properties of agroecosystem

Agricultural Systems 24 (1987) 95-117

The Properties of Agroecosystems

Gordon R. Conway*

International Institute for Environment and Development, 3 Endsleigh Street, London WC1H ODD, Great Britain

(Received 11 August 1986; accepted 13 November 1986)

SUMMA R Y

Agroecosystems may be regarded as true cybernetic systems whose goal is increased social value. This is achieved through a variety of strategies that combine different levels of productivity, stability, sustainability and equitability. Agricultural development thus involves making trade-offs between these properties. The point is illustrated by selected examples from agricultural history, including the origins of agriculture, manorial and modern western agriculture, and the Green Revolution in Indonesia. It is suggested that these properties may be used normatively as combined criteria for evaluating the performance of agricultural development programmes and projects.

I N T R O D U C T I O N

Agroecosystems are ecological systems modified by human beings to produce food, fibre or other agricultural products. Like the ecological systems they replace, agroecosystems are often structurally and dynamically complex but their complexity arises primarily from the interaction between socio-economic and ecological processes. Hitherto studies of agroecosystems have tended to concentrate on the flows and cycles of energy and materials (see reviews in Frissel, 1977; Loucks, 1977; Lowrance et al., 1984). While these have furnished valuable insights they have captured only a part

* On leave from the Centre for Environmental Technology, Imperial College of Science and Technology, London SW7 2PE, Great Britain.

95 Agricultural Systems 0308-521X/87/$03"50 © Elsevier Applied Science Publishers Ltd, England, 1987. Printed in Great Britain

96 Gordon R. Conway

of agroecosystem complexity and have had relatively little impact on the theory and practice of agricultural development. In this paper I suggest that agroecosystems can be characterised by a limited set of dynamic properties that not only describe their essential behaviour, but can be used normatively as criteria of agroecosystem performance and hence can be employed in the design and evaluation of agricultural development projects, at all levels of intervention.

AGROECOSYSTEMS AS SYSTEMS

Although the concept of the ecosystem is long standing (Tansley, 1935), it is often difficult to identify and characterise ecosystems in nature. Their boundaries are frequently obscure and sometimes ecosystems appear to be no more than random clusterings of weakly interacting populations. Indeed, there has been some dispute as to whether natural ecosystems are true cybernetic systems, that is, have clearly defined goals and are steered towards realising these goals by pervasive feedback control loops and communication networks (Engelberg & Boyarsky, 1979; McNaughton & Coughenour, 1981; Jordan, 1981; Knight & Swaney, 1981; Patten & Odum, 1981). Nevertheless, there can be little doubt that the transformation of ecosystem to agroecosystem produces well defined systems of a cybernetic nature.

In the transformation the great diversity of wildlife in the original natural system is reduced to a restrieted assemblage of crops, pests and weeds (Fig. 1). There is a strengthening of the bio-physical boundary of the system, a bund is created around the ricefield, for example, which makes the boundary less permeable. The basic ecological processes--competition, herbivory and predation--still remain, but these are now overlaid and regulated by the agricultural processes of cultivation, subsidy, control, harvesting and marketing. Recognisable system goals become apparent that are sought through human social and economic co-operation and competition. One consequence is that the system boundary acquires a socio-economic dimension. It is this new complex agro-socio-economic-ecological system, bounded in several dimensions, that I call an agroecosystem. At least in cybernetic terms, an agroecosystem defined in this way is more similar to an individual organism than it is to a natural ecological system.

The most widely recognised agroecosystem is the crop field con- ceptualised in Fig. 1, or the livestock paddock. But if agroecosystems are defined so as to include both ecological and socio-economic components, then we can envisage a classical hierarchy of such systems (Fig. 2). At the bottom of the hierarchy is the agroecosystem comprising the individual

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The properties of agroecosystems 99

plant or animal, its immediate micro-environment, and the people who tend and harvest it. Examples where this exists as a recognisably distinct system are the lone fruit tree in a farmer's garden or the milk cow in a stall, but it is possible to think of the individual plant in a crop population or the animal in a herd in this way. The next level is the field or paddock and the hierarchy continues upwards in this way, each agroecosystem forming a component of the agroecosystem at the next level. Near the top is the national agroecosystem composed of regional agroecosystems linked by national markets, and above that the world agroecosystem consisting of national agroecosystems linked by international trade.

