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Chapter 5 - Summary of physical, biological and management aspects of dryland cropping

Lessons for dryland cropping systems
The balance of future research and development

This chapter draws together and summarizes the various physical, biological and management aspects arising from knowledge of the biological mechanisms which underlie soil and crop management (Chapters 2 and 3) and present cropping practices (Chapter 4). It also draws attention to some unresolved issues and the diverse lessons that have been learned. Some of the views outlined below are broadly accepted, but others may appear contentious or contradict accepted wisdom. In the final section, selected issues are raised because they require more debate and resolution before policies are developed and resources found to deal with them.

Lessons for dryland cropping systems

Need to import nutrients
Need for realistic pricing to encourage better crop and management choices
Participation by farmers and their responsibility for land care
Measurement of cropping sustainability
Desirability of matching biological solutions to local circumstances
Appropriate soil management and the use of fallows
Need for more legume crops
Weeds, pests and diseases as indicators of management expertise

Need to import nutrients

It is emphasized above that there is usually marked spatial variation in fertility within a farm. Further, modem markets ensure that crops, livestock and their products are exported from farms, including those in dryland regions, to sustain largely urban populations elsewhere. In this way, nutrients are being removed at faster rates than they are replenished through soil mineralization.

Such nutrient export is of no concern as long as soil and crop resources are conserved by importing nutrients regularly to balance the losses (e.g., Table 47). Thus, a biologically sustainable dryland cropping system could require an annual off-farm input of say 1.8 kg P/ha to replace that removed in grain and residue from a 600 kg/ha grain crop. Looking at it another way, a 2 t/ha grain crop (an appropriate target where there is 200 mm rainfall during the growing season), requires 6 kg P/ha to replenish that removed in the crop. This assumes a water-use efficiency of 10 kg grain/ha for every millimetre of rainfall, and that 30 g P/ha should be applied for every millimetre.

Though there are no qualitative, generic differences in biological sustainability across semi-arid regions, some systems appear inherently more sustainable than others. Examples include sparsely-populated mechanized systems in Australia and USA where farm surpluses are usually sufficient for farmers to afford inorganic nutrients. Thus, with respect to dryland cropping in developing countries, the question is not simply how to help to make it biologically sustainable, but can economic signals or support mechanisms be developed (e.g., subsidies from city-dwellers) that cause local farmers to act rationally in economic terms and encourage them to maintain the sustainability of their soil and cropping system. Jolly (1989) draws attention to the relationship between the farmers' economic environment and their decisions about fertilizer use. Put another way, the challenge for agricultural policy-makers is to make economics coincide with soil sustainability.

Economic analysis of cropping systems tested for rainfed black soils in NE monsoon season (Source: Palaniappan 1985)

Cropping system


Gross income (Rs/ha)

Cost of cultivation (Rs/ha)

Net income (Rs/ha)

Return per rupee invested (RS)

Sole safflower






Sole bengalgram






Sole coriander






Sole wheat






Safflower + bengalgram






Saff lower + coriander






Saff lower + wheat






Bengalgram + safflower






Bengalgram + coriander






Bengalgram + wheat






FIGURE 40 - Overview of the framework for economic analysis of tillage alternatives (Source: Stonehouse 1991)

As an illustration of the kind of economic circumstances that could be developed to achieve biological sustainability, European governments wishing to have national food security and valuing an inhabited scenic countryside, may be prepared to subsidize both food production and countryside management, thereby making cropping economically and biologically sustainable. Developed countries and, perhaps, those developing countries with sufficiently-wealthy urban populations, may take a similar philosophical view of their semi-arid croplands. It may be better to provide marginal support through fertilizers or recycling of city wastes to maintain long-term biological and economic sustainability of dryland cropping than to devote greater resources to social issues such as migration, particularly if such issues are associated with loss of sustainability. If such a transfer of resources from cities to cropping systems, is seen to maintain sustainability (Table 1), and as the best and least cost option, the question becomes not 'What can be done?' but which is the best source of nutrients - inorganic fertilizers or organic city wastes.

