Soil Humic Substances

Abstract Introduction Genesis The Lignin‐Protein Theory The Sugar‐Amine Theory The Polyphenol Theory Extraction, Fractionation and Purification Extraction Methods Fractionation Procedures Purification Procedures Sequential Extraction/Fractionation Procedures Comprehensive Isolation Procedure Proposed by the IHSS Chemical Composition, Properties and Structure Elemental Composition Functional Groups Charge Characteristics and Cation Exchange Capacity Molecular Weight, Size and Shape Structural Components Molecular Models Fractal Nature Soil Fertility Functions Physical Functions Chemical Functions Nutritional Aspects Biological Actions Environmental Functions Interactions with Organic Pollutants Interactions with Trace Metals Summary and Concluding Remarks