Systems theory holds that the behaviour of higher systems in such a hierarchy is not readily discovered simply from a study of lower systems, and vice versa (Simon, 1962; Whyte et al., 1969; Milsum, 1972; Checkland, 1981). This has important consequences not only for analysis but for agricultural policy and planning. It implies that agricultural development cannot be based solely, or largely, on genetic engineering, or macro-economic policy, or even on farming systems research. Each level in the agroecosystem hierarchy has to be analysed and developed both in its own right and in relation to the other levels above and below, and this totality of understanding used as the basis of development. To achieve this is a difficult task but is greatly helped by a common approach to analysis and, in particular, a set of well defined common properties for each level in the hierarchy that can be related to each other, within and between levels.

AGROECOSYSTEM PROPERTIES

Individual organisms can be characterised by the basic properties of growth and reproduction, maintenance and survival (Table 1). In cybernetic terms the 'goal' of an organism is increased fitness and this is achieved through one of a variety of combinations of high and low values of these properties. The particular combination present in an organism can be regarded as its life

TABLE 1 The Properties of Ecological Systems (Conway, 1982b)

Individual Population Community Ecosystem Agroecosystem

Fitness (Fitness) - - - - Social value Growth Productivity Productivity Reproduction Stability Stability Maintenance Resilience Sustainability Survival Equitability

'Goal' System

properties

100 Gordon R. Conway

history strategy (MacArthur & Wilson, 1967; Grime, 1979). For natural populations, communities and ecosystems it is possible to define a similar set of system properties, consisting of (1) productivity, (2) stability (constancy) and (3) resilience (as defined by HoUing, 1973). In each case these refer to the numbers or biomass of individuals or species, or some combination of these measures. Unlike individual organisms, though, there is no obvious 'goal' for a population, community or ecosystem and these properties are simply the outcomes of co-evolution.

However, for agroecosystems a clear goal, in the form of increased social value, is once again apparent. Social value, defined here in terms consistent with classical welfare economics (see, for example, Layard & Waiters, 1978), is a function of the amounts of goods and services produced by the agroecosystem, their relationship to human needs (or happiness) and their allocation among the human population. Like fitness, it has a time dimension, humans seeking not only increased benefits in the immediate future but also a degree of security over the longer term. Social value thus has several measureable components: the present production, its likely level over a future time horizon and its distribution among the human population. Each agroecosystem, at each level in the hierarchy, has a social value and it also follows that one form of agroecosystem may have a greater social value than another (in much the same way that one organism is fitter than another) and hence may be selected for by a human population.

While welfare economics provides a good theoretical basis for defining social value, the concepts involved are of limited practical value. Production frontiers, utility and welfare functions are difficult, if not impossible, to measure. In practice, therefore, an assessment of an agroecosystem's performance has to be made not in terms of the theoretical goal but in relation to those key system properties that contribute most directly to realising the goal. I have suggested there are four such primary agroecosystem properties--productivity, stability, sustainability and equitability (Conway, 1982a,b). The first three approximately correspond to the properties of natural ecological systems; the principal distinction is that each is defined in terms of the valued output of the system and hence may be measured in both biological and socio-economic units (Altieri & Anderson, 1986). The fourth property, equitability, has no direct counterpart in natural ecological systems.

Productivity

Productivity is defined here as the output of valued product per unit of resource input. Common measures of productivity are yield or income per hectare, or total production of goods and services per household or nation,

The properties of agroecosystems 1 O1

but a large number of different measures are possible, depending on the nature of the product and of the resources being considered. Yield may be in terms of kilograms of grain, tubers, leaves or of meat or fish or any other consumable or marketable product. Alternatively, it may be converted to value in calories, proteins or vitamins or to its monetary value at the market. Frequently, the valued product may not be yield in conventional agricultural terms. It may be employment generation, or an item of amenity or aesthetic value or one of a wide range of products that contribute, in ways that are difficult to measure, to social, psychological and spiritual wellbeing (Chambers, 1986).