Need for realistic pricing to encourage better crop and management choices

Biological sustainability is currently compromised by the need for short-term economic sustainability; the question arises: how can economic signals or support mechanisms be developed which will cause farmers to act economically yet maintain the sustainability of their cropping system? It is clear that the most suitable rotations are those that include leguminous grain, forage and tree crops and those that take a long-term view of soil management, for example by retaining soil cover rather than feeding everything to livestock. To encourage farmers to take rational economic decisions and be biologically responsible, the relative prices of agricultural products need to be considered, and systems-based budgeting is required.

Table 48 illustrates the dilemma by giving an economic analysis of a range of crops for India. Coriander has substantially the highest gross income, highest net return and highest return per rupee invested. Sole cropping of coriander might logically follow. The second most attractive option, coriander intercropped with the legume bengal gram, would not be grown if farmers made their cropping decisions based only on the likely profit of their next crop.

In the absence of regulations, sustainable crop rotations could be encouraged by: (a) the artificial manipulation of grain legume prices; (b) a market rise in the relative prices of grain legumes, associated with increasing scarcity of other protein sources (e.g., livestock, fish); and (c) by the preparation and promulgation of full budgets that include the indirect and residual benefits and costs of various crop rotations.

There is a real need for greater use of systems-based budgeting in both developed and developing countries. Figure 40 gives a schematic example of the components of such a budget for tillage. It takes into account all costs, including the direct variable costs which determine net returns to the farmer in the year under consideration and the indirect (usually un-measured) on-farm costs such as erosion and external costs, for example, watercourse pollution. Assessing indirect and external costs gives farmers a more realistic base for their on-farm decisions, and politicians and the public greater knowledge of the real environmental costs of farmers and policy-makers continuing to act to maximize short-term profits.

Participation by farmers and their responsibility for land care

Farmers need to recognize the indirect and external benefits of sustainable cropping if they are to manage their land 'with care'. They can be encouraged to meet formally or informally to discuss and develop sustainable cropping practices. The Land Care and Total Catchment Management groups of the Australian Murray-Darling basin are a good example of an appropriate farmer-based initiative (Watkins 1991).

By contrast, government management directives, subsidies and taxes may be ineffective or inequitable. Furthermore, where government directives are applied, for example to avoid pollution of waterways, there is a responsibility, not always exercised, to assess the impact of the directives on the whole cropping system. To give one example, if the government was to prohibit the use of fire to manage woody weeds in western New South Wales, Australia, it is estimated that it would be necessary to increase the size of each property by 80% to compensate for loss of income (MacLeod 1990).

Measurement of cropping sustainability

In Chapter 1 (Figure 1) it is suggested that sustainability can be measured by the rate of resource change (degradation), forcing, inertia, elasticity, and amplitude. It seems that the concepts of the rate of resource change and forcing are the most practical. The easiest aspects of forcing to estimate are subsidies from the non-agricultural sector and inorganic fertilizer input. Useful aspects of resource changes are many. They include vegetation (plant population and diversity), soil colour and texture (these can be scored by farmers), soil chemical attributes (e.g., pH), and pollution of groundwater or surface drainage from a farm.

The process is more important than the key indicators eventually chosen. Figure 4 suggests how key indicators of the sustainability of crop rotations for particular areas can be chosen. A move to sustainable cropping will only take place if all participants (farmers, researchers, extension officers, policy-makers) are involved in selecting what is to be measured. The process is one of farmer education. One of the best ways to ensure the farmers' commitment is to establish that they are in charge of the process and have the responsibility for monitoring sustainability.

Delegating responsibility to farmers raises two issues: (a) how are spatial and temporal variability, and externalities accommodated; and (b) what measurements should be chosen?

