Table Of Contents

Cropping Systems for Enduring Productivity

David Connor

Joint Centre for Crop Innovation, The University of Melbourne, Victoria 3010 ( and
Instituto de Agricultura Sostenible (CSIC), Crdoba 14080, Spain (


The Adelaide group of plant scientists was noteworthy for its broad view of agriculture and ecology. There was a continuum of work from the native saltbush vegetation at Koonamore to pasture improvement at Kybybolite. Colin Donald’s own work focussed on important plants of the agricultural systems of southern Australia, sub clover and ryegrass, wheat and barley, and with plant-plant and crop and community responses to environment and management. His fame lives on, especially for his proposal for a ‘Crop Ideotype’ approach to plant breeding (1). This Society held a symposium, ‘Ideotypes and physiology – tailoring plants for increased productivity’ (2), in Perth in 1990 to record the impact of that work, twenty-one after its publication. It is important to stress, however, this specific developments was a logical step from his earlier work that elucidated generally applicable principles of plant-plant competition that may have had equally great general impact on crop and pasture management (3).

People trained in Adelaide who went on to make significant contributions elsewhere also exhibited that appreciation of the continuum of agriculture and ecology. I can refer to the people with whom I have had close contact during my career but there are others whose work I have admired. My personal contacts include David Smith in Victoria with his work on pastures and weeds, Ray Specht who supervised my PhD project on weed ecology, Walter Stern for his work on crop and pasture productivity and dynamics, and John Russell and Ted Coaldrake at CSIRO Division of Tropical Pastures. That Queensland Division impressed me greatly with the firm foundation it laid for agricultural research with successive ecological studies of soils, climate, and vegetation in the Wallum, Spear Grass, and Brigalow regions.

The agricultural scene is now distinct to that faced by Donald and colleagues. That was a time to concentrate on the search for increased productivity. It was the time of the post-WWII wool boom. It was the time of the sub and super revolution and the glow of extraordinary success with micronutrient research and fertilizer design. The sub and super combination was widely interpreted as a prime example of a sustainable system. For the addition of relatively small amounts of phosphorous, and even smaller amounts of micronutrients in some places, sub clover fixed enough nitrogen to promote productive pasture swards with grass, and build organic fertility to support a subsequent cereal cropping phase. Australian agriculture was profitable and able to incorporate the new advances. The impact on the Australian economy was enormous. Smith (4) has recently presented a technical, sociological, and economic commentary on that revolution, those times, and the people involved.

In Donald’s time rabbits and erosion posed the major environmental risk to agriculture in southern Australia. Those problems are no longer at the forefront of concern. Now, we face the challenge to design and manage cropping systems that can reverse local problems of acidification, catchment-wide problems of salinization and nature conservation, global problems of population pressure and climate change, and assure food safety. The solution to this more complex challenge is made further difficult by the dramatic change in the profitability of farming that remains in continuing decline. Salary earners have largely kept pace with the increasing price of food but the returns to farming have not. Rather, those farmers that have survived have done so by expanding the scale of their operations and becoming more efficient. There is concern of insufficient investment to maintain the resource base of agriculture at a time when there is increasing concentration of profit higher in the food chain.

The objective of this presentation is to highlight the positive contribution that agronomy can make to the design of cropping systems for the future. This will include maintaining the ecological approach that was pioneered by Donald and colleagues, and displaying confidence that enduring systems are possible by the application of knowledge and technology, together with inputs to match productivity. I begin by explaining why agronomists must adopt a positive attitude to ecological principles and protect their search for productivity with sustainability from misguided criticism. I will then deal with system design and management and finish with some comments on the role of society in ensuring a sustainable agriculture.

Agriculture, ecology, and biodiversity

A change since Donald’s time is the developing view that agriculture and ecology are now separate, that agriculture has abandoned ecological principles, and that current inadequacies of cropping systems can only be corrected by adopting a ‘new ecology’. These ideas are reinforced by the frequent use of such pejorative terms as ‘industrial agriculture’. These forces can be seen in the various movements currently proposing the solution to the design of sustainable agricultural systems. I refer here to biodynamics, low input sustainable agriculture, permaculture, eco-agriculture, etc. While for agronomists the challenge in the design of cropping systems is to balance productivity and profitability with sustainability under changing environmental and economic conditions, criticism from activists mostly focuses on, or derives from, some component of sustainability, or some ecological or sociological ideology.