The three basic resource inputs are land, labour and capital. Strictly speaking, energy is subsumed under land (solar energy), labour (human energy) and capital (fossil fuel energy). Similarly, technological inputs, such as fertilisers and pesticides, are components of capital, but both energy and technology can be treated, for many purposes, as separate inputs.

Each possible combination of output and input can be regarded also as measures of efficiency of production when two or more agroecosystems are compared (NAS, 1975; Spedding, 1979). Assessments may be made of productivity at different levels in the hierarchy of agroecosystems, of the field, farm, village, watershed, region or nation. Also comparisons may be made between agroecosystems of different types (e.g. between a cornfield and a cottonfield, or a lowland and an upland village). Over time productivity may rise, fall or remain static.

Stability

Stability may be defined as the constancy of productivity in the face of small disturbing forces arising from the normal fluctuations and cycles in the surrounding environment. Included in the environment are those physical, biological, social and economic variables that lie outside the agroecosystem under consideration. The fluctuations, for example, may be in the climate or in the market demand for agricultural products. Productivity may be defined in any of the ways described above and its stability measured by, say, the coefficient of variation in productivity, determined from a time series of productivity measurements. Since productivity may be level, rising or falling, stability will refer to the variability about a trend.

Sustainability

Sustainability is defined as the ability of an agroecosystem to maintain productivity when subject to a major disturbing force. The actual or potential disturbance may be caused by an intensive stress, where stress is defined as a frequent, sometimes continuous, relatively small and


predictable disturbing force which has a large cumulative effect. Salinity, toxicity, erosion, indebtedness or declining marketdemand are examples of such forces. Alternatively, the disturbance may be caused by a shock, defined here as an infrequent, relatively large and unpredictable disturbing force which has the potential of creating an immediate, large disturbance or perturbation. Examples of shocks include a rare drought or flood, or a new pest or the sudden rise in an input price, such as that of oil in the mid 1970s.

Following a stress or shock the productivity of the agroecosystem may be unaffected, or may fall and then return to the previous level or trend, or settle to a new lower, or sometimes higher, level or may disappear altogether. Various measures of sustainability are available: they include the inertia (resistance), elasticity, amplitude, hysteresis and malleability of the agroecosystem in response to a disturbing force (Orians, 1975; Westman, 1978). Sustainability thus determines the persistence or durability of an agroecosystem's productivity under known or possible conditions. It is a function of the intrinsic characteristics of the agroecosystem, of the nature and strength of the stresses and shocks to which it is subject, and of the human inputs that may be introduced to counter these stresses and shocks.

A ubiquitous input is the subsidy, often in the form of a fertiliser application, intended to counter the stress of repeated harvesting. Sustainability is maintained only by renewed fertiliser application. Another common form of input is a control agent; for example, a pesticide to counter pest or disease attack. Again, sustainability may necessitate repeated pesticide applications, but an alternative strategy may be the introduction of a biological control agent, such as a parasitic wasp, which may so permanently alter the intrinsic sustainability characteristics of the agroecosystem as to obviate the need for further intervention. In some situations inputs may become part of the problem because, directly or indirectly, they generate stresses and shocks. Frequent pesticide applications, for example, may elicit pesticide resistance and hence growing pest attack. The number of applications may have to be increased to sustain productivity, but in the end productivity may still collapse (Fig. 3).

Equitability

Equitability is defined as the evenness of distribution of the productivity of the agroecosystem among the human beneficiaries. Once again, the productivity may be measured in many ways, but, commonly, equitability will refer to the distribution of the total production of goods and services of the agroecosystem under consideration, i.e. the field, farm, village or nation. The human beneficiaries may be the farm household, or the members of a village or a national population.


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Equitability may be measured by a Lorenz curve, Gini coefficient or some other related index (Lorenz, 1905; Gini, 1912; Kuznets, 1955; Theil, 1967; Atkinson, 1970, 1975; Gastwirth, 1972; Sen, 1973, 1976; Fields, 1980; Kakwani, 1980). In practice, though, it is difficult to define equitability in a purely positive sense, the measures available reflecting different value judgements. Equitability is thus often the evenness of distribution of productivity among the human beneficiaries according to need.

