In keeping with the spirit of an Advanced Series in the Agricultural Sciences, we have attempted to address herein most of the current research areas being used to characterize, describe and manage salt-affected soils. Because of a certain amount of personal bias inherent in our individual viewpoints and backgrounds, some areas have been accorded more emphasis than others. It has been our goal, however, to provide either detail about, or at least a recent reference to, each major area of current soil salinity research. This information, coupled with what we hope to be a rather logical progression from descriptive material on equilibrium or near-equilibrium soil chemistry, through transport processes, to eventual management practices including some elementary economic decisions, should enable the reader to bridge the gap from introductory soil chemistry or soil physics texts to the basic literature of this area. The text will be perceived by the astute reader as somewhat uneven in its treatment of respective sections. We feel that this is to a certain extent appropriate, for it thus portrays the unevenness of progress to date in the corresponding areas of research. The management of saline and sodic soils remains largely an empirical semi-science or even art, whereas transport phenomena are normally dealt with in a much more theoretical (and also a much more highly mathematical) vein. Equilibrium soil chemistry has historically occupied an intermediate position with respect to its mix of empiricism and theoretical rigor.

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1 Diagnosis and Properties.- 1.1 Sources of Salts.- 1.1.1 Rainfall.- 1.1.2 Mineral Weathering.- 1.1.3 Fossil Salts.- 1.1.4 Man's Activities.- 1.2 Some Water Quality and Soil Solution Parameters.- 1.2.1 Common Water Quality Parameters.- 1.2.1.1 Total Salt Concentration.- 1.2.1.2 Electrical Conductivity (EC).- 1.2.1.3 Chemical Analyses.- 1.2.1.4 Sodium Adsorption Ratio (SAR).- 1.2.1.5 Langelier Index (pHc).- 1.2.1.6 Specific Ion Hazards.- 1.2.2 Physical Characterization of Soil Water.- 1.2.2.1 Soil Water Potential.- 1.2.2.2 Pressure and Head Equivalents of Soil Water Potential.- 1.2.2.3 Water (Solution) Retentivity Curve.- 1.2.2.4 Modeling of the Soil-Water-Salt Retentivity Function h(? C, R).- 1.2.3 Simplified Interactions of Irrigation Waters and Rainfall with Soils.- 1.2.3.1 Basic Concentration and Displacement Processes.- 1.2.3.2 Ion Exchange Phenomena.- 1.2.3.3 Dissolving and Precipitation of Minerals.- 1.3 Surface Phenomena of Salt-Affected Soils.- 1.3.1 Soil Minerals and Their Properties.- 1.3.1.1 Common Soil Minerals.- 1.3.1.2 Some Relevant Surface Properties of Soils.- 1.3.1.3 Water Retention and Swelling.- 1.3.1.4 Effects of Salts on Soil Hydraulic Parameters..- 1.3.1.5 Modeling of Hydraulic Conductivity K (?, R, C) Based upon Soil Water Retentivity.- 1.3.2 Ion Exchange and Exclusion.- 1.3.2.1 Mass Action Approaches.- 1.3.2.2 Diffuse Double Layer Approach.- 1.3.2.3 The Gapon Equation.- 1.3.2.4 Modeling of Na-Ca Exchange Equilibria.- 1.3.2.5 Anion Exclusion.- 1.3.2.6 Modeling of Anion Exclusion.- 1.3.2.7 Estimating the Osmotic Efficiency Coefficient Function ? (?,c).- 1.3.3 Retention of Uncharged Solutes.