Agronomists should be confident that current agricultural systems are intensely ecological and that most existent ecological principles of individual and community response have been derived from them. Cropping systems are collections of plant communities that are established, managed, and renewed for the production of food and industrial products. In one ecological sense, crops are disclimaxes and so require physical, chemical, and energetic inputs for their persistence and continuing productivity – i.e. sustainability. In another ecological sense, they are natural food chains that have been simplified (shortened) to maximize productivity. Consequently, crops are less species diverse than most natural plant communities but their diversity and complexity is greatly increased by the human dimension within which they operate. Furthermore, they do contain the same productive processes and operate under the same ecological rules as natural communities. They have the same radiation, hydrologic, carbon, and nutrient balances. Only the magnitudes vary, especially in the greater extraction of carbon and nutrients. The design and management of cropping systems thus presents a complex ecological challenge requiring understanding of the same physical and biological processes that occur in vegetation generally, but to which is added a range of socio-economic and cultural issues of human communities.

Agronomists should not wilt in the face of criticism, especially when it is unwarranted. Those who attended the Third International Crop Science Congress (Hamburg, 2000) will recall the lecture by John Vandermeer who found little to admire in agronomy and looked to his colleagues in ecology to find a sustainable agriculture, concluding that it would mostly mimic the multi-species complexity of natural communities. While he was able to criticise shortcomings of current agricultural systems, he had no quantitative data with which to support his views, and unfortunately no written version was included in the published proceedings (5) to contribute to continuing discussion. I dwell on this example because eloquence and the promise of easy solutions mislead the press, the public, and politicians alike. The call for the maintenance of ecological principles in agriculture is warranted, but as Wood (6) asked, ‘which principles?’

The origin of much criticism lays in the mistaken notion in the ‘agroecological’ literature that diversity is essential for stability. While this may be the case for species diversity, i.e. as the number of species increases the effect of the loss of one species decreases, it has no functional relationship to productivity because simple and complex communities can be equally productive. There is no basis to extend the notion to the complex situation of sustainability of managed agriculture. It can, of course, be argued that species diversity is important to maintain genetic wealth but that is not only maintained within agriculture. Special collections, gene banks, and also land maintained outside agriculture also provide that service. In fact increasing productivity in agriculture is perhaps the best way to maintain the biodiversity of natural systems. Waggoner (7) and others have shown how the green revolution contributed not just to the feeding of an extra 3 b people but also spared considerable land for nature. Further gains in productivity can spare more land in the future.

Returning to the issue of ecosystem mimicry, I refer to a 1997 conference held in Williams, WA (8). The major environmental concern in WA is salinization caused by rising water tables. A reasonable conclusion is that the problem can be alleviated by increased water use and the development of storage buffers for winter rainfall. Trees are likely a part of that solution and when grown together with annual crops and pastures the result is certainly a more complex system. But is it useful to say that the new system mimics nature any more than does the annual system it replaces. More true to say that it more closely equates to the hydrological balance of the native vegetation. That may seem a fine distinction to some, but it is worthwhile to me. Once the notion of ecosystem mimicry for sustainable agriculture gets its head, the inevitable result, also seen in that symposium, is the conclusion that the ideal agriculture to which we should aim, are perennial polycultures, because that is how most natural vegetation looks. Perennials can be introduced into our current annual crop and pasture systems, either separated in or close integration, without the need to stress mimicry, especially when we search the world and not just the local vegetation for suitable species.

Design and maintenance of cropping systems.

A common misunderstanding is that the crops grown in each region are, or should be, the ones that are most closely adapted to the particular combination of soil and climate. An extreme version is the assumption that only autochthonous plants have that complete adaptation, in this case apparently forgetting the co-adaptation of pests and diseases. In fact it is tolerance to the physical and biological environment that serves to establish the range of crop options from which farmers make economic choices. From those options, farmers select the crops that are the most profitable in the long term, as determined by yield, product prices, and costs of inputs to maintain the productivity of the system. Selected crops must be reasonably well adapted to the environmental conditions but most crop producers face significant biological as well as economic risks and must develop production strategies and tactics to avoid them or minimize their adverse effects on production, economic performance, and on the resource base.

A rational objective for farmers is to adopt cropping practices that maximize expected long-term income, maintain cash flow to sustain their business, and maintain their resource base. The long-term aspect embodies the requirement for sustainability. This does not mean, however, that transient periods of resource depletion, or adoption of individual practices that are ‘unsustainable’ in the long term, cannot be part of an optimal solution. Ley farming, for example, involves the sequential accumulation and loss of soil structure and fertility in pasture and crop phases. In this case, long-term sustainability requires that soil condition is recoverable following each cropping phase. A currently topical issue concerns the use of herbicides, to which it seems, weeds inevitably develop resistance. From that perspective, herbicide use is unsustainable but that does not mean individual herbicides have no role in sustainable systems. It is rational to use herbicides sensibly and not squander them while they remain effective.