Farmer-led measurements may give some variability in scoring, though this assertion assumes, without much justification, that external judgements, e.g., laboratory analyses, are accurate as well as precise. Given that the quest for increased sustainability involves changing farmer attitudes, does it matter if one village uses a different yardstick, or is more attuned to problems, than its neighbour, provided that both are becoming increasingly aware? Further, it is likely that small differences in climate and soil resources, and subtle differences in markets and social values, may mean that it is not appropriate for individual villages in a region to emphasize the same measures of sustainability. This leads to the proposal, consistent with Dixon (1992), that it may be more helpful to talk in terms of spatially dispersed cropping system domains, rather than large contiguous zones based on climate.

If farmers are to control the development of sustainable systems (and is there, realistically, any alternative?) then the choice of key indicators of sustainability is severely constrained. As suggested earlier there are many indicators of soil structure, biological and chemical condition to choose from. These include visible indicators of soil physical problems (Chapter 2, section Field indicators of physical problems) and soil fertility (Chapter 3, section Field indicators of biological and nutritional problems and Table 33). Given the constraints of farmer education, interest, time and equipment, the choice is limited to a few surrogates such as: (a) plant population and species diversity (Figure 17); (b) scoring soil colour, texture and hardness; and, perhaps, (c) biennial measurement of topsoil pH. Through measurements, farmers would become increasingly aware of interrelationships within their cropping systems, and reflect on issues such as the impact of erosion and loss of topsoil. Education, through measurement and reflection, might increase local expertise to the point of impact assessment. This is illustrated in Figure 5.

This participatory approach contrasts with the wide support by scientists and policy-makers of the need for minimum data sets. Because of their analytical complexity, these have to be the responsibility of external experts and remote laboratories. The contrasts between the analytical and participatory approaches are so great that discussions will be needed to resolve which method, or mixture of methods, is locally appropriate

Desirability of matching biological solutions to local circumstances

In the fifth premise in Chapter 1, it is suggested that 'It is better to tailor the understanding of generic mechanisms to local situations than to apply prescriptions for one cropping system to another'. It is instructive that rotations have broken down and cropping systems have become unsustainable in developed countries as well as in those parts of Asia and Africa described in Chapter 4. Various crops have been transferred from one system to another, but they are not always the answer to local human goals. To return to Figure 1, these goals include food security and profit, so markets and processing need to be considered if new crops are to be introduced. The goals also include satisfaction.

The characteristics of sustainable rotations are outlined earlier (e.g., Table 47), as are the options for maintaining soil physical properties (Table 19) and soil biology and nutrition (Table 34). Some of the desirable crop attributes suggested in Table 12 vary from those in previously-published lists. This might provoke thought. Table 49 summarizes the views of Reijntjes et al. (1992) on many of the aspects listed in Table 12 and relates them to crop rotations. Much work remains to fine-tune these broad recommendations to specific, spatially-dispersed, cropping systems.

Choosing crops for rotation (Source Reijntjes et al. 1992)

A crop rotation should meet the needs of the particular farm for which it is designed, and it should meet the requirements for sustainability.

Needs of the farm. When designing a crop rotation, some questions that should be asked regarding the needs of the farm are:

· Is there a market for crops in the rotation?

· Are the crops suitable for the soil types on the farm?

· Are the crops suitable for the moisture and climate conditions of the farm?

· Can the crops be produced with the equipment available on the farm or with minimal changes in equipment?

· Do the crops supply the on-farm feed and on-farm green manure needs as well as the farm's cash and subsistence needs?

Requirements for sustainability. The crop rotation requirements for sustainability revolve around the following principles:

· Does the rotation provide effective week control?

· Does the rotation provide a balance of crop production and soil conservation?

· Does it contribute to soil building?

· Does the rotation include root systems that penetrate soil compaction, bring nutrients to the surface and allowing air and water to infiltrate the soil more readily?

· Does the rotation provide for effective insect and disease control?

