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close this bookEnvironment, Biodiversity and Agricultural Change in West Africa (UNU, 1997, 141 pages)
close this folderThe context
close this folder4: Criteria for designing sustainable farming systems in tropical Africa
View the document(introduction...)
View the documentSustainable agriculture
View the documentFarming systems of tropical Africa and their sustainability under changing conditions
View the documentIngredients of sustainable farming systems and issues to be considered in the design of these systems
View the documentSectorial interface requirements
View the documentConclusions and recommendations
View the documentReferences

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:

  • small farm size with over 80 per cent of the farms between 0 and 5 ha;
  • farming predominantly for subsistence but increasingly becoming commercial with from less than 10 per cent to over 90 per cent of produce offered for sale in local markets or for export;
  • widespread reliance on simple tools and manual labour with minimal use of animals and/or machinery for work;
  • marked division of labour between the sexes;
  • most farming activities and production systems very closely related to prevailing rainfall regimes;
  • acute labour shortage especially during peak periods of main farm operations such as clearing, planting, weeding, etc.
  • widespread practice of slash and burn clearance systems;
  • widespread reliance on fallowing and nutrient cycling by vegetation for maintenance of soil fertility lost during the cultivation phase or as a result of prolonged and more intensive cultivation;
  • lack of credit and hence limited use of costly inputs such as fertilizers, soil amendments, pesticides, farm machinery, etc., which could significantly increase areas under cultivation and total productivity;
  • in most traditional farming systems crop production may be practiced hand in hand with livestock or animal rearing, but the extent of integration varies from one farm to another and the number and species of animals kept depend on the presence or absence of diseases such as trypanosomiasis;
  • political instability and ethnic strife in some countries, making production impossible or harvesting risky (Okigbo 1985).

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)


  • intensification of land use for food production
  • shortened fallow periods
  • reduced capacity for soil regeneration
  • decline in soil fertility
  • reduced and declining yields
  • food shortages
  • food imports

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


  • use of marginal sloping lands
  • overgrazing and overstocking
  • loss of vegetative cover
  • exposure to wind
  • exposure to rainfall
  • increased surface run-off
  • soil erosion
  • landslides and downstream flooding
  • reduced aquifer
  • water shortages

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).


  • increased fuel needs
  • deforestation
  • unregulated logging
  • loss of fauna and flora habitat
  • extinction of genetic species and loss in biodiversity

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:

  • fire and burning of vegetation especially on roadsides and adjacent areas covered by Siam weed, Chromolaena odorata; deforestation and land clearing;
  • intensification of farming and shortening of fallow periods;
  • low input agriculture - no fertilizers applied to food crops under continuous cultivation;
  • accelerated erosion;
  • construction of roads, buildings and industrial infrastructure.

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:


  • surface seal formation, crusting and compaction of surface horizon;
  • reduction of infiltration rate;
  • reduced water-holding capacity; increased bulk density;
  • increased susceptibility to raindrop impact and soil splash;
  • leaching out of clay and colloidal fraction in the subsoil.


  • acidification resulting from depletion of bases;
  • decline in pH higher in coarse textured soils;
  • increase in exchangeable Al and H;
  • reduction in soil organic matter and organic carbon;
  • reduction in total and available N and P;
  • nutrient depletion culminating in multiple nutrient deficiencies.


  • changes in number and composition of soil fauna and flora;
  • overall decline in soil fauna under cultivation;
  • seasonal migration of fauna from top to subsoil;
  • clearing and burning resulting in a tendency of pests and diseases to increase, especially where no rotation is practiced;
  • deforestation reported to cause decline in populations of parasitic nematodes after clearing;
  • chemicals, herbicides, insecticides which adversely and differentially affect soil fauna;
  • cropping or cultivation which produces differential effects in different situations;
  • cultural practices such as mulching on surface which encourage earthworm activity;
  • changes in weed species and composition related to commodity produced and practices;
  • burning, which may lower earthworm activity.

Yield Reduction

  • this may be regarded as a biological effect of soil degradation;
  • reduction in yield as a result of degradation varies with soil fertility and structure.

Commodities and Production System Changes

  • increase in areas under cassava and decrease in those of maize and yams, which may be more due to cassava being adapted to degraded soils than to people preferring to eat and grow cassava.

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:

  • home gardens or compound farms;
  • planted fallow systems;
  • alley cropping and related agroforestry systems;
  • wetland rice;
  • market gardens and some tree crop plantations.

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).