1 Soil Acidification and Alkalinization.- 1 Introduction.- 2 Definitions.- 3 Effects of Addition of Dissolved Strong Acid or Base.- 4 Internal Acid Production in Soils.- 5 Assimilation of Minerals by Biota.- 6 Redox Processes.- 7 Order of Magnitude of ?ANC by Various Groups of Processes.- References.- 2 Proton Sinks in Soil Controlling Soil Acidification.- 1 Introduction.- 2 Survey of Proton Sinks in Soil.- 3 Adsorption of Protons by Soil Constituents.- 4 Proton Consuming Dissolution Reactions.- 5 Secondary Reactions.- 5.1 Influence of Clay Minerals on Al-Speciation and Protonation of AlOH-Groups.- 5.2 Al-Saturation and pH Buffer Capacity of Clay Minerals.- References.- 3 An Ecosystem Approach to Soil Acidification.- 1 Implications of the Material Balance of the Ecosystem for Soil Acidification.- 2 Ecosystem Environment and Ecosystem Compartments.- 3 Can Ecosystem Theory be Based on Thermodynamic Laws?.- 4 A Mathematical Model of Terrestrial Ecosystems.- 5 Definitions of Acids and Bases in Soil.- 6 Inputs of Acids and Bases into Ecosystems.- 7 Input/Output Relations.- 8 Calculation of Proton Balances.- 9 State Variables of the Acid/Base Status of the Ecosystem.- 10 Assessment of Changes in Soil Acidity.- 11 The Temporal and Spatial Pattern of Soil Acidity.- 12 Interrelationship Between Ecosystem Functioning, Changes in Acid/Base Status of Soil, and Soil Development.- References.- 4 Influence of the Acid/Base Status on the Formation and Interactions of Acids and Bases in Soils.- 1 Introduction.- 2 Small Organic Acids in Soils.- 3 Macromolecular Acids in Soils.- 4 Organic Bases in Soils.- 5 Influences of Organic Acids and Bases in Soils.- 6 Summary and Conclusions.- References.- 5 The Chemistry of Aluminium, Iron and Manganese Oxides in Acid Soils.- 1 Introduction.- 2Aluminium Oxides.- 3 Iron Oxides.- 4 Manganese Oxides.- References.- 6 Assessing the Solubilities and Reaction Kinetics of Aluminous Minerals in Soils.- 1 Introduction.- 2 Experimental Determination of the Stabilities of Aluminous Minerals.- 3 Kinetics of Aluminous Mineral Precipitation/Dissolution Reactions.- 4 Interaction of Aluminous Mineral Stabilities and Reaction Kinetics in Soils and Other Terrestrial Systems.- References.- 7 Nutrient Status and Toxicity Problems in Acid Soils.- 1 Introduction.- 2 Soil Acidity and Nutrient Status.- 3 Toxicity Problems in Acid Soils.- 4 Ion Activities in the Soil Solution: An Alternative Perspective to Soil Acidity Problems.- 5 Concluding Remarks.- References.- 8 Effects of Soil Acidity on Plant Associations.- 1 Introduction.- 2 Effects of Single Factors.- 3 Interactions.- 4 Conclusions.- References.- 9 The Transfer of Acidity from Soils to Surface Waters.- 1 Introduction.- 2 Acid Neutralizing Capacity in Water.- 3 Acid Neutralizing Capacity in Soil Solutions.- 4 Quantification of the Processes.- 5 Other Processes.- 6 Conclusions.- References.