· Does the rotation effectively utilize available moisture? Are moisture-conserving practices included? Are high moisture users alternated with plants requiring less moisture?

· Does the rotation provide for a sufficient diversity of crops to increase stability and therefore minimize risks?

· Do the crops avoid any buildup of undesirable elements?

Appropriate soil management and the use of fallows

There is substantial experimental data suggesting worthwhile long-term benefits from: (a) the retention of crop residues on the soil surface; (b) minimum tillage; and (c) in some situations, permanent ridging (Chapters 2 and 3). These practices may not give immediate benefits. Desirable conservation practices can be introduced where there is no short-term cost (relative, say, to traditional tillage). Where, however, the long-term benefits incur short-term costs, there is a return to the need for whole-system budgeting and the introduction of appropriate financial incentives for long-term soil care.

Chapters 3 and 4 question the benefit of fallows particularly as they are sometimes regarded as a pre-requisite for rotations. Fallows long enough to develop woody vegetation and high levels of soil organic matter, in the absence of livestock, no doubt have beneficial effects in traditional bush fallow-crop rotations (Chapter 1). Short-term fallows in which the soil is kept bare to conserve water for the next crop, may also have their place but only where soil structure is not degraded by repeated tillage and grazing. Short fallows are also valuable where they are managed as legume leys, to increase soil nitrogen and organic matter and improve soil structure. Under the traditional well-managed Australian system (Figure 21) such leys provide high-quality stock feed. Poorly-managed one or two year (or, perhaps, longer) fallows within intensive dryland crop rotations are, however, too short to build up significant soil organic matter. The style of management may be inappropriate, irrespective of the duration. Such fallows may be characterized by significant bare ground, a mixture of weeds that seed uncontrolled (Table 47), heavy treading, grazing, and removal of nutrients by livestock. These fallows do not increase the sustainability of the system.

Various workers 'build in' requirements for fallows, for example: 'the prime reason for incorporating fallows into crop rotations is to enhance sustainability of production through maintenance of soil nutrient fertility" (Kassam et al. 1991). Instead, this Bulletin draws attention to management of the fallow as an indication of the sustainability of the whole system (Table 47). It follows, though this is not conventional wisdom, that in densely-populated areas, planners should encourage: (i) de-stocking and conversion of fallows to managed crop land; or (ii) the inclusion of well-managed legume forage crops between the main crops. Such actions should increase, rather than decrease, the sustainability of the whole system.

Need for more legume crops

The beneficial effects of effectively-nodulated leguminous crops are reviewed above. They need to be used more in dryland crop rotations. Such recommendation is not new. Over ten years ago an FAO workshop (FAO 1982) recommended 'research and application programmes that will lead to achieving the full potential of symbiotic and asymbiotic nitrogen fixation techniques in developing countries of the Near East Region. These programmes should include enhancing biological nitrogen fixation through:

- introduction of legumes, particularly those having a high nitrogen-fixing efficiency;
- legume inoculation using highly-efficient strains of rhizobia;
- algalization of rice fields;
- propagation and adaptation of azolla/blue-green algae systems when and wherever possible; and
- reduction of genetic and physiological constraints that limit the nitrogen fixing process.'

Since 1982 there has been more awareness of the opportunities for nitrogen fixation, both through symbiosis with Bradyrhizobium and Rhizobium and from free-living, nitrogen-fixing organisms. Much research is underway to exploit such symbioses in dryland cropping. Three particular fields of study are the development of promiscuous host plants (able to accept colonization by a wider range of native soil organisms than previously); genetic engineering of elite bacteria; and the development of new inoculation techniques. These together should produce low-cost, highly-effective rhizobia applied as a coating on seed.