Economic survival requires maintenance of cash flow to avoid unmanageable debt, even if that means choosing less risky options that are less profitable. Risk is an important feature of cropping activities, especially of extensive, rain-fed cropping operations in low-rainfall regions. There is plenty of evidence that farmers are risk averse and further that attitudes to risk depend upon financial status. As wealth increases, or as financial instruments to ‘smooth’ variable returns become available, farmers, as other decision makers, are less influenced by the absolute degree of risk they face. Given that farmers should be expected to manage within normal ranges of climatic and economic variability, society must be prepared to assist farmers during or after periods of extreme conditions in order to preserve the resource base.

Cropping systems are therefore characterized by continual change. It has been well evident in the wheat industry, first in response to loss of fertility at the turn of the century, then to the high price for wool after WWII, and later to the low price for wool in the 1990’s. It continues now in response to different price combinations for crop and pasture products, and to problems of acidification and salinization. An important feature of change is that it is gradual. Farmers consider new methods of production when it is profitable to do so and they test new options carefully before adopting them completely. They must develop new skills and confidence in proportion to the added complexity. Generational change may be important, not just of equipment, but of farmers themselves. Pannell (9) emphasises the importance of gradual change in adoption of new systems and the requirement for those who propose change to provide predictions of economic as well as environmental outcomes.

All this explains that the optimal cropping system for each farm depends not only on its natural resources, but also on size, the returns from alternative products, the costs of inputs including labour, the interactions between component activities, the wealth of the farmer, and attitude to risk. This means that optimum solutions, and hence the associated degree of crop diversification, vary between regions and from farm to farm within individual regions. It is likely that one optimal solution is never achieved before another should take its place. The complexity and individuality of the problems require comprehensive models of cropping systems for their solution. At present, the most appropriate models are whole-farm linear, dynamic and discrete, stochastic programming models (e.g. 10). Some of these models contain strong biological interactions but, as yet, typical crop simulation models are not sufficiently comprehensive to deal with the range of environmental and management issues that contribute to the optimal cropping practice.

Increased effort in modelling is a priority if agronomists are to contribute efficiently and effectively to the design of optimal cropping systems for the future. The guidelines that derive from understanding of dryland salinity, for example, have to be converted into answers to site specific questions of what species, densities, planting patterns, and management, and all in the face of climate variability. Also to be stressed here is the need for more long-term field experiments and benchmark sites so that we can properly understand what sustainability really means. At present we rely on few experiments established long ago. There is need for new designs of new combinations and for new techniques of measurement and analysis.

Colleagues in the international agricultural system report changing attitudes to agricultural research, of resurgence of interest, and of realization that the resource base has seriously suffered. Agronomy needs to prepare itself for those opportunities with a clear and cohesive set of objectives and present them with confidence to match that characteristic of biotechnology.

Society’s role in the transition to a sustainable agriculture

There is widespread concern over the sustainability and environmental impact of agricultural production systems. At one extreme, high-input, high-yield agriculture, mostly in developed countries, is not always providing healthy products and at the same time is seen, in some cases, to degrade the natural environment. At the other extreme, mostly in developing countries, the struggle for productivity with inadequate inputs and technology is exhausting the resource base. While there is much agricultural production between these extremes that does not deserve such criticism, the signal strength for change is rising with the human population pressure and its increasing demand for food, other agricultural products, and landscape services. An inescapable conclusion is the urgent need for a rapid transition to sustainable agricultural production systems and sustainable management of natural resources (e.g. 11). Such agricultural production systems will closely integrate biological and technological inputs. Management will be demanding and will depend upon continuous measurement and recording to determine inputs, outputs, and status of the systems, to understand the bases for response to managerial interventions, and the variability of those responses to environmental and financial conditions. These systems must also capture the complete costs of production and invest what is required to sustain productivity and ecological stability – a critical question is how can this be best achieved?

One component of the answer is education. Society must learn what constitutes sustainable agricultural production and that responsibility for change resides with consumers as well as farmers. Consumers should learn to discriminate between products, not just as now on the basis of price, but also on methods of production. They should understand the techniques and implications of traceability and also how profitability is distributed between the production, wholesale, and retail sectors of the food chain. Another component is the development of mechanisms to ensure the continuing investment that the natural resource base requires. The options for this investment include, price premiums for production methods, targeted subsidies, and regulations on land use. Farmers will respond to incentives by adopting those farming methods that meet the requirements of society.

