Fertility of Soils

General 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 Experiments.- 16.2.1 Interpretation.- 16.3 Analytical Criteria of Soil Fertility.- 16.3.1 Acidity.- 16.3.2 Organic Matter.- 17 Year-to-Year Variation in Yield: The Effect of Rainfall and Its Distribution.- 17.1 Crop Yield and Water Balance.- 17.2 Statisfaction of Water Requirement, Duration of Cropping, and Yield Pattern.- 18 Low Intensity Systems - Hand Cultivation.- 18.1 Change in Yields.- 18.2 Changes in Fertilizer Efficiency.- 19 Hand Cultivation with Intensification.- 19.1 Change in Yield.- 19.2 Changes in the Soil.- 20 Systems Using Animal Traction.- 20.1 Changes in Crop Yield.- 20.1.1 Yield Trends and Fertilizer Usage.- 20.1.2 Effect of Combined Use of Fertilizers and Organic Manures on Yield.- 20.2 Change in Soil Properties Under Mechanical Tillage.- 20.2.1 The Effects of Fertilizers and Manures on Soil Acidification.- 20.2.2 Manures, Fertilizers, and Soil Organic Matter Content.- 20.2.3 Erosion, Organic and Nutrient Balance in the Soil.- 21 Summary of Part III: Indications from Long-Term Experiments.- IV Major Processes in the Development of Soil Fertility.- IVA Items in the Organic Matter Balance in the Soil.- 22 Introduction - Soil as a System.- 22.1 The Soil Under Cultivation as a System.- 22.2 Outline of the Soil-Plant System.- 23 Items in the Organic Matter Balance of Cultivated Soils and Their Evolution.- 23.1 The Main Forms of Soil Organic Matter.- 23.2 Processes Within the Organic Matter Compartment.- 23.3 Inputs to and Outputs from the Organic Matter Compartment.- 23.4 The Organic Matter Balance and Plant Production.- 23.5 Items in the Carbon Balance.- 24 Tillage and the Organic Matter Balance of Cultivated Soils.- 24.1 Ploughing and Yield.- 24.2 Ploughing and Biological Activity.- 24.3 Ploughing and the Circulation of Surface Water.- 24.4 Ploughing and the Organic Matter Balance.- 25 Additions of Plant Nutrients and the Organic Matter Balance in the Soil.- 25.1 Nutrients and Yield.- 25.2 Nutrient Application and Root Growth.- 25.3 Nutrients and the Stimulation of Biological Activity.- 25.3.1 Extension of the Rhizosphere.- 25.3.2 Stimulation of Microbiological Activity.- 25.4 Applied Nutrients and Surface Water Economy.- 25.5 Fertilizers and Soil Organic Matter Balance.- 25.6 Mineral and Organic Nitrogen and the Organic Matter Balance of the Soil.- 25.6.1 Results of Pot Experiments.- 25.6.2 Results of Field Experiments.- 25.6.3 Modification of Organic Materials Added to the Soil.- 26 Establishing the Organic Matter Balance in Cultivated Soils.- 26.1 Crop Yield and the Organic Matter Balance of Cultivated Soils.- 26.2 A Quantitative Approach to the Organic Matter Balance.- 26.2.1 Estimation of the Annual Rate of Soil Organic Matter Loss.- 26.2.2 The Effect of Cultural Practice on k.- 26.2.3 Proposal for Calculating the Organic Matter Balance.- 26.3 Critical Values of Soil Organic Matter Content.- 26.3.1 Organic Matter and Structural Stability of the Soil.- 26.3.2 Organic Matter and Biological Activity in Soil.- IVB Items in the Nutrient Balance of the Soil and Their Evolution.- 27 Forms of Mineral Material in the Soil and Their Distribution.- 27.1 Inorganic Compartments in the Soil.- 27.2 Exchange Mechanisms Between the Three Categories of Soil Nutrients.- 27.3 Nutrient Inputs and Outputs in Cultivated Soils.- 27.4 Calculation of the Nutrient Balance.- 28 Measurement of the Items in the Nutrient Balance of the Soil.- 28.1 Nutrient Inputs.- 28.1.1 Nutrients Added in Organic Manures.- 28.2 Nutrient Outputs from the Soil-Plant System.- 28.3 Nutrient Balance and Water Balance.- 29 Calculated Nutrient Balance for Several Systems.- 29.1 Cotton-Cereal Systems.- 29.2 Nutrient Balance in Millet-Groundnut Systems.- 29.3 Groundnuts and the Nitrogen Balance.- 30 Establishing Nutrient Balance Sheets for Cultivated Soil.- 30.1 Balances for Individual Nutrients.- 30.1.1 Nitrogen.- 30.1.2 Calcium and Magnesium - Soil Acidification.- 30.1.3 Potassium.- 30.1.4 Phosphate.- 30.1.5 Sulfur.- 30.2 Critical Nutrient Levels.- 30.3 Deficiency Levels of Soil Nutrients.- 30.4 Diagnosis of Nutrient Deficiency by Plant Analysis.- 31 Summary of Part IV.- 31.1 Organic Matter Balance.- 31.2 Nutrient Balance.- General Conclusions.- 32 Evolution of Soil Fertility in the Savannah Area to the South of the Sahara.- 32.1 Causes of the Decline in the Fertility of Farming Land.- 32.2 Change in the Fertility of Cultivated Fields and Its Causes.- 33 Requirements for the Establishment of Sustainable Agriculture in the Savannah Zone.- 33.1 Fertility: Technical Proposals and Rural Policy.- 33.2 Management of Fertility in Small Farming Areas.- 33.2.1 Management of Fertility Under Nonsaturated Conditions.- 33.2.2 Management of Fertility - Areas Approaching Saturation.- 33.3 Management of Soil Fertility on the Farm.- 33.3.1 The Prime Requirement for Fertility: The Root System.- 33.3.2 Simple Technical Measures.- 33.3.3 Management and the Information on Which It Is Based.- 33.4 The African Savannah - Land of Good Hope.- References.