Weeds, pests and diseases as indicators of management expertise

Weeds, pests and diseases are part of the cropping system. In order to establish truly sustainable systems, there should be a change in the way of thinking, by taking account of weed, pest and disease cycles (Figures 26 and 27) rather than simply reacting when pest and disease damage becomes obvious, for example, by changing the next crop. Hearn and Fitt (1992) provide a good example of this kind of new approach. Consideration of weeds, pests and diseases should play a key role in planning back-to-back grain/legume cropping. The dry-season and fallow vegetation should be managed with weeds, pests and diseases in mind. This is increasingly being seen to play a role in the management of soil condition.

The balance of future research and development

Recent research can be divided into two kinds: (a) with, and, (b) without farmers' involvement. The latter, to be effective, should support on-farm research, and not be independent of it. There are many variations on the theme of complementary on-farm and off-farm research. Chambers' proposed the 'farmer first and last' cycle has been employed and evaluated in developing countries (e.g., Merrill-Sands et al. 1989). It has been developed also for working with farmers in mechanized agricultural systems (e.g., Ison and Ampt 1992). Chambers and Ghildyal's list of researchers' attitudes when working with farmers rather than for the benefit of farmers is worth attention. A truly participatory approach involves farmers from the outset and includes them in formulation of the research design and the identification of key indicators of sustainability. Researchers learn from farmers, for instance, by comparing the efficiencies of various practices (Haen and Runge-Metzger 1989). They in turn educate farmers, for example, in the relationships that underlie soil sustainability (Chapters 2 and 3) and facilitate farmers' own learning in various ways, mainly by encouraging formalized observation and recording of indicators of soil structure.

Research not involving farmers has burgeoned in the past decade, driven largely by rapid advances in technology, notably in computerization, remote (satellite) sensing of vegetation, geographic information systems and most recently, expert or decision support systems. FAO (1983) and Diepen et al. (1991) review methods of land evaluation.

Remotely sensed or derived data provide valuable insights to the constraints to crop rotations. For example, the climatic analysis in Chapter 1, section Drylands, is based, arguably for the first time, on comprehensive meteorological data, while multi-layered geographical information systems can be used to propose land uses. Kassam et al. (1991) make quantitative assessments of crop duration, firewood requirements etc., and suggest land uses in Kenya. Diepen et al. (1989), for instance, offer maps of Zambia, showing variability in crop yield on the basis of rooting depth and available soil water and other inputs. One of the greatest constraints on dryland cropping may be uncertainty about the actual start of the growing season, so that risk-averse farmers delay planting and the crop fails to utilize available soil water and mineralized nitrogen. Satellite sensing of the reflectance of vegetation can now detect seasonal changes in greening in semi-arid environments (Figure 4 la) so that the start of the season, and its year-to-year variation, can be quantified (Figure 41b).

Remotely-sensed data and computers should help to make better on-farm decisions by giving assurance that cropping intensification (e.g., Figure 6, 37) will not incur unacceptable risk. They may also lead (Stewart, 1988, 1991) to more flexible 'response' farming, though one should be cautious that flexibility does not encourage short-term opportunism that is incompatible with sustainability.

Information generated remotely will inevitably be used to help to make land-use policy. Perhaps it will be most influential if it is widely published. Data on regional variations in the length-of-season, or the extent of soil degradation, could cause adjustments in market prices for land. Thus, an economic incentive could develop which, through land prices, will encourage good management.

While acknowledging the impressive achievements of 'remote' research, the author has some misgivings about the technology-driven collection of data by external experts. For example, Okpala (1992) advises that: 'The effectiveness of land management in developing countries requires an improvement in the quality of survey data and information on which such management is based. This should be the focus and emphasis of current national and international efforts...'. Perhaps so, but Figure 1 draws attention to human, as well as biological, elements in crop and soil systems. Many other workers (e.g., Deffontaines 1991, Napier et al. 1991) remind us that land management is in part a social activity. Perhaps it is time to re-emphasize the views of various researchers (Beets 1978; Merrill-Sands et al. 1989 and Friedrich 1992) that rural development ultimately depends on farmers increasing their awareness of the mechanisms which underlie their cropping systems, and taking responsibility for their sustainability.

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