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4: Criteria for designing sustainable farming systems in tropical Africa

Sustainable agriculture
Farming systems of tropical Africa and their sustainability under changing conditions
Ingredients of sustainable farming systems and issues to be considered in the design of these systems
Sectorial interface requirements
Conclusions and recommendations

Bede N. Okigbo

The World Commission on Environment and Development (WCED 1987) defined sustainable development as development that meets the needs of the present without compromising the ability of future generations to meet their own needs. Although I do not feel like adding to the unending list of definitions of sustainable development, there is need to consider definitions that make it easier to better conceptualize the nature and processes involved in sustainable development rather than the usual listing of characteristics of the term(s). Here, I attempt to present an operationally practical definition of sustainable development as the current global development paradigm consisting of policies, plans, programmes and activities of conserving, managing and utilizing resources to at least satisfy basic needs and improve human welfare by employing such strategies, technologies, processes and systems of production that do not degrade the resource base, cause losses or changes in the environment that are ecologically, economically and culturally undesirable. According to the WCED (1987) definition, the changes that are ecologically, economically and culturally undesirable are those that damage the environment to the extent that future generations will find it more difficult to find ways or generate technologies for rehabilitating the degraded environment and/or reversing the adverse changes in order to utilize environmental resources to meet their needs and ensure human welfare than we are finding it easy today to achieve the same objective. In other words, sustainable development consists of practices and techniques of managing and utilizing resources to fulfil human needs without damaging the environment so badly as to make it more difficult for future generations to manage and utilize environmental resources to satisfy their own needs.

Sustainable agriculture

Sustainable agriculture has been variously defined as follows:


According to Dover and Talbot (1987), although sustainability means different things to different people, on the basis of ecological principles sus tainable agricultural systems are those whose productivity can continue indefinitely without undue degradation of other ecosystems.

  1. According to SCA (1991), sustainable agriculture is the use of farming practices and systems which maintain or enhance:
  1. A system synonymous with alternative agriculture, which is any system of food or fibre production that systematically pursues the following goals:

These agricultural systems employ a broad spectrum of practices that include:

In this paper, for a discussion on criteria for designing sustainable agricultural systems, I hope you will bear with me for introducing yet another definition. Sustainable agriculture is the science, art and business enterprise in which the farmer manipulates environmental resources and orchestrates several inputs in amounts, quality, sequences and timing in order to bring about or "create" environmental conditions that favour the production of plant and/ or animal products needed for food, fibre and other products without causing environmental degradation and decline in yields. Sustainable agriculture in any given location can only be achieved where there is appropriate scope of research linked with extension and the farmer to ensure that there is knowledge, skill, understanding and technology for manipulating and dealing with:

In a sustainable farming system, despite the vicissitudes of the weather, climate, political and socio-economic conditions causing perturbations in the yield curve, the overall trend does not show a decline in the long term. This paper is devoted to a review of the main characteristics of the farming systems of tropical Africa, extent of their sustainability, changes they are undergoing under impacts of different human activities and a host of other factors, reasons why they are becoming unsustainable and what needs to be done to render them more sustainable now and in the future. Finally, based on an understanding of the causes of unsustainability of the existing farming systems, the ingredients that must be wrought into farming systems during the design stage are considered.

Farming systems of tropical Africa and their sustainability under changing conditions

Farming systems in tropical Africa consist of an amalgam of crops and animals managed in various production systems with their component cultural practices and technologies made up of varying mixes of traditional and introduced elements adapted to the requirements of different ecological zones and peoples of diverse cultures. As in other parts of the world, these systems are culminations of several millennia of experimentation which gave rise to extensive production systems such as shifting cultivation and nomadic herding - sustainable systems that were economically viable, ecologically sound and culturally acceptable under the then prevailing low population densities. With increasing population pressure these gave rise to more intensive fallow systems. The various characteristics of these farming systems are listed below:

The various farming systems consist broadly of traditional (e.g. bush fallow and compound farms) systems, transitional systems (e.g. smallholder cocoa and coffee plantations) and modern farming systems and their local adaptations, such as large-scale plantations, ranches, poultry farming and market gardening. The details of these typologies need not concern us here. What is of concern is that the farming systems are not static. They are changing as a result of changes in the environment, both natural and socio-economic. Some of these changes have rendered the traditional farming systems unsustainable and somewhat outmoded. A few examples of the changes and their effects on sustainability are presented hereunder:

Change Effect on Sustainability
Introduction of Asian and American crops Positive and negative
Population explosion Negative
Commercialization of agriculture Largely negative for low resource farmers
Mechanization Largely negative, sometimes positive
Agricultural chemicals Largely negative unless strictly controlled
Fertilizer use Negative and positive
European settlement Negative and positive

