The Chemistry of Soils. Third Edition. By Garrison Sposito. Oxford University Press, 2016. Hardback, Pp. 272. Price GBP 59.00, EUR 216.00. ISBN 9780190630881

The completely revised third edition of this book by Garrison Sposito reflects the latest insights in the field and is a welcome update for those who want to have a fundamental insight into the processes in soils, insight which is needed to safeguard the crucial role of soils for life on earth. The first four chapters describe the components of soil, namely soil minerals, humus, gas and the soil solution. Chapter 1, The Composition of Soils, gives an introduction to the components of soil and reader’s attention is drawn to the natural capital of the soil. According to the author, ‘the critical assets derive primarily from three fundamental soil properties: texture, mineralogy and humus’. Chapter 2, Soil Minerals, describes nicely how soil minerals form, the structure of the minerals and how this determines their stability against weathering. Furthermore, the retention of ions by clay and metal oxide minerals is discussed. Chapter 3, Soil Humus, has been completely rewritten from previous editions and treats soil humus according to the new view on organic matter, of which the author has been one of the pioneers. Humification of plant and animal litter is described as an analogue to the weathering of minerals, and humus is seen as complex mixtures of identifiable molecules that can be attributed to their litter sources rather than considering the operationally defined fractions, including humin, humic and fulvic acids, to be unique new macromolecular compounds according to the classical view which is totally discarded here. Chapter 4, The Soil Solution, starts with a discussion of the methods used for sampling the soil solution. This is followed by descriptions of complex formation in the soil solution and the calculation method of chemical speciation. In this chapter, I, however, missed an explicit discussion of metal complexes with organic ligands which play a very important role in metal speciation. In the following chapters, the important chemical processes in soil, viz. mineral weathering, oxidation–reduction reactions, adsorption and ion-exchange, are discussed, together with a chapter on soil-particle surface charge and a chapter on soil colloids. These subjects are discussed thoroughly from a physical chemical perspective and give clear insights into the processes. Chapter 5, Mineral Weathering, first describes the mechanism of mineral weathering followed by mineral-weathering sequences. The chapter concludes with a section on phosphate transformations in calcareous soils and its implications on phosphate availability. Chapter 6, Oxidation–Reduction Reactions, describes the principles of redox reactions on the basis of the most relevant redox processes occurring in flooded soils and their sequence from oxidized to more and more reduced systems, which is known as the redox ladder. Finally, the construction of pE–pH diagrams is explained. In Chapter 7, Soil Particle Surface Charge, the concepts of structural charge due to the structural defects in minerals, and surface charge due to the adsorption of ions at the soil particle–water interface are discussed, together with various definitions for the ‘point of zero charge’, which is the pH at which the surface charge due to adsorption or desorption is zero. Chapter 8, Soil Adsorption Phenomena, deals mainly with the adsorption of both cationic and anionic species to soils. Adsorption of organic molecules is also discussed. ISSN 2053-2296