FACTORS AFFECTING SYSTEM PROPERTIES

Although the four properties, described above, are the key properties in determining the social value of an agroecosystem there are a large number of other ways that can be used to characterise an agroecosystem. Examples


include energy and materials conservation, diversity, autonomy, market penetration and some measure of cultural acceptability. Each of these, however, can be shown to contribute to social value through one or more of the four primary properties, in much the same way as birth rate contributes to the productivity o f a population or photosynthesis to the growth of a plant. Thus materials conservation can contribute to productivity but also has a major effect on stability and sustainability; diversity contributes to all four primary properties, al though in rather complex ways; and cultural acceptability is an important component of sustainability and equitability.

An early step in the analysis of a given agroecosystem is to identify the important factors and processes that affect the primary system properties. Table 2 shows one such list for the high altitude villages in the Karakoram mountains of nor thern Pakistan, produced during an Agroecosystem Analysis workshop (Conway et al., 1985).

TABLE 2 Key Variables and Processes Affecting the System Properties of Villages in the Northern

Areas of Pakistan (after Conway et al., 1985)

Positive Negative

PRODUCTIVITY Construction of Karakoram Highway Development of new land Inorganic fertilisers New wheat and fruit varieties Introduction of seed potato cultivation New credit loan system

STABILITY Integration of crops and livestock Co-operative marketing Improvement of irrigation channels

SUSTAINABILITY Farmyard manure Crop rotation (wheat, potatoes) Training of village livestock specialists

EQUITABILITY Traditional co-operation Creation of Village Organisations Rotation of pasturing Development of new land

Shortage of cultivable land Shortage of water Weeds, pests and diseases Seasonal labour shortage

Crop pests and diseases Livestock diseases Temperature fluctuations

Glacier movement Mudflows, avalanches Earthquakes River bank erosion Virus of seed potatoes Overuse of pesticides

Sale of land Education Emigrant labour


AGRICULTURAL DEVELOPMENT

The four properties are linked with each other, both within an agroecosystem and between agroecosystems at different levels in the hierarchy. However, the linkages are complex and frequently negative in effect. If we now regard the properties as normative indicators of performance, rather than neutral descriptors, then agricultural development will involve significant trade-offs between them. For example, a large-scale irrigation project may achieve greater overall productivity yet be at the expense of sustainability and equitability. Similarly, too much emphasis on equitability may inhibit productivity. Within a farm, high stability and sustainability may depend on a complementary diversity of crop fields and livestock systems, each of which produces less than its maximal potential and is more variable in yield and individually less sustainable than is the total farm. A similar situation can occur between the nation and its agricultural regions.

The trade-offs can be seen clearly in the history of agriculture. Each combination of properties can be thought of as an agroecosystem strategy, successive phases of agricultural development reflecting different priorities and hence strategies. The following selected examples from agricultural history are intended to illustrate these points.

The origins of agriculture

Much is known about the where, when, and, to some extent, how, of the origins of agriculture, but there is still considerable controversy over the why (Reed, 1969; Higgs & Jarman, 1972; Bender, 1975; Clark, 1976; Cohen, 1977; Orme, 1977). It is generally accepted that agriculture, by which I mean the cultivation or husbandry of domesticated plants and animals, began independently in at least six widely dispersed regions of the world--the Fertile Crescent (c. 9500BP), Mesoamerica (c. 7000 BP), South America (c. 6000BP), Southwest China (c. 7000BP) and Southeast Asia (c. 6000BP), and Northern India (c. 8500BP). The difficult question to answer is why such a revolutionary event should have occurred in such widely dispersed places, at roughly the same time.

A number of cultural explanations have been proffered (Braidwood & Howe, 1960; Braidwood & Willey, 1962; Ucko & Dimbleby, 1969) as have hypotheses which suggest agriculture was a response to the pressures of an adverse period of climate (Childe, 1936) or of population growth (Cohen, 1977). In each case the writers have assumed, explicitly or implicitly, that the crucial advantage of agriculture over hunting and gathering was its greater productivity. However, a number of arguments suggest that, at least initially, it may have been the relative stability of agriculture that was more important.


