half an area of 22.1 million ha of easily attainable sown pasture in Queensland remaining unimproved (21). Cattle production can be limited severely by low quality residues from tropical native grasses. These residues can be used more effectively if cattle are supplemented with nitrogen and phosphorus, and this practice has resulted in substantial increases in cattle production in the last decade. However, an increased utilisation of grass residues can destabilise these systems and drought assistance can exacerbate the problem. A loss of grass cover from over-utilisation has led to soil loss and siltation in the Burdekin catchment and reduced the opportunity for prescribed fire to control shrub encroachment (5).

There are common goals for sustaining grazing enterprises and these apply generally from rangelands to sown pastures although problems and priorities vary. Objectives, for planning ahead, in addition to the good husbandry, hygiene and welfare of livestock, are to:

  • conserve the soil resource and its bio-physical structure;
  • enhance soil fertility, nutrient cycling, and the retention of nutrients;
  • sustain nutritious and productive plants that are well adapted to climate and to grazing;
  • optimise forage use, within the constraints of responsible soil and vegetation management;
  • monitor and analyse change in plant and soil resources;
  • develop grazing enterprises that are resilient, adaptive to stress and to market change;
  • assess the long-term benefits and costs of sustainable resource use and development.


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