|Environment, Biodiversity and Agricultural Change in West Africa (UNU, 1997, 141 pages)|
|4: Criteria for designing sustainable farming systems in tropical Africa|
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|
|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:
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:
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).