- 1.4 Salt Dissolution and Precipitation.- 1.4.1 Primary Minerals.- 1.4.2 Carbonate Minerals.- 1.4.3 Evaporite Minerals.- 1.5 Diagnosis of Salinity Problems.- 1.5.1 Diagnostic Parameters.- 1.5.2 Saline Conditions.- 1.5.3 Sodic Conditions.- 1.5.4 Other Salinity Problems.- 2 Transportation and Distribution of Salts.- 2.1 Water Movement Processes.- 2.1.1 Flow of Viscous Fluid.- 2.1.2 Darcy's Equation.- 2.1.3 Unsteady (Transient) Water Flow.- 2.1.4 Vapor Flow.- 2.1.5 Infiltration of Water into Soils.- 2.1.6 Redistribution of Soil Water.- 2.2 Salt Transport in Soils.- 2.2.1 Transport by Diffusion Without Solution Flow.- 2.2.2 Transport of Salt by Convection.- 2.2.3 Combined Effects of Diffusion and Convection on Salt Transport.- 2.2.4 Miscible Displacement in Soils.- 2.2.5 Solute Reflection During Water Flow.- 2.2.6 Solute Chromatography in Soils.- 2.2.6.1 Qualitative Description.- 2.2.6.2 Quantitative Description of Chromatographic Processes.- 2.2.6.3 Application of Chromatographic Theories to Soil Systems.- 2.2.7 Effects of Salinity on Soil Water Transmission Rates.- 2.2.7.1 Effects of Salt Concentration Gradients.- 2.2.7.2 Modified Solution Flux Equation.- 2.3 Modeling of Salt-Flow Phenomena.- 2.3.1 Mathematical and Numerical Models.- 2.3.2 Mathematical Modeling of Transport Phenomena in Soils.- 2.3.3 Numerical Methods Applied to Transient Flow Problems.- 2.3.3.1 Finite-Difference Methods.- 2.3.3.2 Finite Element Method.- 2.3.4 Salt Dynamics and Distribution in Fallow Soils.- 2.3.4.1 Noninteractive Solute.- 2.3.4.2 Solute Interacting with Soil.- 2.3.5 Modeling of Salt Dynamics and Distribution in Soils Under Crop Growing Conditions.- 2.3.5.1 Models for Water Extraction by Crop Roots.- 2.3.5.2 Computed Salt Distribution Profiles and Measured Data.- 2.3.6 Solute Dispersion and Distribution in Heterogeneous Field Soils.- 2.3.6.1 Piston Flow Profiles.- 2.3.6.2 Dispersive Profiles.- 3 Management.- 3.1 Crop Salt Tolerance.- 3.1.1 Osmotic Effects.- 3.1.2 Specific-Ion Effects.- 3.1.3 Plant Sensitivity.- 3.1.4 Crop Selection.- 3.2 Irrigation Practice.- 3.2.1 Irrigation Water Quality.- 3.2.2 Water Quality Classifications.- 3.2.3 Leaching Requirement.- 3.2.4 Drainage Water Quality.- 3.2.5 Salt Balance.- 3.3 Reclamation of Saline and Sodic Soils.- 3.3.1 Reclaiming Saline Soils by Leaching.- 3.3.2 The Use of Mulches and Other Surface Management to Enhance Salt Leaching.- 3.3.3 Gypsum Use for Reclaiming Sodic Soils.- 3.3.4 High Salt Water Leaching.- 3.3.5 Deep Mixing Sodic Soils for Reclamation.- 3.3.6 Sulfuric Acid for Reclaiming Sodic Soils.- 3.4 Solute Flow Models Applied to Irrigation Management Optimization.- 3.4.1 Reclamation of Saline Soils by Leaching.- 3.4.2 Quantity-Quality Substitutions of Water During the Irrigation Season.- 3.4.2.1 Modeling of Crop Response to Soil Salinity..- 3.4.2.2 Optimizing the Quantity-Quality Combination of the Irrigation Water.- 3.4.3 Models for the Economic Evaluation of Salinity in Irrigation Water Management.- 3.4.3.1 Least Cost Quantity-Quality Combinations Based on the Critical-Threshold Concept.- 3.4.3.2 Optimal Irrigation Management Based on the Total Potential Approach.- 3.4.3.3 Modeling of Optimal Irrigation Scheduling.- 3.5 Specialized Management Practices.- References.