Hunter-gathering can be highly productive: the Pacific Coast Indians of North America, for example, were able to support themselves at much higher densities than agricultural groups elsewhere in the Continent (Kroeber, 1939; Baumhoff, 1963). But the basic hunter-gatherer foods-- migratory salmon, acorns, wild cereals--usually show dramatic year to year fluctuations. Moreover, many of the centres of origin exhibit highly seasonal and variable climates and are characterised by mosaics of 'good' and 'bad' food-producing environments. Significantly, the archaeological evidence reveals that, at least in the Fertile Crescent and Mesoamerica, agriculture remained a minor contribution to food supply for long after its inception, 4000 years in the case of Mesoamerica (Flannery, 1969; Bray, 1977). As Boserup (1965) suggests, agriculture may have begun by small daughter bands migrating, in response to local population pressure, into areas more marginal for the wild staple crops. Here the yields were likely to have been even less stable and cultivation and domestication may have arisen as a response to this pronounced instability.

Once, however, agriculture began to spread into other regions of the world, particularly to temperate climates, its superiority in productivity terms was clearly apparent and it was rapidly adopted (Clark, 1965; Ammerman & Cavalli-Sforza, 1971). There were consequences, though, for sustainability and equitability. Early irrigation bought stresses from rising water tables and salinity; grain yields in Sumer dropped from 1850kg/ha to 650kg/ha between 2400 BC and 1700 BC (Jacobsen & Adams, 1958) and there is archaeological evidence of erosion turning arable to wasteland (Dennell & Webley, 1975). Equitability, too, may have declined wherever agriculture became associated with family ownership of land.

Manorial agriculture

One of the longest lasting agroecosystems in history was the manorial system, introduced into Britain by the Anglo-Saxons in the 7th Century and persisting until the 14th century (Aston, 1981). Although considerable differences arose from place to place the essential features of the system remained remarkably constant (Gras, 1925; Ernle, 1961; Stenton, 1965; Baker, 1983). The ecological basis of its sustainability was the three course rotation of the open fields (two course on poorer land, Gray, 1915), that followed a sequence of winter wheat or rye, spring sown oats, barley, beans or other legumes and then a ploughed fallow. This helped prevent the build up of pests, diseases and weeds, while marling and a limited use of manure ensured a good soil structure. Sustainability was promoted also by the strict control enforced by the village council over cultivation dates, stocking rates and the allocation of land (Ault, 1965).


Despite the hierarchy of the feudal system there appears to have been a relatively high degree of equitability, at least among the landholding peasants. The individual strips in the open fields were allocated so that each family received a fair share of good and bad land while grazing rights on the open fields and on the commons were equally shared.

Productivity, though, was low. Cereal yields were little changed from those of the wild harvests several thousand years before in the Fertile Crescent (Harlan, 1967). Returns to seed were only three- to six-fold. Oats and barley gave the highest yields per acre but the return on the seed sown was lower than that of wheat. A good idea of the stability of production can be obtained from a remarkable set of manorial records (Fig. 4). Oats were the most stable crop and this may explain why it was the mainstay of the peasant's food. Note that in the very wet years of 1315-1317 wheat yields were greatly reduced while oats were little affected. Pretty (1981) has analysed the responses of these crops to disturbance and shown that oat yields recovered more quickly than wheat following a bad year. Oats were also more stable in terms of price.

Eventually, the manorial system did break down, partly under the pressure of growing population. By the early 14th century productivity was falling, to the extent that some land was being abandoned (Titow, 1969). Other contributing factors were the growth of a monetary economy replacing that based on allegiances and barter, and the pressure for social change. The process was also accelerated by the outbreak of plague, known as the Black Death, which entered Britain in 1348.

The collapse of the manorial system and the enclosure of the open fields to produce individual estates and farms caused great hardship among the peasantry but increased productivity per unit of land and labour. Moreover, it made possible the application of the 18th century scientific revolution associated with the names of Townshend, Coke, Bakewell, Tull and others, which managed to combine high productivity with sustainability based on rotations incorporating roots and legumes and intensive recycling of crop and livestock waste (Plumb, 1952; Kerridge, 1955; Parker, 1955; Riches, 1967; Chorley, 1981).

