InhaltsangabeGeneral Introduction.- 1 Scope of the Study.- 1.1 Geography.- 1.2 Agricultural Conditions.- 1.3 Aims of the Study.- 1.4 Procedure.- 1.4.1 Sources of Information.- 1.5 Interpretation.- 1.6 From Scientific Analysis to Technical Advice: Extrapolation.- I Fertility and Agricultural Development.- 2 Definition of Fertility.- 2.1 Introduction.- 2.2 Components of Fertility.- 2.2.1 Climate and the Plant.- 2.2.2 Soil and the Plant.- 2.3 The General Concept of Fertility.- 2.3.1 Production Potential.- 2.3.2 Costs.- 2.3.3 The Risks.- 3 The Farming Environment.- 3.1 Climate.- 3.1.1 Drought.- 3.1.2 Consequences of Climate for Agriculture.- 3.2 Natural Vegetation.- 3.3 Soil Morphology and Pedology.- 3.3.1 Soils on Dune Sands.- 3.3.2 Soils on the Basement Complex and Continental Sediments.- 3.3.3 Possibilities for Cultivation.- 3.4 Physicochemical Properties of the Soils.- 3.4.1 The Organomineral Fraction.- 3.4.2 Surface Activity.- 4 Population and Migration.- 4.1 Low Density of Population.- 4.2 Population Dynamics.- 4.2.1 Population Growth.- 4.2.2 Composition of the Population.- 4.2.3 Migration.- 4.3 Population and Land Use.- 4.3.1 Rural Exodus and Food Aid.- 4.3.2 Increase in Pressure on Available Land.- 5 Agricultural Policy.- 5.1 Increasing Food Shortage.- 5.2 Agricultural Policies Have Not Provided Security for the Farmers.- 5.3 Conclusion.- II Present Fertility Status.- IIA Crop Yields in Recent Times.- 6 National Yield Trends.- 6.1 Introduction.- 6.2 Stagnant Yields.- 6.3 Some Yields on the Increase.- 6.4 Declining Yields.- 7 Yields in Project Areas.- 7.1 Groundnut Areas.- 7.1.1 Two Intensification Projects.- 7.1.2 Millet and Groundnut in Senegal: Yields 1960-1979.- 7.2 The Cotton Growing Areas.- 7.2.1 Yields Tending to Stabilize Following a Large Increase: Northern Ivory Coast.- 7.2.2 Fluctuating Yields Tending to Decline: Upper Casamance, Senegal.- 8 Summary: Moderate Yields Giving Concern for the Future.- IIB The Development of Soils Under Cropping in Practical Farming.- 9 Soil Development Under Traditional Farming.- 9.1 Clearing from Forest.- 9.2 Clearing After Long Grass Fallow.- 9.2.1 Period Under Continuous Cropping.- 9.2.2 Duration of Fallow and Soil Regeneration.- 10 The Effect of Population Growth on the Soil.- 10.1 Population Increase When Land Is Available.- 10.1.1 Without Change in Farming Systems.- 10.1.2 Land Utilization with Change in Cultural Practices.- 10.2 Rural Population Increase in a Confined Space.- 10.2.1 Consequences for Cultivated Soils.- 10.2.2 Rural Population Pressure, Firewood Shortage, and Soil Deterioration.- 10.2.3 Rural Migration and the Environment.- 10.3 Migration into Thinly Populated Country.- 10.3.1 Migration into Populated Rural Areas.- 10.3.2 Migration and Extensification.- 11 Agricultural Intensification and Its Consequences for the Management of Soil Fertility.- 11.1 Cotton Growing.- 11.2 Intensification of Cotton Growing When Land Is Plentiful.- 11.2.1 Introduction of Animal Traction.- 11.2.2 Change in Allocation of Land Between Crops.- 11.2.3 Mechanized Clearing.- 11.2.4 Disturbance to Traditional Farming Systems.- 11.3 Intensification of Cotton Growing When Land Availability Is Limited.- 12 Summary of Part II.- III Experimental Bases of Sustainability.- 13 Sustainable Yields.- 13.1 Agricultural Research and Sustainability.- 13.2 Assessment of Sustainability.- IIIA The Ecological Approach.- 14 Farming and Physical Degradation of the Soil.- 14.1 Overall Effect of Farming on Soil Degradation.- 14.2 Erosion.- 15 Root Development of Crops and Biological Imbalance in Soils.- 15.1 Soils and Crop Rooting.- 15.2 Cropping and Soil Organisms.- 15.2.1 Living Soil Organisms.- 15.2.2 Farming and Change in Soil Microbiological Activity.- 15.2.3 Cropping and the Activity of the Soil Fauna.- 15.3 Conclusion.- IIIB Soil Development and Crop Yield in Permanent Rain-Fed Farming - Long-Term Experiments.- 16 Introduction - The Interpretation of Long-Term Experiments.- 16.1 General Approach.- 16.2 Selection of Ex