Soil Acidity

Processes of acidification or alkalization of soils are treated, taking the qualitative changes in soil chemistry into consideration. Following a theoretical background of ecosystem proton budgets, the application for assessing external and internal acid loads are demonstrated. The chemistry of organic matter and the oxides of aluminum, iron, and manganese are treated in the context of being sources and sinks for acid loads in soils. Special attention is payed to the assessment of solubility and reaction kinetics of aluminous minerals. The formation of toxic elements in soil solution resulting from the solubilization of inorganic oxides as well as aspects of changes in the nutrient status of soils, changes of fertility and processes leading to a transfer of acidity from soils to surface are discussed.

Contenu

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.- 6.1 Deposition of Air Pollutants.- 6.2 The Role of Silicate Weathering.- 7 Input/Output Relations.- 8 Calculation of Proton Balances.- 9 State Variables of the Acid/Base Status of the Ecosystem.- 9.1 Buffer Ranges in Soil.- 9.2 Carbonate and Silicate Buffer Range.- 9.3 Cation Exchange Buffer Range.- 9.4 Aluminum and Iron Buffer Range.- 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.- 12.1 Stable Ecosystems Close to Steady State.- 12.2 The Aggradation Phase.- 12.3 The Phase of Humus Disintegration.- 12.4 The Phase of Buildup of a Decomposer Refuge.- 12.5 The Phase of Podzolization.- 12.6 Krypto-Podzolization.- 12.7 Deacidification.- 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.- 3.1 Humic Substances.- 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.- 2 Aluminium Oxides.- 2.1 Soil Species and Their Solubility.- 2.2 Reactivity of Allophane and Hydroxyaluminium Interlayers.- 3 Iron Oxides.- 3.1 Forms and Occurrence.- 3.2 Solution Chemistry of Iron in Soils.- 3.3 Surface Chemistry of Metal Oxides.- 4 Manganese Oxides.- 4.1 Mineralogy.- 4.2 Solubility.- 4.3 Sorption.- References.- 6 Assessing the Solubilities and Reaction Kinetics of Aluminous Minerals in Soils.- 1 Introduction.- 2 Experimental Determination of the Stabilities of Aluminous Minerals.- 2.1 The Al2O3-H2O System: Aluminium Hydroxides and Oxyhydroxides.- 2.2 The Al2O3-SO3-H2O System: Aluminum Sulfate Minerals in Acid Systems.- 2.3 The Al2O3-SiO2-H2O System: The Aluminosilicate Clay Minerals.- 3 Kinetics of Aluminous Mineral Precipitation/Dissolution Reactions.- 3.1 Kinetics of Hydroxy-Aluminium Solids Formation and Dissolution.- 3.2 Kinetics of Aluminosilicate Mineral Formation and Dissolution.- 4 Interaction of Aluminous Mineral Stabilities and Reaction Kinetics in Soils and Other Terrestrial Systems.- 4.1 Acidification Response in Natural Waters and Soils.- 4.2 Watershed-Scale Weathering Phenomena, Rates and Models.- References.- 7 Nutrient Status and Toxicity Problems in Acid Soils.- 1 Introduction.- 2 Soil Acidity and Nutrient Status.- 2.1 Nitrogen.- 2.2 Phosphorus.- 2.3 Potassium.- 2.4 Calcium.- 2.5 Magnesium.- 2.6 Sulphur.- 2.7 Copper.- 2.8 Zinc.- 2.9 Manganese.- 2.10 Iron.- 2.11 Boron.- 2.12 Molybdenum.- 2.13 Silicon.- 3 Toxicity Problems in Acid Soils.- 3.1 Manganese Toxicity.- 3.2 Al Toxicity in Relation to Ca Level and pH.- 3.3 Al Toxicity and Soil Organic Matter.- 3.4 Al Toxicity, Soil Solution Ionic Strength, and the Effect of Soil Drying Cycles.- 4 Ion Activities in the Soil Solution: An Alternative Perspective to Soil Acidity Problems.- 4.1 Relationship of Nutrient Uptake to Chemical Potentials.- 4.2 Chemical Potentials and Root Response to Ca and Al.- 5 Concluding Remarks.- References.- 8 Effects of Soil Acidity on Plant Associations.- 1 Introduction.- 2 Effects of Single Factors.- 2.1 Concentration of Ca-Ions.- 2.2 Concentration of H-Ions.- 2.3 Concentration of Al-Ions.- 2.4 NH4/NO3 Ratio.- 3 Interactions.- 3.1 Interaction of Ca with H and Al.- 3.2 Interaction of the N-Form with H and Al.- 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.