Modern western agriculture

The dominant factor in western agriculture during the latter part of the 20th century has been protectionism. In the UK, for example, the experiences of the great agricultural depressions, notably at the end of the 19th century and in the 1930s, led to the passing of the Agricultural Act of 1947 which introduced a wide range of subsidies and guaranteed prices for most major agricultural products. Subsequently, the creation of the Common


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Agricultural Policy in 1957 under the European Economic Commission (EEC) instituted the right to comparability of income between workers in the agricultural and industrial sectors throughout most western European countries and ensured this through a complicated system of external tariff walls, levies, intervention prices and export refunds. European farmers have been protected from the fluctuations in world markets and productivity has risen dramatically. Over the past three decades nitrogen fertiliser applications in the UK have risen from 200 000 to over 1 400 000 tonnes, and cereal yields from an average 3 tons/ha to 6 tons/ha while the number of farm workers has declined from 800 000 to under 400 000 (Conway, 1984). Large EEC surpluses, notably of beef, milk, cereals, sugar and wine, have been created.

Over the same period land prices have risen and farmers' incomes in Britain doubled, improving in relation to manual and farm workers, whereas other comparable occupations have declined (Bowers & Cheshire, 1983). Although small and marginal farmers have benefited from the subsidies, the bigger, richer and more specialised farmers have benefited more. For the UK as a whole, the CAP system of price guarantees is effectively borne by the public as consumers, rather than as taxpayers, and hence the impact on income distribution has been regressive.

The increased agricultural productivity has also been at the expense of the amenity, recreation and conservation values of the countryside. There have been recent, large-scale losses of ancient woodlands, chalk grasslands, herb rich meadows, heaths, hedgerows, lakes, fens and mires (Nature Conserv- ancy Council, 1984). Moreover, this has occurred at a time when use of the countryside for walking, angling, camping, horseriding, and natural history pursuits involves millions of the public and is rising dramatically (Conway, 1984). Pollution from agriculture is also increasing. Water pollution incidents arising from livestock or silage effluent have doubled since 1979 in the UK (WAA, 1986), while in several parts of the country nitrate levels in drinking water supplies are close to new European limits (Young et al., 1976; Oakes, 1981; Wilkinson & Greene, 1982). In these cases the costs of pollution caused by agriculture are borne by the public rather than by the farming community.

How sustainable is this high level of production remains open to debate. There is some evidence for increased soil erosion (Morgan, 1985a,b) and concern is being expressed over soil quality and the danger of growing pesticide resistance. More important, however, is the cost of subsidising production at the present levels. Western European governments have already instituted milk quotas and are examining the various consequences of moving toward a lower input/lower output agriculture.

In North America protection generally has been at a somewhat lower

1 l0 Gordon R. Conway

level. Indeed, part of the cause of current high levels of bankruptcies among US farmers is lack of protection from fluctuating world prices. Average yields per hectare for cereals are generally lower than in Europe (2 tons/ha is the national average for wheat in the USA compared to 6 tons/ha in the UK). Nevertheless, there have been dramatic increases in productivity, particularly in returns to labour, resulting from intensive mechanisation and inputs of agrochemicals. But soil erosion is now a major threat and in some regions sustainability is being jeopardised by exhaustion of irrigation water supplies (Crosson & Brubaker, 1982; Larson et al., 1983; Brown & Wolf, 1984; Helms & Flader, 1985; Postel, 1984, 1985).

The Green Revolution in Indonesia

My final example concerns the transformation that has occurred over the last three decades in the agriculture of many of the less developed countries (LDC). Agricultural scientists tend to dislike the phrase 'Green Revolution' with its journalistic overtones. But the exploitation of the new cereal varieties, bred by the International Agricultural Research Centres, with their high pay-off genetic characteristics of resistance to lodging, insensitivity to photoperiod and early maturation, coupled with the organisation and distribution of high pay-off inputs such as fertilisers, water-regulation and pesticides, and targetted on the best favoured agroclimatic regions and the most progressive farmers, has all the hallmarks of a successful technological revolution.

The benefits in terms of productivity have been very great. Over the past two decades food production in Asia has grown overall by 15% per capita and many countries in the region are close to cereal grain self-sufficiency. Indonesia's rice production has grown from under 14 million tons in the late 1960s to over 25 million tons in 1984 and the country now has a small surplus.