The manner in which changes affect sustainability can be illustrated with two or more of these examples. For instance, the introduction of Asian and American crops can be regarded as contributing to the increase of biodiversity and therefore contributing to increasing stability of production and biodiversity. But it is also true that the production of the introduced crops has often been promoted at the expense of the indigenous food crops, some of which are so neglected that they are not much being grown and a considerable degree of biodiversity has been lost. Population explosion has considerably increased pressures on land, resulting in intensification of farming associated with a drastic shortening of the period of fallowing from about 10 years or more to only 2 years or less. Use of agricultural chemicals has different impacts on the environment. Where reasonable amounts of chemicals are appropriately used, the effects are largely beneficial. Where, for example, no fertilizers are used and farming is intensified, the nutrients are depleted and yields drop as soils become degraded. But where excess amounts of farm chemicals are applied the environment may become polluted and unsustainability is the result.

Causes of Unsustainability in Agriculture of Developing Countries in Africa

The intensification of agricultural production as a result of increasing population pressure, intensification of farming, overgrazing and conversion of land to several uses that were not tested in the evolution of farming systems in Africa, have resulted in several undesirable changes in the environment with adverse effects on agricultural production. Figure 4.1 shows that with intensification of farming due to population and other pressures the following changes occur:

Figure 4.1a Why and How Certain Systems Become Non-viable (Source: FAO 1991a)


Figure 4.1b Why and How Certain Systems Become Non-viable (Source: FAO 1991a)


Table 4.1 Inputs of Technologies Used in Traditional and "Modern" Conventional Farming Systems

  Traditional agriculture Modern agriculture
Land Small (<1-5 ha) Large (10-100 ha or more)
Tools Simple: fire, axe, hoe, digging sticks, machete Complex: tractors and imple meets, threshers, combine harvesters, etc.
Crops Many species (5-80), land races, no genetic improvement, wide genetic base Few species (1-3), improved narrow genetic base
Animals Several species (2-5) Usually 1 or 2 species
Labour Manual, human energy, or animal power Mechanical, petroleum fuels, electrical energy
Soil fertility maintenance Fallows, ash, organic manures Inorganic fertilizers, sometimes manures, soil amendments, e.g. lime and gypsum
Weed control Manual, cultural Mechanical, chemicals (herbicides and petroleum-based products)
Pest and disease management Physical/cultural Mainly mechanical, chemicals, insecticides, fungicides, bactericides, nematocides, rodenticides
Crop management Manual Growth regulators for defoliation, control of flowering, fruit drop, etc.
Harvesting Manual or with simple tools Mechanical, tractors plus implements: pickers, balers, threshers, combine harvesters
Post-harvest handling and drying Simple sun-drying and over fires Mechanical forced-air artificial drying using petroleum fuels, sometimes refrigeration

Source: Okigbo (1988).


The changes that take place under intensive agriculture are the same as those that occur under shifting cultivation except that the inputs used vary.

Table 4.1 shows the differences in practices and inputs used in traditional agri culture as compared to those used in "modern" intensive agriculture. Note that while simple hand tools used in traditional agriculture do not cause compaction, heavy machinery used in intensive agriculture does and this, in turn, causes structural deterioration, poor drainage and waterlogging.

Case-study of Changes Causing Environmental Degradation and Reduced Productivity in Southern Nigeria

Lal and Okigbo (1990) conducted an assessment of soil degradation in the southern states of Nigeria and identified factors that cause environmental degradation in the humid tropics of southern Nigeria and in the humid tropical African environment.

The main change in traditional farming systems is that of intensification of farming and the shortening of the periods of fallow. It was found that changes that occur in the soil are physical, chemical and biological, and there were changes of a socio-economic character also. If these changes are identified, it is possible for us to incorporate into the production system practices, technologies, etc., which will prevent adverse changes that threaten sustainability.

The main causes of soil degradation encountered were:

The most serious soil degradation occurred in areas where fallow periods are minimal or non-existent. But the effects of long periods of cultivation often result from various practices ranging from clearing and cultivation to subsequent cropping. Symptoms of soil degradation observed were:




Yield Reduction

Commodities and Production System Changes

Sustainable Farming Systems

The assessment of soil degradation in southern Nigeria also resulted in identification of the following as the main sustainable farming systems currently practiced or emerging:

It is obvious from the above that many of the traditional and arable crop farms, especially those that are highly commercialized and on which most of our fertilizers are used, are not sustainable. It is on the basis of the above considerations that the elements of sustainable farming systems to be considered in designing sustainable farming systems will be based in addition to issues discussed in SCA (1991) and Lal and Okigbo (1990).

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