Market-based systems for price premiums require some form of product certification. Well-known examples of certification are found in various forms of organic agriculture that now attract over 10% of consumption in some developed countries and also offer market opportunities to developing countries. Organic agriculture, alone, cannot, however, be the single solution to the current, and therefore not to the predicted, world food demand. Although yields of individual crops can match those grown with inorganic fertilizers, shortage of manures and resting of land to recover nitrogen fertility considerably reduce overall effective yield. Greater yield will require the application of modern science, technology, and the judicious use of fertilisers and other agrochemicals. Certification schemes for such integrated production methods (12) are developing, driven largely by major food retailing companies, e.g. for fruits and vegetables, combinable crops, and livestock (e.g. 13). It remains to be seen how these schemes can assure adequate flow of returns to farmers and to the maintenance of the agricultural resource base. At present there is evidence that price premiums, except in the direct grower-consumer transactions that characterize the organic sector, remain largely outside farming.

Governments must be closely involved in the transition to sustainable agriculture. There are many examples of national plans and guidelines for ‘Good agricultural practice’ in developing countries, including in our region (14). The beginnings of international collaboration can be found on the FAO website as part of a project to assist developing-country members who have the combined concerns of market access and degrading resource base. Governments can provide overall coordination and also targeted subsidies for appropriate land use and production practices. This is now clearly evident in the EU which is changing its production-based scheme of farm subsidies towards production methods with specific references and financial support for rational use of water, control of erosion, improved use of native areas, and protection of biodiversity etc.

The challenge for the protection of the agricultural environment in Australia is enormous. There is no large tax base to support agriculture and as long as much of our production is exported in unelaborated form, connection to the retailing level will remain slight. The complexities of the problem were well explored by Fischer (15) and Ridley (16) at the last meeting of this Society in Hobart. It must be a continuing discussion and a basis for action. There is a clear issue, here, too, for the agriculture-ecology axis introduced at the outset of this paper. Agronomists need to play a major and visible role. As currently discussed in Australia, Environmental Management Systems (EMS) provide only part of the scope of ‘Good Farming Practice’ that is surely the framework within farmers need to operate.


(1) Donald, C.M. 1968. Euphyt. 17: 385-403.

(2) Field Crops Research. 1991, 26 (2).

(3) Donald, C.M. 1963. Adv. Agron. 15: 1-118.

(4) Smith, D.F. 2000. Natural gain: in the grazing lands of southern Australia. UNSW Press, Sydney, 225 pp.

(5) Nosberger, Geiger and Struik (eds.). 2001. 'Crop Science - Progress and Prospects'. Proc 4th Int Crop Science Congress, CABI, International, Oxford, UK.

(6) Wood, D. 1998. Ecological principles in agricultural policy: but which principles? Food Policy 23, 371-381.

(7) Waggoner, P.E. 1994. How Much Land Can Ten Billion People Spare for Nature? Task Force Report No. 121, Council for Agricultural Science and Technology, Ames, Iowa, USA, 64 pp.

(8) Agroforestry Systems. 1999, 45 (1-3).

(9) Pannell, D.J. 1999. Agrof. Sys. 45: 393-409.

(10) Kingwell, R.S. and Pannell, D.J. (eds) 1987. MIDAS, a Bioeconomic Model of a Dryland Farm System. PUDOC, Wageningen, The Netherlands, 207 pp.

(11) Ruttan, V.W. 2000. The transition to sustainable agriculture. in Nina V. Federoff and Joel E. Cohen (eds.) “Plants and Population: Is there Time”, Colloquium of National Academy of Sciences at University of California, Irvine, Dec. 5-6.

(12) EISA 2001. A Common Codex for Integrated Farming. European Initiative for Sustainable Development in Agriculture, Bonn, 10 pp.

(13) EUREPGAP 2001. EUREPGAP Protocol for Combinable Crops. EUREPGAP, Cologne, Germany.

(14) SCARM 2001. Towards a national framework for the development of environmental management systems in agriculture. AFFA, Canberra. 38 pp.

(15) Fischer, R.A. 2001. Proc. 10th Aust. Agron. Conf., Hobart.

(16) Ridley, A.M. 2001. Proc. 10th Aust. Agron. Conf., Hobart.

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