This dramatic increase in LDC productivity has been accompanied, however, by numerous problems, ranging from pest and disease outbreaks to loss of communal self-help arrangements (Grabowski, 1951; Frankel, 1971; Cleaver, 1972; McNeil, 1972; Nickel, 1973; Collier et al., 1974; Griffin, 1974; Hauri, 1974; Palmer, 1976; Collier, 1977; IRRI, 1979, 1980, 1981; Murdoch, 1980; Pearse, 1980; Hayami, 1981; Maunder & Ohkawa, 1983; KEPAS, 1984). In Indonesia the rice production strategy received a severe setback in the mid-1970s due to recurring and devastating outbreaks of brown planthopper (Nilaparvata lugens) (Conway & McCauley, 1983). A switch to a new variety, IR36, was followed by a serious attack of tungro disease, necessitating yet new varietal introductions. Large-scale plantings of uniform crop varieties are intrinsically prone to pest and disease build up,


particularly where planting is asynchronous (Loevinsohn, 1984). Sustain- ability in these circumstances is dependent on the crop breeders always staying one step ahead.

Indonesia's rice strategy has also had dramatic effects on labour use and equitability (Conway & McCauley, 1983). Prior to the introduction of the new rice varieties the harvest was open to all members of the village, the poor and landless being able to retain a fixed proportion of the rice they harvested. But the growing number of landless has made it difficult for farmers to control the harvesting so that now it is carried out by contract groups (Collier et al., 1973). The traditional hand-milling of rice by the women of the village, who received grain in lieu of money payment, has also disappeared, replaced by mechanical hulling (Timmer, 1973). And, despite self-sufficiency, malnutrition persists, even in some of the most agriculturally productive villages.

The final question is whether the national effort is sustainable. Indonesia's oil and gas boom is now over and the budget surpluses which subsidised the agricultural revolution are gone. Inevitably, there will be bad years due to pest and disease outbreaks or poor rainfall. These will place a heavy demand on central resources and agencies who will have to deliver what in the past was the function of communal self-help arrangements and the evolved diversity of traditional agroecosystems.

AGROECOSYSTEM ANALYSIS AND DEVELOPMENT (AAD)

Until recently the various agricultural regions of the world differed from each other in the various weights accorded the agroecosystem properties. In the 1930s, for example, conservation agriculture was being practised in Britain while the Dust Bowl was being created in the midwest of the USA. But today agriculture is facing a common worldwide challenge. The pursuit of high productivity in both the developed and less developed countries has brought with it declines in sustainability and equitability that increasingly are being regarded as undesirable. Our present priority is for policy research, practical analytical tools and development packages aimed at increasing agricultural sustainability and rectifying undesirable inequities.

One step in this direction has been the development of Agroecosystem Analysis (Conway, 1985a, 1986). This is a technique of multidisciplinary analysis which may be used at any level in the agroecosystem hierarchy, and generates a set of research and development priorities that explicitly take account of the trade-offs between the system properties. The technique has been used so far to determine research priorities for university and government teams (Gypmantasiri et al., 1980; KKU-Ford, 1982a,b; KEPAS


1985a,b), development priorities in project design (Limpinuntana & Patanothai, 1984; Conway et al., 1985) and to evaluate project performance and recommend corrective actions (Conway & Sajise, 1986).

A second component ofAAD (Conway, 1985b) is the further development and refinement of a variety of packages that promise high productivity without loss of sustainability or equitability. Such packages include integrated pest management, multiple cropping, crop livestock polyculture, agroforestry, communal resource use, communal water control, social forestry and integrated handcraft manufacture.

The next step is to devise ways of incorporating these concepts, tools and packages into formal policy and project design in such a way that the trade- offs are made explicit and accounted for in as rigorous a manner as is currently customary for conventional economic analysis.

ACKNOWLEDGEMENTS

I am grateful for helpful comments from Richard Morris, lain Craig, Tariq Husain and Richard Sandbrook. I was ably assisted in the research by Jules Pretty. The work was carried out under a grant from the Rockefeller Brothers Fund.

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